Introduction
Idiopathic pulmonary fibrosis (IPF) is a chronic progressive lung disease characterized by progressive lung fibrogenesis and the histological features of usual interstitial pneumonia (UIP). Symptoms include increased cough and dyspnea, which reduces the quality of life. The median survival of patients with IPF is 3–5 years from diagnosis.[1] The diagnosis of IPF requires the exclusion of interstitial lung disease (ILD) with known causes and the identification of a pattern of UIP assessed either using high-resolution computed tomography (HRCT) or based on histology. However, HRCT is not always useful for diagnosis because other chronic fibrotic lung disorders, such as chronic hypersensitivity pneumonitis (cHP) and ILD associated with connective tissue diseases (CTD-ILD), can exhibit a UIP-like pattern.[2,3] Additionally, many patients are unable to tolerate lung biopsy.[4] Therefore, biomarkers that are easy to implement, yet sensitive and specific, are needed for the diagnosis of IPF.
We searched the PubMed database for articles published from 2005 to 2020 using the keywords “marker” or “biomarkers” or “signature” and “idiopathic pulmonary fibrosis.” In the present study, we summarize over 100 biomarkers identified in the serum, bronchoalveolar lavage fluid (BALF), lung tissue, and sputum. The biomarkers related to IPF reported in the literature can be divided into the following six categories according to their functions.
Differentially Expressed Biomarkers in the IPF Group Compared With Healthy Controls (HCs)
Our previous study schematically summarized the pathogenesis of IPF.[1] According to the different roles played in the pathogenesis of IPF, the differentially expressed biomarkers in IPF can be further divided into nine different categories, as summarized in Figure 1 and Supplementary Table 1, https://links.lww.com/CM9/B165.
;)
Figure 1: Relationships between markers for diagnosis of IPF and the pathogenesis of IPF. AECs: Alveolar epithelial cells; bFGF: Basic fibroblast growth factor; CD: Cluster of differentiation; ECM: Extracellular matrix; EMT: Epithelial-mesenchymal transition; ER: Endoplasmic reticulum; HDACs: Histone deacetylases; Hsp: Heat shock protein; IGF: Insulin-like growth factor; IPF: Idiopathic pulmonary fibrosis; M-CSF: Macrophage colony stimulating factor; PDGF: Platelet-derived growth factor; PLGF: Placental growth factor; PRDX: Peroxiredoxin; TGF-β: Transforming growth factor-β; Th: T helper; VEGF: Vascular endothelial growth factor.
Alveolar epithelial cells (AECs) dysfunction markers
Krebs von den Lungen (KL)-6: Baseline serum[5–8] and sputum[9] levels of KL-6 are significantly higher in patients with IPF than in HCs. The optimal cutoff values (Youden index) of serum KL-6 for discriminating IPF patients from HCs have been reported as 476 U/mL[9] or 398 U/mL.[5] KL-6 exerts chemotactic and antiapoptotic effects on fibroblasts in vitro,[10,11] suggesting a role in the pathogenesis of IPF.
Surfactant protein (SP)-A and SP-D: Baseline serum levels of SP-A and SP-D in patients with IPF are significantly higher than those in HCs,[6,8,12] a finding that was supported by the results of a meta-analysis including 21 studies and 1289 IPF patients.[13] IPF patients exhibit a two-fold higher BALF level of SP-A than HCs,[14] and lung tissue samples of patients with IPF show higher SP-A immunoreactivity in hyperplastic AECs.[14] In contrast, levels of SP-D expression were downregulated in explanted lung samples of patients with IPF compared to HCs.[15] The cutoff values of SP-A and SP-D for the detection of IPF were reported as 45 ng/mL and 110 ng/mL, respectively.[12] Another study reported similar cutoff values (44 ng/mL for SP-A and 107 ng/mL for SP-D) for distinguishing IPF patients from HCs.[6] Altered levels of SP-A and SP-D can arise from abnormal function or proliferation of type II AECs caused by injury.[16]
Receptor for advanced glycation end-products (RAGE): Patients with IPF were shown to have significantly higher RAGE levels in the serum[17] and lung tissue[18] than in HCs. Serum RAGE level correlated with levels in BALF specimens[17] and was shown to be a marker of type I AECs injury and/or proliferation.[19]
Haptoglobin: The serum level of haptoglobin was lower in patients with IPF than in HCs.[19,20] Haptoglobin functions as a scavenger of hemoglobin circulating in serum, and is released by hemolysis or through normal red blood cell turnover, thereby protecting against the toxic effects of free heme and exerting antioxidant and immunomodulatory effects.[21]
Transferrin: Transferrin receptor 1, also known as cluster of differentiation (CD) 71, is an integral membrane protein that mediates the uptake of diferric transferrin complexes through receptor-mediated endocytosis.[22] The proportion of airway macrophages (AMs) lacking CD71 was shown to increase in patients with IPF compared to HC, and CD71−/− AMs showed an impaired ability to sequester transferrin, resulting in increased BALF concentrations of transferrin in patients with IPF.[23]
Mucin (MUC) 5B: To date, 21 human MUC genes encoding mucins have been identified, of which 16 are expressed in the lung.[24] MUC5AC and MUC5B together account for approximately 90% of the mucin content of sputum.[25]MUC5B is upregulated in the lungs of patients with IPF compared to HCs,[15] and immunohistochemical analysis revealed that the proportion of MUC5B-positive cells in the distal airways but not in the honeycomb cysts is more than two-fold higher than HCs, whereas the proportions of MUC5AC-positive epithelial cells of distal airways were similar between the two groups.[26] The overexpression of MUC5B in distal airways but not honeycomb cysts in the lungs of IPF patients may be driven by a single nucleotide polymorphism in the MUC5B gene.[27]
Serum amyloid A (SAA): SAA levels are much higher in patients with IPF than in HCs; the cutoff value of SSA for differentiating the two groups has been reported to be 6067 ng/mL.[28] SAA is produced by lung fibroblasts[29,30] and can induce the overproduction of matrix metalloproteinases (MMPs) including MMP1, MMP5, and MMP7.[31]
Caspase-cleaved cytokeratin-18 (cCK-18): The level of cCK-18, a marker of AEC apoptosis, was found to be significantly elevated in the serum of IPF patients compared to HCs. cCK-18 was also shown to be present in the alveolar epithelium of lungs of IPF patients.[32]
Serum Mac-2-binding protein (M2BP): M2BP levels were shown to be significantly higher in patients with IPF than in HCs.[33] M2BP, which is expressed in alveolar macrophages and AECs,[33] is a ligand of galectin (Gal)-3, also known as Mac-2, which mediates cell adhesion and promotes fibrosis through the receptor-ligand interaction, and may play a role in the host's response against infection and cancer.[34–36]
Club cell protein 16 (CC16): CC16 is a putative anti-inflammatory protein produced by club cells as well as bronchiolar epithelial cells and AECs.[37] CC16 levels in the serum and BALF are increased in IPF patients; the optimal cutoff value of serum CC16 for differential diagnosis of IPF patients from HCs was determined to be 41 ng/mL.[37]
Oncomarkers: Fibroblasts in fibroblastic foci and cultured fibroblasts derived from the lungs of patients with IPF express high levels of carbohydrate antigen (CA) 153.[38] Proliferating AEC II from IPF lungs strongly expressed CK19.[38] Serum carcinoembryonic antigen (CEA) concentration was shown to be elevated in almost half of IPF patients,[39] while CEA levels in BALF increase in 45% of IPF patients who are non-smokers.[40,41] Immunohistochemical analysis revealed that CEA localizes to the metaplastic epithelium lining of honeycombed bronchioles[39]; CEA upregulation in honeycomb cysts and its subsequent release in blood may be responsible for the increased levels of CEA observed in the BALF of IPF patients.
Taken together, among the AEC markers, KL-6, SP-A, SP-D, RAGE, haptoglobin, and MUC5B were more well studied than other markers. KL-6 has antiapoptotic effects on fibroblast, SP-A and SP-D represent abnormal proliferation or injury of AECs II, RAGE represents abnormal proliferation or injury of AECs I, and haptoglobin is a protective factor with antioxidant and immunomodulatory effects. These five markers should be promoted in clinical practice, and their clinical value should be further evaluated. For other alveolar epithelial markers, more clinical studies are needed.
Fibrogenesis and extracellular matrix (ECM) remodeling markers
MMPs: MMP1 levels in the plasma, BALF[4,42] and lung tissue[15,42,43] of patients with IPF were significantly higher than those in HCs. MMP1 is an enzyme that cleaves fibrillar collagen, an ECM component that is enriched in IPF lungs. It is primarily localized in the reactive alveolar epithelium but is mostly absent in fibroblasts of the interstitial compartment.[44] MMP3 was upregulated in the serum[45] and lung[45–48] of IPF patients relative to HCs, and is thought to contribute to the pathogenesis of IPF by inducing epithelial-to-mesenchymal transition (EMT).[44] MMP7 levels were significantly higher in plasma or serum,[4,6,8,42,49,50] BALF,[4,42,51] and lung tissue[42] of patients with IPF as compared to HCs; and a serum cutoff value of 6 ng/mL could distinguish between these two groups.[6,52] Also, MMP7 may mediate the profibrotic effects of osteopontin (OPN)[53] and facilitate the release of transforming growth factor (TGF)-β from the extracellular proteoglycan decorin, thereby promoting TGF-β activation.[54] MMP8 levels in plasma, BALF, and lung tissue homogenates were reported to be significantly higher in IPF patients compared to HCs.[42,55–57] In an experimental model, MMP8 enhanced inflammation and consequent fibrosis, and MMP8−/− mice were protected against bleomycin-induced lung fibrosis through mechanisms that have yet to be elucidated.[58] MMP9 levels are higher in the serum,[59] lungs,[60] and sputum[9] of IPF patients compared to HCs. MMP9 is expressed by AECs, macrophages, neutrophils, and fibroblasts in fibroblastic foci.[60] Baseline serum levels of MMP10,[50] MMP28,[61] and tissue inhibitor of metalloproteinase (TIMP) 3[59] were also elevated in IPF patients, and MMP28-deficient mice were protected from bleomycin-induced lung fibrosis, suggesting a profibrotic role for MMP28.[62] Moreover, MMP28 may contribute to EMT, which has been implicated in the pathogenesis of IPF, by inducing TGF-β activation.[62]
Periostin (POSTN): Serum POSTN levels have been reported to be upregulated in IPF patients compared to HCs[15] and can be used to distinguish between these two populations.[5,63] A semiquantitative analysis of POSTN expression in lung tissue showed that it was upregulated in IPF.[64] The cutoff value of POSTN for distinguishing IPF patients from HCs was determined to be 77 ng/mL, which had a sensitivity of 73.3% and specificity of 79.6%.[5] POSTN plays an important role in the pathogenesis of pulmonary fibrosis by stimulating the production of inflammatory cytokines such as tumor necrosis factor (TNF)-α or interleukin (IL)-1α and activating nuclear factor (NF)-κB, leading to the production of various inflammatory cytokines and chemokines and lung fibrosis.[64,65] POSTN also promotes connective tissue growth factor (CTGF) production by fibrocytes, myofibroblast differentiation of fibroblasts, and collagen deposition, resulting in pulmonary fibrosis.[66,67] Finally, POSTN may contribute to fibrosis by promoting EMT of lung fibroblasts in IPF[68] via activation of the TGF-β signaling pathway.
OPN and alpha-actin-2 (ACTA-2): OPN mRNA and protein levels were shown to be significantly higher in the serum, BALF, and lung tissue of patients with IPF compared to HCs.[15,51,52,69] OPN is a matricellular protein produced by macrophages that induces migration, proliferation, and adhesion of fibroblasts and is implicated in the pathogenesis of IPF.[70,71] ACTA-2 mRNA[15,72] and protein[73] levels were higher in the lungs of IPF patients compared to HCs, which may be related to myofibroblast differentiation and proliferation and matrix remodeling.
Follistatin (FST), fibulin-1 (FBLN-1), and syndecan 2 (SDC2): The mRNA expression of the activin inhibitor FST was upregulated in IPF lungs,[74] and serum concentrations of FST were significantly higher in patients with IPF compared to HC subjects.[75] FBLN-1 is produced by lung fibroblasts and is required for the formation of alveolar septum.[9] FBLN-1 levels in the serum and lung tissue were increased in patients with IPF compared to HC.[76] The increased production of FBLN-1 likely reflects in the activated fibrogenic state of fibroblasts derived from patients with IPF.[77] SDC2 levels were increased in the lung tissue of patients with IPF, and may contribute to fibrosis by enhancing the assembly and deposition of ECM.[78]
Among the fibrogenesis and ECM remodeling markers, MMPs, POSTN, OPN, and ACTA-2 were more well studied than other markers. They induce EMT, migration, proliferation, and adhesion of fibroblasts, myofibroblast differentiation of fibroblasts, and collagen deposition, resulting in pulmonary fibrosis.
Immune dysfunction/regulation markers
YKL-40: The levels of YKL-40 in the serum and BALF were significantly higher in patients with IPF than in HCs,[8,79–81] which may be related to lung tissue remodeling that occurs in patients with IPF.[82]
Programed cell death-1 (PD-1): PD-1 upregulation was shown to be profibrotic through its capacity to enhance the expression of signal transducer and activator of transcription (STAT) 3, leading to the production of profibrotic cytokines such as TGF-β and IL-17A.[83] Cell surface expression of PD-1 detected by immunohistochemistry in CD4+ T cells was significantly higher in IPF patients than in HCs.[83]
S100A6, S100A9, and S100A12: The S100 family of calcium-binding proteins has over 20 members. S100A6[84] and S100A9[51,85,86] levels were higher in the BALF of patients with IPF than in HCs; and S100A12 transcript expression was higher in the lungs of patients with IPF than in HCs.[87] S100A9 induces neutrophil recruitment.[88,89] Serum and BALF levels of S100A9 significantly correlated with BALF neutrophil counts.[85,86] Sustained neutrophil accumulation in the alveolar space and neutrophil-mediated injury to the alveolar wall contribute to interstitial fibrosis.[90] S100A9 also stimulates the proliferation of fibroblasts, which plays an important role in the development of lung fibrosis.[91]
Toll-like receptor 9 (TLR9): The innate immune sensor TLR9 has been reported to be upregulated in the lung tissue of IPF patients.[92] The overexpression of TLR9 in pulmonary fibroblasts in lung biopsies of IPF patients was able to induce myofibroblast differentiation,[92] and TLR9 expressed in an AEC line promoted EMT,[93] contributing to the pathogenesis of IPF.
Gal-1 and Gal-3: BALF levels of Gal-1[94] and Gal-3[95] were higher in patients with IPF than in HCs. Gal-1 skews the helper T cell (Th)1/Th2 balance toward the Th2 phenotype in fibrotic diseases. It also induces macrophage polarization to the M2 phenotype,[96] resulting in the accumulation of profibrotic mediators that promote accumulation and differentiation of fibroblasts into myofibroblasts as well as collagen production and deposition.[1] Alveolar macrophages in IPF patients had higher Gal-3 expression than macrophages of HCs,[95] suggesting that the higher Gal-3 concentration in BALF in IPF was at least partially due to increased production by alveolar macrophages. Gal-3 contributes to the pathogenesis of IPF by activating macrophages and fibroblasts and promoting inflammation through increased TNF-α production by macrophages, leading to a positive feedback loop between TNF-α and Gal-3. Additionally, Gal-3 stimulated fibroblast migration and collagen synthesis in vitro, suggesting that it directly affects fibrogenesis.[95]
Defensin, heme oxygenase-1 (HO-1), cystatin C, TNF receptor superfamily member (TNFRSF) 1A and 1B: Serum levels of α-defensin (HAD),[97,98] β-defensin (HBD) 1, and HBD2[98] in patients with IPF were significantly higher than in HCs, although there were no differences in HBD levels in the BALF.[98] HBD2 was shown to be expressed in AEC II,[99] implying that it is important for lung function. HO-1 was shown to be expressed at a lower level in the lung tissue of IPF patients compared to HCs.[15] Cystatin C is highly expressed in myofibroblasts of IPF patients,[100] and may promote the development of lung fibrosis by impairing the collagenolytic activity of cysteine cathepsins. The protein level of cystatin C, the most potent circulating inhibitor of cathepsins, was higher in BALF samples from IPF patients than in those of HCs.[100] Serum protein levels of the soluble TNFRSF1A and TNFRSF1B were shown to be significantly higher in IPF patients than in HCs.[42]
αvβ6 integrin: αvβ6 integrin immunopositivity was higher in the lung tissues of patients with IPF than in those of HCs.[101] αvβ6 integrin is expressed in the alveolar epithelium[101] and activates TGF-β1, a key pro-fibrotic mediator.[102] αvβ6 integrin also regulates other basic cellular functions such as proliferation,[103] migration,[104] and ECM degradation.[105]
Anti-heat shock protein (Hsp) 70: Anti-Hsp70 immunoglobulin G (IgG) autoantibodies were more frequently detected in IPF patients than in HCs.[106] IgG autoantibodies can cause cytotoxicity and promote neutrophil recruitment via formation of antibody–antigen complexes and complement activation in target organs.[107] Neutrophilia is a prominent feature of IPF.[4,108]
Among these markers, YKL-40, PD-1, TLR9, S100A9, Gal-1, Gal-3, αvβ6 integrin, and anti-Hsp70 were more well studied. They may lead to lung tissue remodeling, collagen synthesis, and the production of profibrotic cytokines, and induce myofibroblast differentiation, proliferation of fibroblasts, EMT, and inflammation, contributing to pulmonary fibrosis. Although studies have reported that the expressions of defensin, HO-1, cystatin C, TNFRSF1A, and TNFRSF1B are up-regulated in IPF patients, their pathogenic mechanism is not completely clear, and there is still a long way to go before their clinical application.
Inflammation markers
Chemokines: The levels of C-X-C motif chemokine ligand (CXCL) 7 in the BALF[51]; CXCL8 (or IL-8) mRNA and protein levels in sputum[9]; and serum levels of CXCL8,[75] CXCL10,[109] CXCL13,[110] and CXCL14[111] were shown to be elevated in IPF patients compared to HCs. The CXCL10 is a cytokine that is induced in monocytes and macrophages by interferon (IFN)-γ and mediates the recruitment of activated lymphocytes to the lungs.[112] Cells of the macrophage lineage express high levels of CXCL13 in patients with IPF.[110] CXCL13 binds to the C-X-C motif chemokine receptor (CXCR) 5 expressed on the B cell surface to mediate B cell trafficking. CXCL14 expression was induced by Sonic hedgehog (Hh) overexpression in the mouse lung.[111] Hh signaling contributes to fibrogenesis and cross-talk with other signaling pathway components in IPF such as TGF-β, fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), and IL-13 to promote myofibroblast differentiation, ECM production, and cell motility and survival.[113,114] Thus, CXCL14 is a peripheral biomarker of Hh signaling activation.
BALF levels of C–C motif chemokine ligand (CCL) 2,[115,116] CCL3,[115] CCL4,[115] CCL16,[37] CCL18,[51] and CCL24[51] and serum levels of CCL2,[116] CCL16,[37] and CCL18[8,59] were significantly higher in IPF patients than in HCs. CCL2 and CCL3 are produced by a variety of cells including alveolar macrophages, monocytes, epidermal cells, lymphocytes, fibroblasts, and endothelial cells.[116] CCL2 and CCL3 are both proinflammatory chemokines responsible for homing and migration of lymphocytes and for the recruitment of mononuclear macrophages.[116] Alveolar macrophages play an important role in the pathogenesis of lung fibrosis.[117,118] After binding to the CCR2 receptor, CCL2 induces the expression of MMP2, MMP9, and TGF-β1 or stimulates the proliferation of fibroblasts by interacting with IL-13, leading to fibrosis.[119] CCL16 is expressed by bronchioles and AECs,[37] while CCL18 is mainly produced by macrophages.[120] CCL18 upregulates collagen production by lung fibroblasts.[120]
Interleukins: Levels of IL-4 level in the BALF[121] and of IL-6 mRNA in the sputum[9] were significantly higher, whereas serum concentrations of IL-10 and IL-15 were lower[69] in patients with IPF than in HCs, although another study found that IL-10 levels in BALF increased in IPF.[121] IL-6 contributes to both inflammation and fibrosis.[122]
Adhesion molecules
Intercellular adhesion molecules (ICAMs) 1, 2, 5, and E-selectin: Serum levels of ICAM1,[8] ICAM2,[123] and ICAM5[59,124] and ICAM1 levels induced in the sputum[123] were higher in patients with IPF than in HCs. They participate in lymphocyte recruitment to the interstitium and the areas of honeycombing.[125] Soluble E-selectin was present at a higher level in the serum of IPF patients compared to HC subjects.[126]
Insulin-like growth factor-binding protein (IGFBP): Serum levels of IGFBP-1[7,42] as well as serum[7] and sputum[9] levels of IGFBP-2 were significantly higher in IPF patients than in HC subjects. IGFBP-2 was also observed in the BALF of patients with ILD.[127] IGFBP-3, IGFBP-5, and IGFBP-6 levels were increased in lung tissue of IPF patients and in cultured fibroblasts isolated from IPF patient lungs.[15,128] IGFBPs are thought to induce the initiation and/or progression of fibrosis by stimulating the production of components of the ECM such as collagen type I and fibronectin in lung fibroblasts.[128] IGFBP-5 is also involved in EMT; collagen deposition; and peripheral blood mononuclear cell proliferation, infiltration, and senescence.[15]
Platelet endothelial cellular adhesion molecule (PECAM), latent TGF-β2-binding protein (LTBP), and histidine-rich glycoprotein (HRG): Serum PECAM-1 levels were significantly higher in IPF patients than in HCs.[129] PECAM-1 plays a role in leukocyte transmigration. LTBP2 is secreted by myofibroblasts[130] and the serum levels of LTBP2 were found to be higher in patients with IPF than in HCs; the optimal cutoff level to discriminate between these two populations was 15.1 ng/mL. HRG concentration was significantly diminished in plasma but increased in the BALF of IPF patients compared to HC subjects.[131] HRG was shown to suppress EMT in vivo[132]; this effect may be compromised in IPF patients due to their low levels of plasma HRG.
Growth factors
Insulin-like growth factor (IGF): Serum levels of IGF-1 and IGF-2 were decreased in patients with IPF compared to HCs[7]; and in an animal model, IGF-1[133] and IGF-2[134] induced myofibroblast differentiation, which is a critical step in the development of pulmonary fibrosis. IGF-2 also exerts profibrotic effects by inhibiting protease production and degradation of ECM, and stimulating the expression of two TGF-β isoforms.[134]
Platelet-derived growth factor subunit A (PDGFA): Gene expression profiling showed that PDGFA was downregulated in the serum of IPF patients compared to that of HCs.[69]
Vascular endothelial growth factor (VEGF): VEGF mRNA and protein levels were lower in BALF of patients with IPF than in HCs.[15,135,136] This decrease can be attributed to the apoptosis of vascular endothelial cells or to damage to the AECs, which are the main sources of VEGF in the lung.[135,136]
Macrophage colony stimulating factor (M-CSF): M-CSF was shown to induce CCL2 production and secretion in vitro and in vivo, and in fibroblasts, CCL2 induced collagen production, as well as TGF-β,[137] which stimulated CTGF expression.[138] M-CSF-induced CCL2 secretion may promote mononuclear phagocyte recruitment, fibroblast proliferation, TGF-β-mediated CTGF expression, and fibrosis. Patients with IPF had higher levels of M-CSF in BALF but not in serum compared to HCs.[116]
Basic fibroblast growth factor (bFGF) and placental growth factor (PLGF): bFGF is a potent mitogenic factor for fibroblasts and myofibroblasts, and bFGF levels were shown to be correlated with ECM production.[139] bFGF was observed to be upregulated in the mast cells of the lung tissue from patients with IPF[139]; and the levels of bFGF and PLGF in BALF were significantly higher in patients with IPF than in HCs.[121]
TGF-β, activin-A and activin-B: TGF-β mRNA and protein levels in sputum were found to be higher in patients with IPF than in HCs.[9] Activins belong to the TGF-β superfamily of growth factors and mainly signal through serine/threonine kinase receptors that induce Smad signaling.[140] Activins are involved in lung fibroblast proliferation and differentiation.[141] The genes encoding activin-A and activin-B were upregulated in lung tissue of IPF patients compared to HCs[74]; and the immunoreactivity of activin subunits was increased in hyperplastic AECs of IPF lungs.[74]
Hsp
Hsp27,[73] Hsp70,[135] Hsp90-α, and Hsp90-β[73] were upregulated in the lung tissue of IPF patients compared to HC subjects, and Hsp72 was found to be elevated in the serum of IPF compared to HC.[142] Lung biopsies of IPF patients showed high expression of Hsp72 in hyperplastic AEC II near fibrotic foci.[142] It was reported that Hsp27 expression is upregulated in lung fibroblasts in pulmonary fibrosis and that Hsp27 contributes to the fibrotic process by modulating lung fibroblast differentiation via Smad3 and extracellular signal-regulated kinase (ERK) pathways.[143] Hsp70, which is primarily distributed in different pulmonary cells including airway and AECs, macrophages, and endothelial cells, is an autoantigen for CD4+ T cells in IPF that can induce lymphocyte proliferation and IL-4 production.[135] Hsp90 is a positive regulator of fibroblast activation; inhibition of Hsp90 ATPase activity was shown to attenuate pulmonary fibrosis.[144] Taken together, Hsp may contribute to the fibrotic process by modulating lung fibroblast differentiation or activation, and by inducing lymphocyte proliferation or inflammation. The specimen types in these related studies are mainly lung tissue. In clinical practice, we can further observe the clinical value of HSP by performing immunohistochemistry on the lung tissue of IPF patients.
CD markers
CD11b (integrin subunit alpha M, ITGAM), CD16a (Fc gamma receptor [FCGR] 3A, FCGR3A), CD18 (integrin subunit beta 2, ITGB2), CD32a (FCGR2A), CD66d (CEA cell adhesion molecule 3, CEACAM3), and CD87 (urokinase-type plasminogen activator receptor [UPAR]) were up-regulated, while CD25/interleukin 2 receptor, alpha chain (IL-2RA) and D301/Clen10a were down-regulated in serum from IPF patients.[69] These results are mainly from gene expression analysis by real-time quantitative polymerase chain reaction (RT-qPCR) of whole blood from control and IPF subjects; future studies can further explore the clinical value of these CD molecules with BALF and lung tissue samples and further validate the assay at the protein level. CD133 (or prominin-1) was highly expressed in the lung of IPF patients compared to HCs and may be involved in EMT.[15] CD163 is a transmembrane protein expressed on the cell membrane of monocytes and macrophages,[145] while soluble CD163 (sCDl63) is present in serum and tissue fluid.[146] CD163 is a marker of activated M2 macrophages. IPF patients were shown to have high expression of sCD163, suggesting that it promotes pulmonary fibrosis by inducing M2 macrophage polarization.[109] The protein levels of CD248, also known as endosialin, were reported to be higher in lung fibroblasts derived from IPF patients than in those from normal lungs, and silencing of CD248 expression significantly reduced the proliferation of lung fibroblasts.[106]
Enzymes
Serum levels of lactate dehydrogenase (LDH),[5] napsin A,[147] peroxiredoxin (PRDX)4,[148] and a disintegrin and metalloproteinase (ADAM)17 and levels of ADAM17 in peripheral blood mononuclear cells[149] were higher in IPF patients than in HCs. PRDXs are a recently identified family of antioxidants consisting of six members in mammals (PRDX1–PRDX6). However, overexpression of PRDX4 in the lung may not exert a protective effect but may, instead, exacerbate pulmonary fibrosis by inducing inflammatory cytokine production.[148] In a murine model, PRDX4 was expressed in alveolar macrophages and AECs.[148] Class I and II histone deacetylases (HDACs) were shown to be overexpressed and upregulated in lung tissue from patients with IPF compared to control subjects.[150] Aberrant overexpression of HDACs in the lung of patients with IPF can contribute to alveolar bronchiolization and the generation of fibroblasts resistant to apoptosis.[150] BALF levels of pepsin, a marker of gastric aspiration, was significantly elevated in patients with IPF compared to HCs.[151]
Other markers
The p16 protein encoded by the CDKN2A gene was shown to be upregulated in the lung of patients with IPF. Immunohistochemical analysis showed that the expression of p16–a marker of senescence–in lung fibroblasts is a potential diagnostic biomarker in IPF.[15] High mobility group box (HMGB) binds to membrane-bound receptors, such as RAGE and TLR. Their interactions lead to the activation of pro-inflammatory intracellular signaling, which is associated with the pathophysiology of IPF.[152] Nitric oxide (NO) is an intracellular signaling molecule involved in inflammation and nitrosative and oxidative stress, which play an important role in lung fibrogenesis.[153,154] Serum levels of HMGB1[154] and alveolar concentration of NO (CaNO)[155] were found to be higher in IPF patients than in subjects with HC.
As described in our previous review,[1] IPF is likely the result of complex interactions between environmental, genetic, and epigenetic factors. The pathogenesis of IPF involves various imbalances centered on AEC/fibroblast apoptosis imbalance, including endoplasmic reticulum (ER), telomere length homeostasis, mitochondrial dysfunction, oxidant/antioxidant imbalance, Th1/Th2 imbalance, M1–M2 polarization of macrophages, protease/antiprotease imbalance, and plasminogen activation/inhibition imbalance. Among them, AEC/fibroblast apoptosis imbalance is the core of the pathogenesis of IPF, because although other imbalances affect each other and promote each other, they eventually lead to dysregulated crosstalk between AECs and fibroblasts. As a result, the dysregulated crosstalk and abnormal mediators between them result in AECs apoptosis, fibroblast anti-apoptosis, and abnormal ECM.
AEC dysfunction markers and growth factors (VEGF) are produced by aberrantly activated AECs or are related to the damage, apoptosis, and senescence of AECs. Growth factors (IGF-1, 2′ M-CSF, PDGFA, bFGF, and PLGF), fibrogenesis and ECM remodeling markers, Hsp (Hsp27 and Hsp90), and enzymes (HDACs) are related to fibroblast anti-apoptosis, proliferation, and differentiation. Therefore, these types of biomarkers represent AEC/fibroblast apoptosis imbalance. Under normal conditions, there is a dynamic balance between AECs and fibroblasts. In the normal repair of AECs, activated fibroblasts produce ECM and provide a provisional scaffold for AECs migration, proliferation, and re-epithelization. After the AECs damage has been repaired, fibroblasts undergo apoptosis in order to restore normal cellular homeostasis and maintain tissue architecture and organ function. Fibroblast apoptosis is essential in normal wound healing but is dysregulated in IPF. In IPF patients, AECs undergo damage, aging, and apoptosis, while fibroblasts undergo proliferation, differentiation, and anti-apoptosis, which contributes to AEC/fibroblast apoptosis imbalance, leading to abnormal ECM and pulmonary fibrosis.
Immune dysfunction/regulation markers, inflammation markers, adhesion molecules, Hsp (Hsp70), CD markers, and enzymes (HDACs) are mainly related to inflammation and immune response (Th1/Th2 imbalance, M1–M2 polarization of macrophages). Th1 and Th2 cells take on opposite roles in fibrogenesis. Th1 cells and their secretory cytokines (IFNγ) are thought of as being antifibrotic. By contrast, Th2 and associated cytokines (IL-4, IL-5, and IL-13) exhibit a profibrotic property. An overzealous or prolonged M2 polarization results in excessive amounts of profibrotic mediators, which promote fibroblast accumulation and the differentiation of fibroblasts into myofibroblasts, and collagen production and deposition. Therefore, Th1/Th2 imbalance and M1–M2 polarization of macrophages are actually an imbalance between profibrosis and antifibrosis.
Fibrogenesis and ECM remodeling markers are also related to protease/antiprotease imbalance, which may cause fibrosis by promoting EMT, inflammation, promoting M1–M2 polarization, and activating TGF-β signaling.
Biomarkers That Are Specific for IPF
The gene expression of MMP-1, MMP-2, MMP-7, POSTN, OPN, ACTA-2, IGFBP-5, and Prominin-1 were increased in patients with IPF compared to NSIP.[15,63,156] Serum levels of SP-D >31 ng/mL, MMP-7 >1.75 ng/mL, and OPN >6 ng/mL each significantly distinguished patients with IPF compared with patients with alternative idiopathic ILDs (a-ILD).[156] A study identified a gene signature that was truly specific for IPF compared to nonspecific interstitial pneumonia (NSIP), which includes MUC5B, ACTA-2, and IGFBP-5.[15] MMP28 in serum is able to distinguish IPF from cHP and CTD-ILD.[61] BALF levels of HAD[98] and serum levels of PDGF-BB, granulocyte-colony stimulating factor (G-CSF), FST, and PECAM-1[75] in patients with IPF were significantly higher than in patients with sarcoidosis. BALF S100A9 levels were significantly higher in IPF patients than in patients with sarcoidosis or those with systemic sclerosis.[157] Serum levels of cCK-18 were significantly different in IPF patients compared with patients with HP or with NSIP patients.[32] Serum CC16 was found significantly higher in IPF compared with cHP and CTD-ILD.[37] CaNO has also been reported to have the best diagnostic accuracy to discriminate CTD-ILD from idiopathic ILDs.[158] CTD-ILD patients reported significantly higher values of CaNO than in patients with IPF.[158]
Biomarkers for Differentiating AE-IPF From Stable IPF
The diagnostic criteria for IPF AE include a clinical worsening within 30 days, and the presence of new radiologic abnormalities on HRCT characterized by a new bilateral opacification/consolidation of ground glass not fully explained by cardiac failure or fluid overload.[159] Among the differentially expressed biomarkers in the IPF group compared with HCs, the following markers may be helpful for differentiating AE-IPF from stable IPF: KL-6,[160,161] SP-A,[162] SP-D,[160,161] haptoglobin,[163] S100A9,[163] α-defensin,[164] CXCL8,[165,166] CXCL13,[10] CCL2,[166] CCL18,[166] CCL22,[166] IL-6,[165] LTBP2,[130] and HMGB1.[167]
Biomarkers Predicting Disease Progression
Disease progression of IPF is defined as a decrease in lung function (defined as either a ≥10% decline in the forced vital capacity [FVC]% predicted value [%FVC], or a ≥15% decline in the diffusion capacity of the CO [DLCO]% predicted value [%DLCO]), an increase of the honeycombing score on HRCT, respiratory hospitalizations, AE of IPF, lung transplantation, or mortality from any cause.[8,50,158] Among the biomarkers that are differentially expressed in the IPF group, the following can predict disease progression: KL-6,[6] SP-A,[12,13] SP-D,[12,168] RAGE,[17] M2BP,[33] CEA,[168] MMP3,[45] MMP7,[9,26,42,54] MMP10,[50] MMP28,[61] POSTN,[5,15,63] YKL-40,[81] S100A12,[87] anti-HSP70,[106] TLR9,[93] αvβ6 integrin,[101] CXCL8,[165] CXCL10,[109] CXCL13, CXCL14,[169] CCL2, CCL18,[169] IL-6,[165] ICAM 1,[87] E-selectin,[126] CD71,[23] VEGF,[170] LDH,[171] HMGB1,[172] and alveolar NO.[173]
Biomarkers Related to Disease Severity
The disease severity of IPF is often assessed by lung function parameters, such as FVC or %FVC, FEV1%predicted value (%FEV1), DLCO or %DLCO, and total lung capacity (TLC),[59,174] fibrosis score on HRCT,[93,175] the 6-min walking distance (6MWD),[59] and the composite physiological index (CPI).[59] Among the biomarkers differentially expressed in the IPF group, the following biomarkers are related to the severity of the disease: KL-6, RAGE,[17] M2BP,[33] SAA,[28] CEA,[39] MMP3,[45] MMP7,[9,42,50,54] MMP10,[50] MMP28,[61] YKL-40,[79] α-defensin,[97] CXCL8,[170] CXCL13,[45] CCL2,[115] ICAM 2,[123] LTBP2,[123,130] E-selectin, HRG,[131] CD248,[176] VEGF,[170] ADAM17,[1] napsin A,[177] HMGB1,[172] p16,[178] and alveolar NO.[173]
Treatment-related Biomarkers
Serum IGFBP-2 was significantly reduced in patients receiving specific antifibrotic therapy (pirfenidone and nintedanib) compared to untreated patients.[7] Angiogenesis cytokines (bFGF, PLGF, and VEGF-A), anti-inflammatory cytokines (IL-10 and IL-4), and SP-D levels in BALF increased significantly after 6 months of pirfenidone therapy,[121] while Gal-3 levels in BALF appeared to be lower in IPF patients receiving corticosteroid therapy.[95]
Conclusions
HRCT is not always useful for diagnosis due to the presence of other chronic fibrotic lung disorders such as cHP and CTD-ILD. In addition,other idiopathic ILDs may exhibit a UIP-like pattern. This study summarized over 100 differentially expressed biomarkers for patients with IPF compared with HCs, and among these markers, 19 were specific to IPF, which is of great clinical value for the differential diagnosis of IPF. The existing physiological and imaging measurements (pulmonary function tests and HRCT) used to evaluate the occurrence of AE, disease progression, and disease severity present limitations. Pulmonary function tests are influenced by several factors and repeated imaging examination may cause radiation damage to patients. Thus, the present review summarized biomarkers for identifying the onset of AE, for predicting the prognosis of patients, for assessing disease severity, and for predicting the patient's response to treatment to achieve better patient stratification. Combining physiological measurements and biomarkers may increase the accuracy and sensitivity of predictive analysis. With the exception of SP-A, SP-D, and KL-6 which are used in clinical practice in Japan, most other biomarkers are still being evaluated in clinical trials. The biomarkers mentioned in this article are mainly evaluated individually, and the research to evaluate the value of biomarker panels in clinical practice is very limited. The etiology of IPF is complex, and many factors and signal pathways are involved in the pathogenesis of IPF. Thus, a single biomarker is unlikely to have a transformative effect on clinical practice, and therefore, the combined effect of various biomarkers can be considered to improve the accuracy of diagnosis, disease assessment, and monitoring of response to treatment for IPF. Thus, large-scale multicenter studies are needed to design and validate suitable biomarker panels that have diagnostic utility for IPF. The combined application of biomarker panels and physiological and imaging parameters in the diagnosis and treatment of IPF may be a trend in the future.
Funding
This study was supported by the grants from the National Natural Science Foundation of China (Nos. 81970083 and 82170097).
Conflicts of interest
None.
References
1. Wang Q, Xie ZL, Wu Q, Jin ZX, Yang C, Feng J. Role of various imbalances centered on alveolar epithelial cell/fibroblast apoptosis imbalance in the pathogenesis of
idiopathic pulmonary fibrosis.
Chin Med J 2021; 134:261–274. doi: 10.1097/CM9.0000000000001288.
2. Solomon JJ, Chung JH, Cosgrove GP, Demoruelle MK, Fernandez-Perez ER, Fischer A, et al. Predictors of mortality in rheumatoid arthritis-associated interstitial lung disease.
Eur Respir J 2016; 47:588–596. doi: 10.1183/13993003.00357-2015.
3. Morell F, Villar A, Montero MÁ, Muñoz X, Colby TV, Pipvath S, et al. Chronic hypersensitivity pneumonitis in patients diagnosed with
idiopathic pulmonary fibrosis: A prospective case-cohort study.
Lancet Respir Med 2013; 1:685–694. doi: 10.1016/S2213-2600(13)70191-7.
4. Raghu G, Collard HR, Egan JJ, Martinez FJ, Behr J, Brown KK, et al. An official ATS/ERS/JRS/ALAT statement:
Idiopathic pulmonary fibrosis: Evidence-based guidelines for
diagnosis and management.
Am J Respir Crit Care Med 2011; 183:788–824. doi: 10.1164/rccm.2009-040GL.
5. Ohta S, Okamoto M, Fujimoto K, Sakamoto N, Takahashi K, Yamamoto H, et al. The usefulness of monomeric periostin as a
biomarker for
idiopathic pulmonary fibrosis.
PLoS One 2017; 12:e0174547doi: 10.1371/journal.pone.0174547.
6. Hamai K, Iwamoto H, Ishikawa N, Horimasu Y, Masuda T, Miyamoto S, et al. Comparative study of circulating MMP-7, CCL18, KL-6, SP-A, and SP-D as disease markers of
idiopathic pulmonary fibrosis.
Dis Markers 2016; 2016:4759040doi: 10.1155/2016/4759040.
7. Guiot J, Bondue B, Henket M, Corhay JL, Louis R. Raised serum levels of IGFBP-1 and IGFBP-2 in
idiopathic pulmonary fibrosis.
BMC Pulm Med 2016; 16:86doi: 10.1186/s12890-016-0249-6.
8. Raghu G, Richeldi L, Jagerschmidt A, Martin V, Subramaniam A, Ozoux ML, et al.
Idiopathic pulmonary fibrosis: Prospective, case-controlled study of natural history and circulating biomarkers.
Chest 2018; 154:1359–1370. doi: 10.1016/j.chest.2018.08.1083.
9. Guiot J, Henket M, Corhay JL, Moermans C, Louis R. Sputum biomarkers in IPF: Evidence for raised gene expression and protein level of IGFBP-2, IL-8 and MMP-7.
PLoS One 2017; 12:e0171344doi: 10.1371/journal.pone.0171344.
10. Hirasawa Y, Kohno N, Yokoyama A, Inoue Y, Abe M, Hiwada K. KL-6, a human MUC1 mucin, is chemotactic for human fibroblasts.
Am J Respir Cell Mol Biol 1997; 17:501–507. doi: 10.1165/ajrcmb.17.4.2253.
11. Ohshimo S, Yokoyama A, Hattori N, Ishikawa N, Hirasawa Y, Kohno N. KL-6, a human MUC1 mucin, promotes proliferation and survival of lung fibroblasts.
Biochem Biophys Res Commun 2005; 338:1845–1852. doi: 10.1016/j.bbrc.2005.10.144.
12. Takahashi H, Fujishima T, Koba H, Murakami S, Kurokawa K, Shibuya Y, et al. Serum surfactant proteins A and D as prognostic factors in
idiopathic pulmonary fibrosis and their relationship to disease extent.
Am J Respir Crit Care Med 2000; 162 (3 Pt 1):1109–1114. doi: 10.1164/ajrccm.162.3.9910080.
13. Wang K, Ju Q, Cao J, Tang W, Zhang J. Impact of serum SP-A and SP-D levels on comparison and prognosis of
idiopathic pulmonary fibrosis: A systematic review and meta-analysis.
Medicine (Baltimore) 2017; 96:e7083doi: 10.1097/MD.0000000000007083.
14. Phelps DS, Umstead TM, Mejia M, Carrillo G, Pardo A, Selman M. Increased surfactant protein-A levels in patients with newly diagnosed
idiopathic pulmonary fibrosis.
Chest 2004; 125:617–625. doi: 10.1378/chest.125.2.617.
15. Cecchini MJ, Hosein K, Howlett CJ, Joseph M, Mura M. Comprehensive gene expression profiling identifies distinct and overlapping transcriptional profiles in non-specific interstitial pneumonia and
idiopathic pulmonary fibrosis.
Respir Res 2018; 19:153doi: 10.1186/s12931-018-0857-1.
16. Selman M, Pardo A. Role of epithelial cells in
idiopathic pulmonary fibrosis: From innocent targets to serial killers.
Proc Am Thorac Soc 2006; 3:364–372. doi: 10.1513/pats.200601-003TK.
17. Yamaguchi K, Iwamoto H, Mazur W, Miura S, Sakamoto S, Horimasu Y, et al. Reduced endogenous secretory RAGE in blood and bronchoalveolar lavage fluid is associated with poor prognosis in
idiopathic pulmonary fibrosis.
Respir Res 2020; 21:145doi: 10.1186/s12931-020-01410-3.
18. Ishikawa N, Ohlmeier S, Salmenkivi K, Myllärniemi M, Rahman I, Mazur W, et al. Hemoglobin α and β are ubiquitous in the human lung, decline in
idiopathic pulmonary fibrosis but not in COPD.
Respir Res 2010; 11:123doi: 10.1186/1465-9921-11-123.
19. Uchida T, Shirasawa M, Ware LB, Kojima K, Hata Y, Makita K, et al. Receptor for advanced glycation end-products is a marker of type I cell injury in acute lung injury.
Am J Respir Crit Care Med 2006; 173:1008–1015. doi: 10.1164/rccm.200509-1477OC.
20. Zhang Y, Xin Q, Wu Z, Wang C, Wang Y, Wu Q, et al. Application of isobaric tags for relative and absolute quantification (iTRAQ) coupled with two-dimensional liquid chromatography/tandem mass spectrometry in quantitative proteomic analysis for discovery of serum biomarkers for
idiopathic pulmonary fibrosis.
Med Sci Monit 2018; 24:4146–4153. doi: 10.12659/MSM.908702.
21. Bowman BH, Kurosky A. Haptoglobin: The evolutionary product of duplication, unequal crossing over, and point mutation.
Adv Hum Genet 1982; 12:453–454. doi: 10.1007/978-1-4615-8315-8_3.
22. Kawabata H. Transferrin and transferrin receptors update.
Free Radic Biol Med 2019; 133:46–54. doi: 10.1016/j.freeradbiomed.2018.06.037.
23. Allden SJ, Ogger PP, Ghai P, McErlean P, Hewitt R, Toshner R, et al. The transferrin receptor CD71 delineates functionally distinct airway macrophage subsets during
idiopathic pulmonary fibrosis.
Am J Respir Crit Care Med 2019; 200:209–219. doi: 10.1164/rccm.201809-1775OC.
24. Ballester B, Milara J, Cortijo J. Mucins as a new Frontier in pulmonary fibrosis.
J Clin Med 2019; 8:1447doi: 10.3390/jcm8091447.
25. Hattrup CL, Gendler SJ. Structure and function of the cell surface (tethered) mucins.
Annu Rev Physiol 2008; 70:431–457. doi: 10.1146/annurev.physiol.70.113006.100659.
26. Conti C, Montero-Fernandez A, Borg E, Osadolor T, Viola P, De Lauretis A, et al. Mucins MUC5B and MUC5AC in distal airways and honeycomb spaces: Comparison among
idiopathic pulmonary fibrosis/usual interstitial pneumonia, fibrotic nonspecific interstitial pneumonitis, and control lungs.
Am J Respir Crit Care Med 2016; 193:462–464. doi: 10.1164/rccm.201507-1322LE.
27. Nakano Y, Yang IV, Walts AD, Watson AM, Helling BA, Fletcher AA, et al. MUC5B promoter variant rs35705950 affects MUC5B expression in the distal airways in
idiopathic pulmonary fibrosis.
Am J Respir Crit Care Med 2016; 193:464–466. doi: 10.1164/rccm.201509-1872LE.
28. Vietri L, Bennett D, Cameli P, Bergantini L, Cillis G, Sestini P, et al. Serum amyloid A in patients with
idiopathic pulmonary fibrosis.
Respir Investig 2019; 57:430–434. doi: 10.1016/j.resinv.2019.03.010.
29. Lakota K, Carns M, Podlusky S, Mrak-Poljsak K, Hinchcliff M, Lee J, et al. Serum amyloid A is a marker for pulmonary involvement in systemic sclerosis.
PLoS One 2015; 10:e0110820doi: 10.1371/journal.pone.0110820.
30. Pan Y, Fu H, Kong Q, Xiao Y, Shou Q, Chen H, et al. Prevention of pulmonary fibrosis with salvianolic acid a by inducing fibroblast cell cycle arrest and promoting apoptosis.
J Ethnopharmacol 2014; 155:1589–1596. doi: 10.1016/j.jep.2014.07.049.
31. Yamada T. Serum amyloid A (SAA): A concise review of biology, assay methods and clinical usefulness.
Clin Chem Lab Med 1999; 37:381–388. doi: 10.1515/CCLM.1999.063.
32. Cha SI, Ryerson CJ, Lee JS, Kukreja J, Barry SS, Jones KD, et al. Cleaved cytokeratin-18 is a mechanistically informative
biomarker in
idiopathic pulmonary fibrosis.
Respir Res 2012; 13:105doi: 10.1186/1465-9921-13-105.
33. Kono M, Nakamura Y, Oyama Y, Mori K, Hozumi H, Karayama M, et al. Increased levels of serum Wisteria floribunda agglutinin-positive Mac-2 binding protein in
idiopathic pulmonary fibrosis.
Respir Med 2016; 115:46–52. doi: 10.1016/j.rmed.2016.04.013.
34. Hellstern S, Sasaki T, Fauser C, Lustig A, Timpl R, Engel J. Functional studies on recombinant domains of Mac-2-binding protein.
J Biol Chem 2002; 277:15690–15696. doi: 10.1074/jbc.M200386200.
35. Grassadonia A, Tinari N, Iurisci I, Piccolo E, Cumashi A, Innominato P, et al. 90K (Mac-2 BP) and galectins in tumor progression and metastasis.
Glycoconj J 2002; 19:551–556. doi: 10.1023/B:GLYC.0000014085.00706.d4.
36. Kuno A, Ikehara Y, Tanaka Y, Ito K, Matsuda A, Sekiya S, et al. A serum “sweet-doughnut” protein facilitates fibrosis evaluation and therapy assessment in patients with viral hepatitis.
Sci Rep 2013; 3:1065doi: 10.1038/srep01065.
37. Buendía-Roldán I, Ruiz V, Sierra P, Montes E, Ramírez R, Vega A, et al. Increased Expression of CC16 in Patients with
Idiopathic Pulmonary Fibrosis.
PLoS One 2016; 11:e0168552doi: 10.1371/journal.pone.0168552.
38. Ricci A, Mariotta S, Bronzetti E, Bruno P, Vismara L, De Dominicis C, et al. Serum CA 15-3 is increased in pulmonary fibrosis.
Sarcoidosis Vasc Diffuse Lung Dis 2009; 26:54–63.
39. Fahim A, Crooks MG, Wilmot R, Campbell AP, Morice AH, Hart SP. Serum carcinoembryonic antigen correlates with severity of
idiopathic pulmonary fibrosis.
Respirology 2012; 17:1247–1252. doi: 10.1111/j.1440-1843.2012.02231.x.
40. Hadjiliadis D, Tapson VF, Davis RD, Palmer SM. Prognostic value of serum carcinoembryonic antigen levels in patients who undergo lung transplantation.
J Heart Lung Transplant 2001; 20:1305–1309. doi: 10.1016/s1053-2498(01)00373-4.
41. Takahashi H, Nukiwa T, Matsuoka R, Danbara T, Natori H, Arai T, et al. Carcinoembryonic antigen in bronchoalveolar lavage fluid in patients with
idiopathic pulmonary fibrosis.
Jpn J Med 1985; 24:236–243. doi: 10.2169/internalmedicine1962.24.236.
42. Rosas IO, Richards TJ, Konishi K, Zhang Y, Gibson K, Lokshin AE, et al. MMP1 and MMP7 as potential peripheral blood biomarkers in
idiopathic pulmonary fibrosis.
PLoS Med 2008; 5:e93doi: 10.1371/journal.pmed.0050093.
43. Pardo A, Selman M, Kaminski N. Approaching the degradome in
idiopathic pulmonary fibrosis.
Int J Biochem Cell Biol 2008; 40:1141–1155. doi: 10.1016/j.biocel.2007.11.020.
44. Pardo A, Cabrera S, Maldonado M, Selman M. Role of matrix metalloproteinases in the pathogenesis of
idiopathic pulmonary fibrosis.
Respir Res 2016; 17:23doi: 10.1186/s12931-016-0343-6.
45. DePianto DJ, Chandriani S, Abbas AR, Jia G, N’Diaye EN, Caplazi P, et al. Heterogeneous gene expression signatures correspond to distinct lung pathologies and biomarkers of disease severity in
idiopathic pulmonary fibrosis.
Thorax 2015; 70:48–56. doi: 10.1136/thoraxjnl-2013-204596.
46. Yamashita CM, Dolgonos L, Zemans RL, Young SK, Robertson J, Briones N, et al. Matrix metalloproteinase 3 is a mediator of pulmonary fibrosis.
Am J Pathol 2011; 179:1733–1745. doi: 10.1016/j.ajpath.2011.06.041.
47. Kaminski N, Allard JD, Pittet JF, Zuo F, Griffiths MJ, Morris D, et al. Global analysis of gene expression in pulmonary fibrosis reveals distinct programs regulating lung inflammation and fibrosis.
Proc Natl Acad Sci U S A 2000; 97:1778–1783. doi: 10.1073/pnas.97.4.1778.
48. Cabrera S, Selman M, Lonzano-Bolaños A, Konishi K, Richards TJ, Kaminski N, et al. Gene expression profiles reveal molecular mechanisms involved in the progression and resolution of bleomycin-induced lung fibrosis.
Am J Physiol Lung Cell Mol Physiol 2013; 304:L593–L601. doi: 10.1152/ajplung.00320.2012.
49. Tzouvelekis A, Herazo-Maya JD, Slade M, Chu JH, Deiuliis G, Ryu C, et al. Validation of the prognostic value of MMP-7 in
idiopathic pulmonary fibrosis.
Respirology 2017; 22:486–493. doi: 10.1111/resp.12920.
50. Sokai A, Handa T, Tanizawa K, Oga T, Uno K, Tsuruyama T, et al. Matrix metalloproteinase-10: A novel
biomarker for
idiopathic pulmonary fibrosis.
Respir Res 2015; 16:120doi: 10.1186/s12931-015-0280-9.
51. Foster MW, Morrison LD, Todd JL, Snyder LD, Thompson JW, Soderblom EJ, et al. Quantitative proteomics of bronchoalveolar lavage fluid in
idiopathic pulmonary fibrosis.
J Proteome Res 2015; 14:1238–1249. doi: 10.1021/pr501149m.
52. Pardo A, Gibson K, Cisneros J, Richards TJ, Yang Y, Becerril C, et al. Up-regulation and profibrotic role of osteopontin in human
idiopathic pulmonary fibrosis.
PLoS Med 2005; 2:e251doi: 10.1371/journal.pmed.0020251.
53. Imai K, Hiramatsu A, Fukushima D, Pierschbacher MD, Okada Y. Degradation of decorin by matrix metalloproteinases: Identification of the cleavage sites, kinetic analyses and transforming growth factor-beta1 release.
Biochem J 1997; 322 (Pt 3):809–814. doi: 10.1042/bj3220809.
54. Vuorinen K, Myllärniemi M, Lammi L, Piirilä P, Rytilä P, Salmenkivi K, et al. Elevated matrilysin levels in bronchoalveolar lavage fluid do not distinguish
idiopathic pulmonary fibrosis from other interstitial lung diseases.
APMIS 2007; 115:969–975. doi: 10.1111/j.1600-0463.2007.apm_697.x.
55. McKeown S, Richter AG, O’Kane C, McAuley DF, Thickett DR. MMP expression and abnormal lung permeability are important determinants of outcome in IPF.
Eur Respir J 2009; 33:77–84. doi: 10.1183/09031936.00060708.
56. Willems S, Verleden SE, Vanaudenaerde BM, Wynants M, Dooms C, Yserbyt J, et al. Multiplex protein profiling of bronchoalveolar lavage in
idiopathic pulmonary fibrosis and hypersensitivity pneumonitis.
Ann Thorac Med 2013; 8:38–45. doi: 10.4103/1817-1737.105718.
57. Craig VJ, Polverino F, Laucho-Contreras ME, Shi Y, Liu Y, Osorio JC, et al. Mononuclear phagocytes and airway epithelial cells: Novel sources of matrix metalloproteinase-8 (MMP-8) in patients with
idiopathic pulmonary fibrosis.
PLoS One 2014; 9:e97485doi: 10.1371/journal.pone.0097485.
58. García-Prieto E, González-López A, Cabrera S, Astudillo A, Gutiérrez-Fernández A, Fanjul-Fernandez M, et al. Resistance to bleomycin-induced lung fibrosis in MMP-8 deficient mice is mediated by interleukin-10.
PLoS One 2010; 5:e13242doi: 10.1371/journal.pone.0013242.
59. Todd JL, Neely ML, Overton R, Durham K, Gulati M, Huang H, et al. Peripheral blood proteomic profiling of
idiopathic pulmonary fibrosis biomarkers in the multicentre IPF-PRO Registry.
Respir Res 2019; 20:227doi: 10.1186/s12931-019-1190-z.
60. Selman M, Ruiz V, Cabrera S, Segura L, Ramírez R, Barrios R, et al. TIMP-1, -2, -3, and -4 in
idiopathic pulmonary fibrosis. A prevailing nondegradative lung microenvironment?
Am J Physiol Lung Cell Mol Physiol 2000; 279:L562–L574. doi: 10.1152/ajplung.2000.279.3.L562.
61. Maldonado M, Buendía-Roldán I, Vicens-Zygmunt V, Planas L, Molina-Molina M, Selman M, et al. Identification of MMP28 as a
biomarker for the differential
diagnosis of
idiopathic pulmonary fibrosis.
PLoS One 2018; 13:e0203779doi: 10.1371/journal.pone.0203779.
62. Maldonado M, Salgado-Aguayo A, Herrera I, Cabrera S, Ortíz-Quintero B, Staab-Weijnitz CA, et al. Upregulation and nuclear location of MMP28 in alveolar epithelium of
idiopathic pulmonary fibrosis.
Am J Respir Cell Mol Biol 2018; 59:77–86. doi: 10.1165/rcmb.2017-0223OC.
63. Okamoto M, Izuhara K, Ohta S, Ono J, Hoshino T. Ability of periostin as a new
biomarker of
idiopathic pulmonary fibrosis.
Adv Exp Med Biol 2019; 1132:79–87. doi: 10.1007/978-981-13-6657-4_9.
64. Okamoto M, Hoshino T, Kitasato Y, Sakazaki Y, Kawayama T, Fujimoto K, et al. Periostin, a matrix protein, is a novel
biomarker for idiopathic interstitial pneumonias.
Eur Respir J 2011; 37:1119–1127. doi: 10.1183/09031936.00059810.
65. Uchida M, Shiraishi H, Ohta S, Arima K, Taniguchi K, Suzuki S, et al. Periostin, a matricellular protein, plays a role in the induction of chemokines in pulmonary fibrosis.
Am J Respir Cell Mol Biol 2012; 46:677–686. doi: 10.1165/rcmb.2011-0115OC.
66. Naik PK, Bozyk PD, Bentley JK, Popova AP, Birch CM, Wilke CA, et al. Periostin promotes fibrosis and predicts progression in patients with
idiopathic pulmonary fibrosis.
Am J Physiol Lung Cell Mol Physiol 2012; 303:L1046–L1056. doi: 10.1152/ajplung.00139.2012.
67. Ashley SL, Wilke CA, Kim KK, Moore BB. Periostin regulates fibrocyte function to promote myofibroblast differentiation and lung fibrosis.
Mucosal Immunol 2017; 10:341–351. doi: 10.1038/mi.2016.61.
68. Strieter RM, Mehrad B. New mechanisms of pulmonary fibrosis.
Chest 2009; 136:1364–1370. doi: 10.1378/chest.09-0510.
69. Desai B, Mattson J, Paintal H, Nathan M, Shen F, Beaumont M, et al. Differential expression of monocyte/macrophage- selective markers in human
idiopathic pulmonary fibrosis.
Exp Lung Res 2011; 37:227–238. doi: 10.3109/01902148.2010.538132.
70. Takahashi F, Takahashi K, Okazaki T, Maeda K, Ienaga H, Maeda M, et al. Role of osteopontin in the pathogenesis of bleomycin-induced pulmonary fibrosis.
Am J Respir Cell Mol Biol 2001; 24:264–271. doi: 10.1165/ajrcmb.24.3.4293.
71. Lee SH, Seo GS, Park YN, Yoo TM, Sohn DH. Effects and regulation of osteopontin in rat hepatic stellate cells.
Biochem Pharmacol 2004; 68:2367–2378. doi: 10.1016/j.bcp.2004.08.022.
72. Ota C, Ng-Blichfeldt JP, Korfei M, Alsafadi HN, Lehmann M, Skronska-Wasek W, et al. Dynamic expression of HOPX in alveolar epithelial cells reflects injury and repair during the progression of pulmonary fibrosis.
Sci Rep 2018; 8:12983doi: 10.1038/s41598-018-31214-x.
73. Korfei M, Schmitt S, Ruppert C, Henneke I, Markart P, Loeh B, et al. Comparative proteomic analysis of lung tissue from patients with
idiopathic pulmonary fibrosis (IPF) and lung transplant donor lungs.
J Proteome Res 2011; 10:2185–2205. doi: 10.1021/pr1009355.
74. Myllärniemi M, Tikkanen J, Hulmi JJ, Pasternack A, Sutinen E, Rönty M, et al. Upregulation of activin-B and follistatin in pulmonary fibrosis - a translational study using human biopsies and a specific inhibitor in mouse fibrosis models.
BMC Pulm Med 2014; 14:170doi: 10.1186/1471-2466-14-170.
75. Ziora D, Jastrzębski D, Adamek M, Czuba Z, Kozielski JJ, Grzanka A, et al. Circulating concentration of markers of angiogenic activity in patients with sarcoidosis and
idiopathic pulmonary fibrosis.
BMC Pulm Med 2015; 15:113doi: 10.1186/s12890-015-0110-3.
76. Jaffar J, Unger S, Corte TJ, Keller M, Wolters PJ, Richeldi L, et al. Fibulin-1 predicts disease progression in patients with
idiopathic pulmonary fibrosis.
Chest 2014; 146:1055–1063. doi: 10.1378/chest.13-2688.
77. Roark EF, Keene DR, Haudenschild CC, Godyna S, Little CD, Argraves WS. The association of human fibulin-1 with elastic fibers: An immunohistological, ultrastructural, and RNA study.
J Histochem Cytochem 1995; 43:401–411. doi: 10.1177/43.4.7534784.
78. Ruiz XD, Mlakar LR, Yamaguchi Y, Su Y, Larregina AT, Pilewski JM, et al. Syndecan-2 is a novel target of insulin-like growth factor binding protein-3 and is over-expressed in fibrosis.
PLoS One 2012; 7:e43049doi: 10.1371/journal.pone.0043049.
79. Furuhashi K, Suda T, Nakamura Y, Inui N, Hashimoto D, Miwa S, et al. Increased expression of YKL-40, a chitinase-like protein, in serum and lung of patients with
idiopathic pulmonary fibrosis.
Respir Med 2010; 104:1204–1210. doi: 10.1016/j.rmed.2010.02.026.
80. Korthagen NM, van Moorsel CH, Zanen P, Ruven HJ, Grutters JC. Evaluation of circulating YKL-40 levels in idiopathic interstitial pneumonias.
Lung 2014; 192:975–980. doi: 10.1007/s00408-014-9647-9.
81. Korthagen NM, van Moorsel CH, Barlo NP, Ruven HJ, Kruit A, Heron M, et al. Serum and BALF YKL-40 levels are predictors of survival in
idiopathic pulmonary fibrosis.
Respir Med 2011; 105:106–113. doi: 10.1016/j.rmed.2010.09.012.
82. Parsanejad R, Fields WR, Morgan WT, Bombick BR, Doolittle DJ. The time course of expression of genes involved in specific pathways in normal human bronchial epithelial cells following exposure to cigarette smoke.
Exp Lung Res 2008; 34:513–530. doi: 10.1080/01902140802271826.
83. Celada LJ, Kropski JA, Herazo-Maya JD, Luo W, Creecy A, Abad AT, et al. PD-1 up-regulation on CD4
+ T cells promotes pulmonary fibrosis through STAT3-mediated IL-17A and TGF-β1 production.
Sci Transl Med 2018; 10:eaar8356doi: 10.1126/scitranslmed.aar8356.
84. Landi C, Bargagli E, Bianchi L, Gagliardi A, Carleo A, Bennett D, et al. Towards a functional proteomics approach to the comprehension of
idiopathic pulmonary fibrosis, sarcoidosis, systemic sclerosis and pulmonary Langerhans cell histiocytosis.
J Proteomics 2013; 83:60–75. doi: 10.1016/j.jprot.2013.03.006.
85. Hara A, Sakamoto N, Ishimatsu Y, Kakugawa T, Nakashima S, Hara S, et al. S100A9 in BALF is a candidate
biomarker of
idiopathic pulmonary fibrosis.
Respir Med 2012; 106:571–580. doi: 10.1016/j.rmed.2011.12.010.
86. Korthagen NM, Nagtegaal MM, van Moorsel CH, Kazemier KM, van den Bosch JM, Grutters JC. MRP14 is elevated in the bronchoalveolar lavage fluid of fibrosing interstitial lung diseases.
Clin Exp Immunol 2010; 161:342–347. doi: 10.1111/j.1365-2249.2010.04181.x.
87. Richards TJ, Kaminski N, Baribaud F, Flavin S, Brodmerkel C, Horowitz D, et al. Peripheral blood proteins predict mortality in
idiopathic pulmonary fibrosis.
Am J Respir Crit Care Med 2012; 185:67–76. doi: 10.1164/rccm.201101-0058OC.
88. Ryckman C, McColl SR, Vandal K, de Médicis R, Lussier A, Poubelle PE, et al. Role of S100A8 and S100A9 in neutrophil recruitment in response to monosodium urate monohydrate crystals in the air-pouch model of acute gouty arthritis.
Arthritis Rheum 2003; 48:2310–2320. doi: 10.1002/art.11079.
89. Ryckman C, Vandal K, Rouleau P, Talbot M, Tessier PA. Proinflammatory activities of S100: Proteins S100A8, S100A9, and S100A8/A9 induce neutrophil chemotaxis and adhesion.
J Immunol 2003; 170:3233–3242. doi: 10.4049/jimmunol.170.6.3233.
90. Kinder BW, Brown KK, Schwarz MI, Ix JH, Kervitsky A, King TE Jr. Baseline BAL neutrophilia predicts early mortality in
idiopathic pulmonary fibrosis.
Chest 2008; 133:226–232. doi: 10.1378/chest.07-1948.
91. Shibata F, Miyama K, Shinoda F, Mizumoto J, Takano K, Nakagawa H. Fibroblast growth-stimulating activity of S100A9 (MRP-14).
Eur J Biochem 2004; 271:2137–2143. doi: 10.1111/j.1432-1033.2004.04129.x.
92. Meneghin A, Choi ES, Evanoff HL, Kunkel SL, Martinez FJ, Flaherty KR, et al. TLR9 is expressed in idiopathic interstitial pneumonia and its activation promotes in vitro myofibroblast differentiation.
Histochem Cell Biol 2008; 130:979–992. doi: 10.1007/s00418-008-0466-z.
93. Trujillo G, Meneghin A, Flaherty KR, Sholl LM, Myers JL, Kazerooni EA, et al. TLR9 differentiates rapidly from slowly progressing forms of
idiopathic pulmonary fibrosis.
Sci Transl Med 2010; 2:57ra82doi: 10.1126/scitranslmed.3001510.
94. Bennett D, Bargagli E, Bianchi N, Landi C, Fossi A, Fui A, et al. Elevated level of Galectin-1 in bronchoalveolar lavage of patients with
idiopathic pulmonary fibrosis.
Respir Physiol Neurobiol 2020; 273:103323doi: 10.1016/j.resp.2019.103323.
95. Nishi Y, Sano H, Kawashima T, Okada T, Kuroda T, Kikkawa K, et al. Role of galectin-3 in human pulmonary fibrosis.
Allergol Int 2007; 56:57–65. doi: 10.2332/allergolint.O-06-449.
96. Abebayehu D, Spence A, Boyan BD, Schwartz Z, Ryan JJ, McClure MJ. Galectin-1 promotes an M2 macrophage response to polydioxanone scaffolds.
J Biomed Mater Res A 2017; 105:2562–2571. doi: 10.1002/jbm.a.36113.
97. Mukae H, Iiboshi H, Nakazato M, Hiratsuka T, Tokojima M, Abe K, et al. Raised plasma concentrations of alpha-defensins in patients with
idiopathic pulmonary fibrosis.
Thorax 2002; 57:623–628. doi: 10.1136/thorax.57.7.623.
98. Mukae H, Ishimoto H, Yanagi S, Ishii H, Nakayama S, Ashitani J, et al. Elevated BALF concentrations of alpha- and beta-defensins in patients with pulmonary alveolar proteinosis.
Respir Med 2007; 101:715–721. doi: 10.1016/j.rmed.2006.08.018.
99. Hiratsuka T, Mukae H, Iiboshi H, Ashitani J, Nabeshima K, Minematsu T, et al. Increased concentrations of human beta-defensins in plasma and bronchoalveolar lavage fluid of patients with diffuse panbronchiolitis.
Thorax 2003; 58:425–430. doi: 10.1136/thorax.58.5.425.
100. Kasabova M, Joulin-Giet A, Lecaille F, Saidi A, Marchand-Adam S, Lalmanach G. Human cystatin C: A new
biomarker of
idiopathic pulmonary fibrosis?
Proteomics Clin Appl 2014; 8:447–453. doi: 10.1002/prca.201300047.
101. Saini G, Porte J, Weinreb PH, Violette SM, Wallace WA, McKeever TM, et al. αvβ6 integrin may be a potential prognostic
biomarker in interstitial lung disease.
Eur Respir J 2015; 46:486–494. doi: 10.1183/09031936.00210414.
102. Madala SK, Korfhagen TR, Schmidt S, Davidson C, Edukulla R, Ikegami M, et al. Inhibition of the αvβ6 integrin leads to limited alteration of TGF-α-induced pulmonary fibrosis.
Am J Physiol Lung Cell Mol Physiol 2014; 306:L726–L735. doi: 10.1152/ajplung.00357.2013.
103. Agrez M, Chen A, Cone RI, Pytela R, Sheppard D. The alpha v beta 6 integrin promotes proliferation of colon carcinoma cells through a unique region of the beta 6 cytoplasmic domain.
J Cell Biol 1994; 127:547–556. doi: 10.1083/jcb.127.2.547.
104. Huang X, Wu J, Spong S, Sheppard D. The integrin alphavbeta6 is critical for keratinocyte migration on both its known ligand, fibronectin, and on vitronectin.
J Cell Sci 1998; 111 (Pt 15):2189–2195. doi: 10.1242/jcs.111.15.2189.
105. Thomas GJ, Lewis MP, Hart IR, Marshall JF, Speight PM. AlphaVbeta6 integrin promotes invasion of squamous carcinoma cells through up-regulation of matrix metalloproteinase-9.
Int J Cancer 2001; 92:641–650. doi: 10.1002/1097-0215(20010601)92:5<641:aid-ijc1243>3.0.co;2-p.
106. Kahloon RA, Xue J, Bhargava A, Csizmadia E, Otterbein L, Kass DJ, et al. Patients with
idiopathic pulmonary fibrosis with antibodies to heat shock protein 70 have poor prognoses.
Am J Respir Crit Care Med 2013; 187:768–775. doi: 10.1164/rccm.201203-0506OC.
107. Mayadas TN, Tsokos GC, Tsuboi N. Mechanisms of immune complex-mediated neutrophil recruitment and tissue injury.
Circulation 2009; 120:2012–2024. doi: 10.1161/CIRCULATIONAHA.108.771170.
108. Collard HR, Moore BB, Flaherty KR, Brown KK, Kaner RJ, King TE Jr, et al. Acute exacerbations of
idiopathic pulmonary fibrosis.
Am J Respir Crit Care Med 2007; 176:636–643. doi: 10.1164/rccm.200703-463PP.
109. Gui X, Qiu X, Tian Y, Xie M, Li H, Gao Y, et al. Prognostic value of IFN-γ, sCD163, CCL2 and CXCL10 involved in acute exacerbation of
idiopathic pulmonary fibrosis.
Int Immunopharmacol 2019; 70:208–215. doi: 10.1016/j.intimp.2019.02.039.
110. Vuga LJ, Tedrow JR, Pandit KV, Tan J, Kass DJ, Xue J, et al. C-X-C motif chemokine 13 (CXCL13) is a prognostic
biomarker of
idiopathic pulmonary fibrosis.
Am J Respir Crit Care Med 2014; 189:966–974. doi: 10.1164/rccm.201309-1592OC.
111. Jia G, Chandriani S, Abbas AR, DePianto DJ, N’Diaye EN, Yaylaoglu MB, et al. CXCL14 is a candidate
biomarker for hedgehog signalling in
idiopathic pulmonary fibrosis.
Thorax 2017; 72:780–787. doi: 10.1136/thoraxjnl-2015-207682.
112. Agostini C, Facco M, Siviero M, Carollo D, Galvan S, Cattelan AM, et al. CXC chemokines IP-10 and mig expression and direct migration of pulmonary CD8+/CXCR3+ T cells in the lungs of patients with HIV infection and T-cell alveolitis.
Am J Respir Crit Care Med 2000; 162 (4 Pt 1):1466–1473. doi: 10.1164/ajrccm.162.4.2003130.
113. Hu B, Liu J, Wu Z, Liu T, Ullenbruch MR, Ding L, et al. Reemergence of hedgehog mediates epithelial-mesenchymal crosstalk in pulmonary fibrosis.
Am J Respir Cell Mol Biol 2015; 52:418–428. doi: 10.1165/rcmb.2014-0108OC.
114. Chandriani S, DePianto DJ, N’Diaye EN, Abbas AR, Jackman J, Bevers J 3rd, et al. Endogenously expressed IL-13Rα2 attenuates IL-13-mediated responses but does not activate signaling in human lung fibroblasts.
J Immunol 2014; 193:111–119. doi: 10.4049/jimmunol.1301761.
115. Capelli A, Di Stefano A, Gnemmi I, Donner CF. CCR5 expression and CC chemokine levels in
idiopathic pulmonary fibrosis.
Eur Respir J 2005; 25:701–707. doi: 10.1183/09031936.05.00082604.
116. Baran CP, Opalek JM, McMaken S, Newland CA, O’Brien JM Jr, Hunter MG, et al. Important roles for macrophage colony-stimulating factor, CC chemokine ligand 2, and mononuclear phagocytes in the pathogenesis of pulmonary fibrosis.
Am J Respir Crit Care Med 2007; 176:78–89. doi: 10.1164/rccm.200609-1279OC.
117. Wynn TA, Vannella KM. Macrophages in Tissue Repair, Regeneration, and Fibrosis.
Immunity 2016; 44:450–462. doi: 10.1016/j.immuni.2016.02.015.
118. Yao Y, Wang Y, Zhang Z, He L, Zhu J, Zhang M, et al. Chop Deficiency Protects Mice Against Bleomycin-induced Pulmonary Fibrosis by Attenuating M2 Macrophage Production.
Mol Ther 2016; 24:915–925. doi: 10.1038/mt.2016.36.
119. Zhu Z, Ma B, Zheng T, Homer RJ, Lee CG, Charo IF, et al. IL-13-induced chemokine responses in the lung: Role of CCR2 in the pathogenesis of IL-13-induced inflammation and remodeling.
J Immunol 2002; 168:2953–2962. doi: 10.4049/jimmunol.168.6.2953.
120. Hamada K, Nagai S, Tanaka S, Handa T, Shigematsu M, Nagao T, et al. Significance of pulmonary arterial pressure and diffusion capacity of the lung as prognosticator in patients with
idiopathic pulmonary fibrosis.
Chest 2007; 131:650–656. doi: 10.1378/chest.06-1466.
121. Ronan N, Bennett DM, Khan KA, McCarthy Y, Dahly D, Bourke L, et al. Tissue and Bronchoalveolar Lavage Biomarkers in
Idiopathic Pulmonary Fibrosis Patients on Pirfenidone.
Lung 2018; 196:543–552. doi: 10.1007/s00408-018-0140-8.
122. Ley B, Brown KK, Collard HR. Molecular biomarkers in
idiopathic pulmonary fibrosis.
Am J Physiol Lung Cell Mol Physiol 2014; 307:L681–L691. doi: 10.1152/ajplung.00014.2014.
123. Tsoutsou PG, Gourgoulianis KI, Petinaki E, Mpaka M, Efremidou S, Maniatis A, et al. ICAM-1, ICAM-2 and ICAM-3 in the sera of patients with
idiopathic pulmonary fibrosis.
Inflammation 2004; 28:359–364. doi: 10.1007/s10753-004-6647-6.
124. O’Dwyer DN, Norman KC, Xia M, Huang Y, Gurczynski SJ, Ashley SL, et al. The peripheral blood proteome signature of
idiopathic pulmonary fibrosis is distinct from normal and is associated with novel immunological processes.
Sci Rep 2017; 7:46560doi: 10.1038/srep46560.
125. Nakao A, Hasegawa Y, Tsuchiya Y, Shimokata K. Expression of cell adhesion molecules in the lungs of patients with
idiopathic pulmonary fibrosis.
Chest 1995; 108:233–239. doi: 10.1378/chest.108.1.233.
126. Hayashi S, Abe K, Matsuoka H, Goya S, Morishita H, Mori M, et al. Increased level of soluble E-selectin in the serum from patients with
idiopathic pulmonary fibrosis.
Inflammation 2004; 28:1–5. doi: 10.1023/b:ifla.0000014705.11961.c7.
127. Chadelat K, Boule M, Corroyer S, Fauroux B, Delaisi B, Tournier G, et al. Expression of insulin-like growth factors and their binding proteins by bronchoalveolar cells from children with and without interstitial lung disease.
Eur Respir J 1998; 11:1329–1336. doi: 10.1183/09031936.98.11061329.
128. Pilewski JM, Liu L, Henry AC, Knauer AV, Feghali-Bostwick CA. Insulin-like growth factor binding proteins 3 and 5 are overexpressed in
idiopathic pulmonary fibrosis and contribute to extracellular matrix deposition.
Am J Pathol 2005; 166:399–407. doi: 10.1016/S0002-9440(10)62263-8.
129. Vuga LJ, Milosevic J, Pandit K, Ben-Yehudah A, Chu Y, Richards T, et al. Cartilage oligomeric matrix protein in
idiopathic pulmonary fibrosis.
PLoS One 2013; 8:e83120doi: 10.1371/journal.pone.0083120.
130. Enomoto Y, Matsushima S, Shibata K, Aoshima Y, Yagi H, Meguro S, et al. LTBP2 is secreted from lung myofibroblasts and is a potential
biomarker for
idiopathic pulmonary fibrosis.
Clin Sci (Lond) 2018; 132:1565–1580. doi: 10.1042/CS20180435.
131. Ernst G, Dantas E, Sabatté J, Caro F, Salvado A, Grynblat P, et al. Histidine-rich glycoprotein and
idiopathic pulmonary fibrosis.
Respir Med 2015; 109:1589–1591. doi: 10.1016/j.rmed.2015.10.010.
132. Cedervall J, Zhang Y, Ringvall M, Thulin A, Moustakas A, Jahnen-Dechent W, et al. HRG regulates tumor progression, epithelial to mesenchymal transition and metastasis via platelet-induced signaling in the pre-tumorigenic microenvironment.
Angiogenesis 2013; 16:889–902. doi: 10.1007/s10456-013-9363-8.
133. Hung CF, Rohani MG, Lee SS, Chen P, Schnapp LM. Role of IGF-1 pathway in lung fibroblast activation.
Respir Res 2013; 14:102doi: 10.1186/1465-9921-14-102.154.
134. Garrett SM, Hsu E, Thomas JM, Pilewski JM, Feghali-Bostwick C. Insulin-like growth factor (IGF)-II- mediated fibrosis in pathogenic lung conditions.
PLoS One 2019; 14:e0225422doi:10.1371/journal.pone.0225422.
135. Koyama S, Sato E, Haniuda M, Numanami H, Nagai S, Izumi T. Decreased level of vascular endothelial growth factor in bronchoalveolar lavage fluid of normal smokers and patients with pulmonary fibrosis.
Am J Respir Crit Care Med 2002; 166:382–385. doi: 10.1164/rccm.2103112.
136. Cosgrove GP, Brown KK, Schiemann WP, Serls AE, Parr JE, Geraci MW, et al. Pigment epithelium-derived factor in
idiopathic pulmonary fibrosis: A role in aberrant angiogenesis.
Am J Respir Crit Care Med 2004; 170:242–251. doi: 10.1164/rccm.200308-1151OC.
137. Gharaee-Kermani M, Denholm EM, Phan SH. Costimulation of fibroblast collagen and transforming growth factor beta1 gene expression by monocyte chemoattractant protein-1 via specific receptors.
J Biol Chem 1996; 271:17779–17784. doi: 10.1074/jbc.271.30.17779.
138. Grotendorst GR, Okochi H, Hayashi N. A novel transforming growth factor beta response element controls the expression of the connective tissue growth factor gene.
Cell Growth Differ 1996; 7:469–480.
139. Inoue Y, King TE Jr, Barker E, Daniloff E, Newman LS. Basic fibroblast growth factor and its receptors in
idiopathic pulmonary fibrosis and lymphangioleiomyomatosis.
Am J Respir Crit Care Med 2002; 166:765–773. doi: 10.1164/rccm.2010014.
140. Itoh S, Itoh F, Goumans MJ, Ten Dijke P. Signaling of transforming growth factor-beta family members through Smad proteins.
Eur J Biochem 2000; 267:6954–6967. doi: 10.1046/j.1432-1327.2000.01828.x.
141. Ohga E, Matsuse T, Teramoto S, Katayama H, Nagase T, Fukuchi Y, et al. Effects of activin A on proliferation and differentiation of human lung fibroblasts.
Biochem Biophys Res Commun 1996; 228:391–396. doi: 10.1006/bbrc.1996.1672.
142. Mills R, Mathur A, Nicol LM, Walker JJ, Przybylski AA, Mackinnon AC, et al. Intrapulmonary autoantibodies to HSP72 are associated with improved outcomes in IPF.
J Immunol Res 2019; 2019:1845128doi: 10.1155/2019/1845128.
143. Wang G, Jiao H, Zheng JN, Sun X. HSP27 regulates TGF-β mediated lung fibroblast differentiation through the Smad3 and ERK pathways.
Int J Mol Med 2017; 39:183–190. doi: 10.3892/ijmm.2016.2813.
144. Sontake V, Wang Y, Kasam RK, Sinner D, Reddy GB, Naren AP, et al. Hsp90 regulation of fibroblast activation in pulmonary fibrosis.
JCI Insight 2017; 2:e91454doi: 10.1172/jci.insight.91454.
145. Nielsen MJ, Madsen M, Møller HJ, Moestrup SK. The macrophage scavenger receptor CD163: Endocytic properties of cytoplasmic tail variants.
J Leukoc Biol 2006; 79:837–845. doi: 10.1189/jlb.1005602.
146. Davis BH, Zarev PV. Human monocyte CD163 expression inversely correlates with soluble CD163 plasma levels.
Cytometry B Clin Cytom 2005; 63:16–22. doi: 10.1002/cyto.b.20031.
147. Aoshiba K, Yasui S, Tamaoki J, Nagai A. The Fas/Fas-ligand system is not required for bleomycin-induced pulmonary fibrosis in mice.
Am J Respir Crit Care Med 2000; 162 (2 Pt 1):695–700. doi: 10.1164/ajrccm.162.2.9907012.
148. Fernandez IE, Eickelberg O. The impact of TGF-β on lung fibrosis: From targeting to biomarkers.
Proc Am Thorac Soc 2012; 9:111–116. doi: 10.1513/pats.201203-023AW.
149. Wynn TA. Integrating mechanisms of pulmonary fibrosis.
J Exp Med 2011; 208:1339–1350. doi: 10.1084/jem.20110551.
150. Moodley YP, Caterina P, Scaffidi AK, Misso NL, Papadimitriou JM, McAnulty RJ, et al. Comparison of the morphological and biochemical changes in normal human lung fibroblasts and fibroblasts derived from lungs of patients with
idiopathic pulmonary fibrosis during FasL-induced apoptosis.
J Pathol 2004; 202:486–495. doi: 10.1002/path.1531.
151. Hao Z, Hampel B, Yagita H. Rajewsky K. cell-specific ablation of Fas leads to Fas ligand-mediated lymphocyte depletion and inflammatory pulmonary fibrosis.
J Exp Med 2004; 199:1355–1365. doi: 10.1084/jem.20032196.
152. Wolters PJ, Blackwell TS, Eickelberg O, Loyd JE, Kaminski N, Jenkins G, et al. Time for a change: Is
idiopathic pulmonary fibrosis still idiopathic and only fibrotic?
Lancet Respir Med 2018; 6:154–160. doi: 10.1016/S2213-2600(18)30007-9.
153. Gauldie J. Pro: Inflammatory mechanisms are a minor component of the pathogenesis of
idiopathic pulmonary fibrosis.
Am J Respir Crit Care Med 2002; 165:1205–1206. doi: 10.1164/rccm.2202054.
154. Seibold MA, Smith RW, Urbanek C, Groshong SD, Cosgrove GP, Brown KK, et al. The
idiopathic pulmonary fibrosis honeycomb cyst contains a mucocilary pseudostratified epithelium.
PLoS One 2013; 8:e58658doi: 10.1371/journal.pone.0058658.
155. Todd NW, Scheraga RG, Galvin JR, Iacono AT, Britt EJ, Luzina IG, et al. Lymphocyte aggregates persist and accumulate in the lungs of patients with
idiopathic pulmonary fibrosis.
J Inflamm Res 2013; 6:63–70. doi: 10.2147/JIR.S40673.
156. White ES, Xia M, Murray S, Dyal R, Flaherty CM, Flaherty KR, et al. Plasma surfactant protein-D, matrix metalloproteinase-7, and osteopontin index distinguishes
idiopathic pulmonary fibrosis from other idiopathic interstitial pneumonias.
Am J Respir Crit Care Med 2016; 194:1242–1251. doi: 10.1164/rccm.201505-0862OC.
157. Bargagli E, Olivieri C, Prasse A, Bianchi N, Magi B, Cianti R, et al. Calgranulin B (S100A9) levels in bronchoalveolar lavage fluid of patients with interstitial lung diseases.
Inflammation 2008; 31:351–354. doi: 10.1007/s10753-008-9085-z.
158. Cameli P, Bargagli E, Bergantini L, Refini RM, Pieroni M, Sestini P, et al. Evaluation of multiple-flows exhaled nitric oxide in idiopathic and non-idiopathic interstitial lung disease.
J Breath Res 2019; 13:026008doi: 10.1088/1752-7163/ab0233.
159. Collard HR, Ryerson CJ, Corte TJ, Jenkins G, Kondoh Y, Lederer DJ, et al. Acute exacerbation of
idiopathic pulmonary fibrosis. An International Working Group Report.
Am J Respir Crit Care Med 2016; 194:265–275. doi: 10.1164/rccm.201604-0801CI.
160. Hanaka T, Kido T, Noguchi S, Yamada S, Noguchi H, Guo X, et al. The overexpression of peroxiredoxin-4 affects the progression of
idiopathic pulmonary fibrosis.
BMC Pulm Med 2019; 19:265doi: 10.1186/s12890-019-1032-2.
161. Cao M, Swigris JJ, Wang X, Cao M, Qiu Y, Huang M, et al. Plasma leptin is elevated in acute exacerbation of
idiopathic pulmonary fibrosis.
Mediators Inflamm 2016; 2016:6940480doi: 10.1155/2016/6940480.
162. Kakugawa T, Yokota S, Ishimatsu Y, Hayashi T, Nakashima S, Hara S, et al. Serum heat shock protein 47 levels are elevated in acute exacerbation of
idiopathic pulmonary fibrosis.
Cell Stress Chaperones 2013; 18:581–590. doi: 10.1007/s12192-013-0411-5.
163. Carleo A, Landi C, Prasse A, Bergantini L, D’Alessandro M, Cameli P, et al. Proteomic characterization of
idiopathic pulmonary fibrosis patients: Stable versus acute exacerbation.
Monaldi Arch Chest Dis 2020; 90:180–190. doi: 10.4081/monaldi.2020.1231.
164. Konishi K, Gibson KF, Lindell KO, Richards TJ, Zhang Y, Dhir R, et al. Gene expression profiles of acute exacerbations of
idiopathic pulmonary fibrosis.
Am J Respir Crit Care Med 2009; 180:167–175. doi: 10.1164/rccm.200810-1596OC.
165. Papiris SA, Tomos IP, Karakatsani A, Spathis A, Korbila I, Analitis A, et al. High levels of IL-6 and IL-8 characterize early-on
idiopathic pulmonary fibrosis acute exacerbations.
Cytokine 2018; 102:168–172. doi: 10.1016/j.cyto.2017.08.019.
166. Schupp JC, Binder H, Jäger B, Cillis G, Zissel G, Müller-Quernheim J, et al. Macrophage activation in acute exacerbation of
idiopathic pulmonary fibrosis.
PLoS One 2015; 10:e0116775doi: 10.1371/journal.pone.0116775.
167. Ebina M, Taniguchi H, Miyasho T, Yamada S, Shibata N, Ohta H, et al. Gradual increase of high mobility group protein b1 in the lungs after the onset of acute exacerbation of
idiopathic pulmonary fibrosis.
Pulm Med 2011; 2011:916486doi: 10.1155/2011/916486.
168. Maher TM, Oballa E, Simpson JK, Porte J, Habgood A, Fahy WA, et al. An epithelial
biomarker signature for
idiopathic pulmonary fibrosis: An analysis from the multicentre PROFILE cohort study.
Lancet Respir Med 2017; 5:946–955. doi: 10.1016/S2213-2600(17)30430-7.
169. Neighbors M, Cabanski CR, Ramalingam TR, Sheng XR, Tew GW, Gu C, et al. Prognostic and predictive biomarkers for patients with
idiopathic pulmonary fibrosis treated with pirfenidone: Post-hoc assessment of the CAPACITY and ASCEND trials.
Lancet Respir Med 2018; 6:615–626. doi: 10.1016/S2213-2600(18)30185-1.
170. Simler NR, Brenchley PE, Horrocks AW, Greaves SM, Hasleton PS, Egan JJ. Angiogenic cytokines in patients with idiopathic interstitial pneumonia.
Thorax 2004; 59:581–585. doi: 10.1136/thx.2003.009860.
171. Hachisu Y, Murata K, Takei K, Tsuchiya T, Tsurumaki H, Koga Y, et al. Possible serological markers to predict mortality in acute exacerbation of
idiopathic pulmonary fibrosis.
Medicina (Kaunas) 2019; 55:132doi: 10.3390/medicina55050132.
172. Yamaguchi K, Iwamoto H, Sakamoto S, Horimasu Y, Masuda T, Miyamoto S, et al. Serum high-mobility group box 1 is associated with the onset and severity of acute exacerbation of
idiopathic pulmonary fibrosis.
Respirology 2020; 25:275–280. doi: 10.1111/resp.13634.
173. Cameli P, Bergantini L, Salvini M, Refini RM, Pieroni M, Bargagli E, et al. Alveolar concentration of nitric oxide as a prognostic
biomarker in
idiopathic pulmonary fibrosis.
Nitric Oxide 2019; 89:41–45. doi: 10.1016/j.niox.2019.05.001.
174. Ge J, Tang L, Mu P, Zhu F, Xie L, Tang Y. Association of ADAM17 expression levels in patients with interstitial lung disease.
Immunol Invest 2020; 49:134–145. doi: 10.1080/08820139.2019.1660367.
175. Su Y, Gu H, Weng D, Zhou Y, Li Q, Zhang F, et al. Association of serum levels of laminin, type IV collagen, procollagen III N-terminal peptide, and hyaluronic acid with the progression of interstitial lung disease.
Medicine (Baltimore) 2017; 96:e6617doi: 10.1097/MD.0000000000006617.
176. Bartis D, Crowley LE, D'Souza VK, Borthwick L, Fisher AJ, Croft AP, et al. Role of CD248 as a potential severity marker in
idiopathic pulmonary fibrosis.
BMC Pulm Med 2016; 16:51doi: 10.1186/s12890-016-0211-7.
177. Samukawa T, Hamada T, Uto H, Yanagi M, Tsukuya G, Nosaki T, et al. The elevation of serum napsin A in
idiopathic pulmonary fibrosis, compared with KL-6, surfactant protein-A and surfactant protein-D.
BMC Pulm Med 2012; 12:55doi: 10.1186/1471-2466-12-55.
178. Schafer MJ, White TA, Iijima K, Haak AJ, Ligresti G, Atkinson EJ, et al. Cellular senescence mediates fibrotic pulmonary disease.
Nat Commun 2017; 8:14532doi: 10.1038/ncomms14532.
