Cytokines amplify and direct the generation of appropriate patterns of immunity to combat particular microbial threats. These same cytokines can cause host tissue injury if the activation/amplification of host defense is overexuberant, as occurs in some infective and sterile forms of inflammation. These pathologic cytokine-driven outcomes are seen in many types of AKI caused by physical, drug, chemical, and ischemic injury. If immune tolerance is lost and host tissue antigens become autoimmune targets, cytokines can direct and mediate inflammatory autoimmune diseases. Important renal examples are the autoimmune forms of inflammatory/crescentic GN. Cytokines act in concert to generate inflammation in host defense and disease, but some cytokines attenuate inflammation and induce repair. Individual cytokines can be inhibited by antibodies or competitive receptors or by the therapeutic use of immunomodulatory cytokines. These biologic agents are now widely used to treat inflammatory diseases. There are a number of common renal diseases that could potentially be treated by targeting cytokines. This review will address these issues.
Cytokines are glycoproteins that regulate the functions of the immune system. Definitions are imprecise because of redundancy of function and the capacity of tissue parenchymal cells and leukocytes to produce them. Hence the terms lymphokine and monokine have been dropped. Originally described by their perceived major function, the term IL has been adopted. When an agreed characterization of a cytokine is broadly accepted, a number is attributed (e.g., IL-6). However, the use of descriptive names for some key cytokines persists, including IFNs (α, β, and γ), TNF (TNF-α and TNF-β), colony stimulating factors (granulocyte colony–stimulating factor [G-CSF] and granulocyte–macrophage colony–stimulating factor [GM-CSF]), and some growth factors (TGF-β and PDGF).
Cytokines in Host Defense
Most living organisms rely on innate immunity (in the absence of adaptive immunity) for host defense. Cytokines play critical roles in orchestrating the rapid effective response of leukocytes and parenchymal cells to the detection of microorganisms or significant noninfective damage to parenchymal cells. These cells are hardwired with receptors that recognize and respond to common pathogen proteins through Toll-like receptors (TLRs) and danger-associated molecular pattern receptors (1). Although leukocytes are the major source of innate cytokine responses, parenchymal cells are increasingly recognized as also producing innate inflammatory cytokines and interacting with leukocytes to optimize cytokine responses in generating host defense. The major acute innate cytokines, IL-1, TNF-α, IL-6, IL-12, CXCL8 (formerly IL-18), G-CSF, and GM-CSF, are used locally to activate endothelial cells and local tissue leukocytes (mast cells [MCs], dendritic cells [DCs], γδ T cells, and neurones), triggering cytokine-mediated amplification loops generating chemokine release, generating endothelial cell adhesion molecule expression, slowing blood flow, and increasing vascular permeability. These changes facilitate the accumulation of humoral defense proteins, complement, coagulation proteins, acute phase proteins, and Ig. They also recruit and activate a range of leukocytes (including innate lymphocytes, γδ T cells, natural killer cells, natural killer T cells [NKT] cells, and innate leukocyte-like cells). The net result of these orchestrated events is inflammation. Concurrently, two further processes are initiated: a cohort of cytokines (IL-1, IL-6, and TNF-α) are generated that act systemically to prepare the whole organism for microbial defense by initiating the acute response syndrome (2) and local foreign material is processed and presented by antigen-presenting cells (APCs) to initiate adaptive immunity. These secondary processes are also critically dependent on cytokine direction and are also responsive to inhibitory cytokine modulation (Figure 1).
CD4+ T cells play a central role in adaptive immunity which is characterized by antigen specificity and memory/recall capacity. T-cell specificity is a consequence of the diversity of T cell receptors (TCRs) from which thymic processing eliminates potentially autoreactive T cells to form the T-cell repertoire. Antigen recognition (signal 1) is initiated by TCR binding to antigens ingested, processed, and presented (as peptides) on major histocompatibility complex molecules by specialized APCs. Activation of T cells requires secondary signals provided by costimulatory molecules (including CD40, CD80, and CD86) expressed on APCs to engage CD154 or CD28 on T cells. Innate cytokines released at the time of antigen presentation (a third signal) determine the specific Th subset differentiation pathway the (now activated) T cells will follow. In 1986, Mossman and Coffman demonstrated that there were two separate pathways of Th subset differentiation, Th1 and Th2 (3). Th1 lineage commitment is directed by IL-12, which induces the specific signal transducers and activators of transcription (STAT) factors, STAT4 and T-bet, resulting in the production of effector cytokines, IFN-γ, and TNF-α by the differentiated Th1 cells. Th1 cells activate macrophages to mount cell-mediated immune responses against intracellular pathogens. Th2 differentiation occurs in the presence of IL-4 to activate transcription factors STAT6 and GATA3 producing IL-4, IL-5, IL-9, and IL-13 that drives humoral and IgE mediated immunity. In 2005, a new distinct Th subset was defined on the basis of its predominant production of IL-17, named Th17 cells (4). Lineage commitment of Th17 cells requires TGF-β and IL-6 for the expression of the transcription factors, STAT3 and RORγ-t, whereas maintenance and expansion of Th17 cells relies on IL-23. Activated Th17 cells produce IL-17A-F, IL-21, IL-23, and IL-22 and activate cells, particularly neutrophils, important in host defense against extracellular pathogens. Antigen presentation by TGF-β alone activates Foxp3-inducing regulatory T cells (Tregs), producing IL-10, TGF-β, and IL-35. Tregs play an important role in modulating effector T-cell responses and preventing autoimmunity.
Three further Th subsets have been defined: Th9, Th22, and T follicular helper. The Th2 subset is reprogrammed to become Th9 when IL-4 plus TGF-β activates STAT6, IRF4, GATA3, and PU.1 to produce IL-9, IL-10, IL-17, IL-21, and IL-22, promoting tissue inflammation (5). Th22 is important in skin immunity (protection and regeneration). TGF-α and IL-6 activates transcription factor, AHR, to direct the differentiation of IL-22, producing Th22 cells. T follicular helper cells migrate to follicular B-cell zones via CXCR5 where they help B cells activating Bcl-6 to produce IL-21 (6) (Table 1).
Cytokines as Therapeutic Targets
Many conventional immunomodulating drugs induce their therapeutic effects, at least in part, by attenuating the actions of injurious cytokines. These drugs include glucocorticoids. Their targets include transcription factors, nuclear factor-κ B, and activator protein 1, inducing transcription of inflammatory cytokines (7). They also effect post-translational events, including intracellular signaling and effector cytokine mRNA stability (8). Downstream effects reduce leukocyte trafficking (by attenuating TNF-α– and IL-1β–enhanced endothelial cell adhesion molecule expression). They reduce the number of circulating T cells and inhibit IL-2 production. Th cell differentiation shows a shift to Th2 with attenuation of monocyte IL-12 without effecting IL-10 production. This results in the reduction of Th1 responses favoring Th17 (9). A number of other well established anti-inflammatory drugs (pentoxifylline and thalidomide) also attenuate inflammatory cytokine gene transcription (10).
Biologic Approaches to Cytokine Therapeutic Manipulation
Attempts to biologically target cytokines were led by studies in shock; however, their beneficial effects were limited. Clinical trials in rheumatoid arthritis (RA) and psoriasis were more effective. These studies in RA and psoriasis were facilitated by the capacity to repeatedly access the affected tissues (synovial joints and skin) to determine dominant cytokines and to correlate their presence with disease severity, outcomes, and treatment responses. Administering immunoneutralizing candidate cytokines in synovial and dermal tissues in vitro allows their biologic effect to be studied. Finally, preclinical study of the biologic effects of administering or blocking cytokines in vivo in relevant animal models provided proof of concept for efficacy, specificity, and potential toxicities. The clinical success of anti–TNF-α monoclonal antibodies (mAbs) in human RA and psoriasis helped establish an accepted role for these biologics as mainstream therapeutics (11). Subsequently, anti–TNF-α strategies were successfully applied to other related rheumatologic diseases (12) and then to inflammatory bowel disease (IBD) (13). However, anti–TNF-α therapy was not effective in ANCA vasculitis (14) and multiple sclerosis (MS) (15). A number of different strategies have been used to achieve therapeutic outcomes by cytokine manipulation. Most involve neutralizing cytokine effects in disease either by immunoneutralization or the use of competitive decoy receptors (Table 2). Several potentially therapeutic mAbs targeting other key innate proinflammatory cytokines (particularly IL-1 and IL-6) were developed and tested in a number of inflammatory and autoimmune diseases.
Cytokines for Which Biologic Therapies Have Shown Clinical Effectiveness
There are now five approved therapeutics for rheumatologic use, including RA, ankylosing spondylitis, and psoriatic arthritis. Four are mAbs (infliximab, centolizumab, adalimumab, and golimumab), whereas etanercept is a recombinant human TNF receptor (Rc) fused to the Fc portion of IgG that acts as a competitive inhibitor. These therapeutics modify inflammatory joint damage and systemic inflammatory symptoms (16). Optimal outcomes in RA often require combination of conventional methotrexate with anti–TNF-α mAb (17).
IL-6 is a pleiotropic cytokine first described as a T- and B-cell growth factor produced by T cells, macrophages, and endothelial cells. It is a potent inducer of local and systemic inflammation where it plays a key role in the acute phase response (e.g., IL-6 binds to cell surface IL-6Rc and signaling is facilitated by glycoprotein 130). Tocilizumab is a mAb targeting IL-6Ra. This mAb attenuates joint inflammation, bone erosion, and systemic inflammation in RA (18). Tocilizumab is also effective in juvenile RA (Still’s disease) and Castleman’s disease (19).
IL-1 is an innate cytokine with powerful capacity to activate macrophages and epithelial cells and acts in concert with IL-6 to induce systemic acute phase responses. It has a natural antagonist, IL-1RA. IL-1RA competitively inhibits IL-1Rc binding by IL-1α and IL-1β. Anakinra is a human recombinant form of IL-1RA. Therapeutically, anakinra has been unsuccessful compared with anti–TNF-α therapy for RA, but it is highly effective in modulating the Cryopyrin-associated periodic syndromes, including neonatal onset multisystem inflammatory disease, Muckle–Wells syndrome, acute and chronic gout, and juvenile RA (20).
IL-2 is a growth factor for activated T cells. CD28-dependent costimulation of activated T cells induces expression of the high affinity IL-2 (γ, β, and δ) receptor (CD25). Basiliximab is a mAb designed to bind and block the IL-2Rc on activated T cells. This mAb is widely used to prevent early kidney transplant rejection.
A Cochrane systematic review shows that basiliximab is effective at reducing rejection 3 and 6 months postrenal transplantation. Because Tregs express high levels of CD25, there is the potential risk that its efficacy may be limited by its potential effect on blocking immunomodulation. A humanized anti–IL-2Rc mAb, daclizumab shows no apparent differences from basiliximab (21) and has been reported to be effective in treating uveitis in eight of ten patients in an open-label study (22).
These dimeric molecules share one chain in common, p40. Targeting p40 offers the opportunity to attenuate both Th1 (driven by IL-12) and Th17 (enhanced by IL-23) pathways of Th differentiation. Ustekinumab and briakinumab are such inhibitory mAbs. They have been assessed in severe refractory Crohn’s disease but without efficacy (23). Ustekinumab is also effective in psoriasis (24).
IL-17A is important in host defense by mobilizing and activating neutrophils, whereas pathologic IL-17A responses lead to the development of autoimmunity. Secukinumb is an inhibitory anti–IL-17A mAb and is effective in psoriasis, psoriatic arthritis, and ankylosing spondylitis (25); however, studies in RA show mixed results and no clear consensus of significant benefit (26). Furthermore, in Crohn’s disease treated with secukinumb, no benefit or disease excerbation was observed (27). In a phase II clinical trial, secukinumab treatment showed promising results in MS (28).
This cytokine can attenuate the production of inflammatory cytokines. IL-10 is a prominent participant in human inflammatory diseases (e.g., significant amounts can be measured in the synovium of patients with RA). Administration of IL-10 did not attenuate RA activity (29), but it is beneficial in psoriatic arthritis (30). In ulcerative colitis, IL-10 was ineffective when administered at doses that were not associated with side effects, including anemia (31).
Biologic Therapies that Have Downstream Anticytokine Effects
Cytotoxic T Lymphocyte Antigen-4
While strictly speaking, cytotoxic T lymphocyte antigen-4 (CTLA-4) Ig is not primarily a cytokine therapy, blockade of costimulatory molecules essential to adaptive immunity can secondarily block cytokine-mediated inflammation. T-cell surface receptors CD28 and CTLA-4 bind APC ligands CD80 and CD86. CD28 is pivotal in enhancing immune activation, whereas CTLA-4 delivers an inhibitory signal. Abatacept and belatecept are approved by the US Food and Drug Administration for treatment of resistant RA (32). It is effective in this situation; however, it as expected carries a risk of serious infection.
Cytokine Gene Therapy
Gene therapy has been demonstrated to be an effective way of treating pathologic inflammation. Rheumatoid synovia are arthroscopically removed from patients awaiting joint replacement and transfected with the gene for IL-1RA. Reimplantation of this transfected synovia back into the joint attenuated disease (33). This technique has also been successfully used in collagen arthritis.
Cytokine Signal Transduction Inhibition
Blocking cytokine signaling pathways can effectively prevent cytokine participation in inflammatory diseases. A number of small molecular weight inhibitors have progressed to clinical trial; however, specificity and toxicity have limited their progress to the clinic.
Janus Kinase Inhibitors
Janus kinase (JAK) inhibitors are small molecules with multiple effects on cytokine signaling pathways that inhibit the effects of cytokine-induced cell activation and consequent pathologic inflammation (34). Tofacitinib preferentially inhibits JAK-1 and JAK-3. In clinical trials, the degree of benefit in resistant RA was similar in efficacy to adalimumab, a TNF-α inhibitor. It may lack specificity because side effects, including sepsis, disturbed liver function tests, raised creatinine, and neutropenia, were reported during its use (35).
Spleen Kinase Inhibitors
Inhibition of spleen kinase signal transduction pathway prevents downstream gene transcription (i.e., synthesis of proinflammatory cytokines). The best studied spleen kinase inhibitor is fostamatinib. It has been successfully used in collagen arthritis in mice (36) and has been studied in >3000 patients with RA in several clinical trials. Responder rates for acute disease were encouraging, but side effects were common (37). Fostamatinib acts by inhibiting TNF-α–induced IL-6 production by fibroblast-like synoviocytes (38).
Collectively, data from current clinical trials are insufficient to draw general statements about cytokine therapeutic manipulation in chronic autoimmune inflammatory disease in humans. However, several observations seem appropriate. TNF-α is clearly an important mediator in injurious inflammation in several autoimmune and autoinflammatory diseases. However, there is also evidence to suggest that in other diseases, it is either redundant or potentially immunomodulatory (MS and ANCA vasculitis). IL-1β is also strongly linked to most autoinflammatory diseases and gout. Clinical trials with IL-6 are more limited, it is present together with TNF-α (in RA) and both TNF-α and IL-1β in autoinflammatory diseases. The fact that individual immunoneutralization of IL-6 is beneficial in these diseases suggests independent requirement for the expression of this cytokine. The effectiveness of IL-17 and IL-23 immunoneutralization to attenuate psoriasis and psoriatic arthritis supports the case for these diseases being Th17 mediated. However, TNF-α is also required for the generation of inflammation in this disease because TNF-α neutralization is also beneficial. Although experimental animal models have provided evidence that the CD4+ Th17 subset directs inflammatory injury in RA and IBD, the clinical data available do not support this role in human RA and IBD. However, preliminary data in MS, targeting IL-17, shows evidence of benefit. Although much more data are necessary before firm conclusions can be drawn, these observations on the therapeutic benefit on inhibiting single cytokines suggest that different combinations of cytokine may direct specific patterns of disease (Table 3).
Therapeutic Cytokine Targeting in Renal Diseases
There are three renal diseases where there is good evidence that immune cytokines play significant roles in disease pathogenesis and where their therapeutic manipulation could potentially be efficacious. These diseases are AKI, lupus nephritis, and proliferative/crescentic GN.
Innate Immunity: AKI
AKI is the most common hospital-based kidney disease (37). Much of our understanding of the mechanisms of injury in AKI come from two experimental models: ischemia reperfusion injury (IRI) and cisplatin-induced AKI. These models highlight the roles of cytokines and leukocytes in mediating injury. This is sterile inflammation. The initiating trigger is followed by tissue stress and necrosis, initiating the production of pathogen-associated molecular pattern molecules (including hypoxia-inducible factor and high-mobility group box 1), inducing the upregulation of leukocyte adhesion molecules, chemokines, and TLR signaling (39). Leukocyte infiltration is rapid and significant, involving neutrophils, monocyte, macrophages, and a variety of T cells (including CD4+ Th1 cells, natural killer cells, NKT cells, γδ T cells, and DCs) (40).
Macrophages, DCs, and MCs are potent producers of TNF-α, whereas MCs are the only leukocytes that store presynthesized TNF-α in granules. Blocking degranulation of MCs in cisplatin AKI with disodium cromoglycate prevented the increase of TNF-α in serum and protected from injury (41). Inhibition of TNF-α is also beneficial in endotoxin-, cisplatin-, and ischemia-induced AKI (42,43). IL-1 is responsible for enhancing neutrophil influx in IRI (44). NLRP3 inflammasome knockout (−/−) mice are protected against IRI but not in cisplatin-induced AKI (45). However, caspase-1−/− mice are protected from cisplatin-induced AKI (46), but IL-1β−/− mice are not (47). The role of IL-6 in AKI is complex. Evidence in ischemic AKI is consistent with an injurious role for an endogenous IL-6 (48). However in an HgCl2 model, it was shown that while IL-6–mediated inflammatory responses contributed to injury, IL-6 trans-signaling induced protective responses (49).
Cytokine-based immunomodulation can potentially be used as preventative or therapeutic in AKI. The therapeutic potential of administering anti-inflammatory cytokine IL-10 has been demonstrated to be effective in both ischemic and cisplatin-induced AKI (50). More recently, it has been appreciated that Tregs can protect from cisplatin (51) and ischemic AKI (52). Adoptive transfer of Tregs before cisplatin and before ischemia protected from the development of AKI. The number of Tregs required for protection in mice suggests the procedure is feasible in humans. Additionally, transferring Tregs to mice 24 hours after ischemic AKI was beneficial in promoting repair (53).
Cytokines released from kidneys with AKI can have significant effects on distal organs by circulatory spillover. Mortality in intensive care units is predicted by distal organ involvement in AKI. Recent studies suggest systemic proinflammatory effects are triggered in three waves by the immune release of host alarm signals (alarmins) from the AKI-damaged kidney (54). This begins with a uric acid surge, which induces a second wave of endothelial cell Weibel–Palade bodies released, which is then followed by a third wave of high-mobility group box 1 protein release. These events are potent triggers for GM-CSF, IFN-γ, CXCL8, G-CSF, IL-12, TNF-α, and IL-6 (55). Recently, renal DCs were implicated in inducing cytokine-mediated injury in ischemic AKI. Renal DCs can powerfully influence AKI by enhancing or attenuating injury. After injury, DCs initiate innate inflammatory responses presenting glycolipids and stimulating NKT cells, recruiting neutrophils and initiating the IL-17/IL-23 signaling pathway. DCs produce TNF-α, IL-6, IL-12, IL-23, IL-17, and IFN-γ to amplify injury and inflammation. However, adenosine A2ARc signaling can attenuate DC activation and protect from injury in ischemic AKI (56).
Autoimmune Crescentic Glomerulonephritis
SLE is a disease with evidence of genetic, epigenetic, and environmental contributions. There appears to be many different immune abnormalities associated with this disease, including significant abnormalities of cytokine circuits. It is also likely that there are multiple paths of autoimmunity depending in part on which component of immunomodulation is defective. Although it is likely that cytokines are therapeutic targets in this disease, the known presence of multiple immunoregulatory abnormalities suggests that SLE should not be considered as a single homogenous disease.
There is good evidence that IFN-α is an important inducer of antichromatin autoimmunity in patients developing SLE. Early in the disease, it has been demonstrated that immune complexes (containing DNA and/or RNA) are taken up by plasmacytoid DCs by FCγR-mediated internalization. Together with TLR7 and TLR9 stimulation, this induces IFN-α production, driving autoimmunity. Evidence supporting this comes from the high incidence of IFN-α–regulated genes in PBMCs of patients with SLE, the IFN-α signature (57). The levels of serum IFN-α and expression of IFN-α–regulated genes correlate with disease activity, autoantibodies, and complement levels (58). IFN-α signaling pathway polymorphisms have been shown in families with SLE (59). IFN-α is thought to be a promising therapeutic target for SLE, and several mAb inhibitors are in clinical trials. Sifalimumab is a humanized anti–IFN-α mAb. Its use in SLE was associated with reduction in SLE flares and activity (60). In a recent clinical trial, use of rontalizumab (another anti–IFN-α mAb) reduced the expression patterns of IFN-α–driven genes, improved disease severity, and improved flare rates in patients with SLE. However, patients with lupus nephritis were not included in this trial. AGS-009 is an IgG4 humanized mAb that induced significant attenuation of IFN-α signatures after a single dose (61). A novel approach has been to vaccinate patients with SLE with IFN-α–kinoid molecules to induce autoantibodies to IFN-α. All immunized patients returned the IFN-α signature to baseline (62).
Mouse models of lupus nephritis have shown both potentially protective and accentuating roles for TNF-α. New Zealand Black (NZB)/New Zealand White (NZW) and MRL/lpr mice with decreased synthetic capacity of TNF-α develop lupus nephritis, but in the kidney, intrarenal expression of TNF-α correlates with disease activity and inflammation (63). In NZB/NZW mice with IFN-α–induced nephritis, anti–TNF-α antibodies attenuate renal inflammation and injury despite maintained immune complex deposition (64).
The data on the role of TNF-α is conflicting; hence, the benefits of targeting TNF-α in human lupus nephritis is uncertain. However, there is the general view that there is sufficient data to advise against TNF-α inhibition. Several studies show that circulating levels of TNF-α and renal expression is increased (65); however, other studies show TNF-α production by PBMCs was lower in patients with lupus nephritis than controls (66). Additionally, TNF-α production was associated with reduced TNF-α bioactivity because of high serum levels of TNF receptors, which also correlated with increased disease activity (67). Finally, in patients with lupus nephritis, 10 weeks of infliximab treatment reduced proteinuria but increased anti-DNA antibodies. Longer treatment was associated with adverse effects (68). In patients with RA treated with anti–TNF-α mAbs, lupus syndromes developed, anti-DNAs were induced (69), and some patients developed GN (70).
IL-6 is likely to act in concert with type 1 IFNs to induce B-cell autoimmunity in SLE. Its levels are elevated in lupus nephritis and correlate with disease activity (71). IL-6 has been demonstrated in glomerular immune complexes and proximal tubular epithelial cells in lupus nephritis (72). Intrinsic renal cells produce IL-6, and this can be enhanced by anti-DNA antibodies (73). In lupus-prone mice, IL-6 exacerbates GN while inhibiting IL-6 signaling attenuated GN and reducing autoimmunity, therefore enhancing survival (74). Most IL-6 inhibition trials have occurred in RA while data are emerging in SLE. Tocilizumab reduced acute phase reactants, anti–double-stranded DNA antibody, and SELENA-SLEDAI scores in patients with moderately active lupus nephritis (75).
A number of biologic interventions target molecules or immune cells upstream of cytokine production. The beneficial effects are likely to result from their effects on cytokine mediation of target organ inflammation.
B-cell Activating Factor.
B-cell activating factor is also known as B lymphocyte stimulator and is essential for B-cell maturation, survival, and Ig class switching. Its levels are elevated in SLE and correlate with disease activity and flares (76). Belimumab, a humanized anti-B lymphocyte stimulator mAb has been shown in two trials to demonstrate a modest but significant benefit in reducing disease activity. Patients with lupus nephritis were excluded, but in one trial, 15% of patients had evidence of nephritis. A post hoc analysis showed significant reduction in proteinuria. Trials in lupus nephritis are underway (77,78).
The data at hand do not provide evidence for CTLA4-Ig efficacy in the treatment of lupus nephritis. A phase IIb trial involving patients with lupus with polyarthritis and discoid lupus did not meet its primary or secondary end point, flare prevention, and the infection incidence was significantly higher in the abatacept arm (79). In another 12-month trial of abatacept or placebo, intravenous infusion plus steroid and mycophenolate mofetil were compared in patients with class III and class IV lupus nephritis. Complete response and renal improvement criteria were the same in all groups. Infection was not higher in the abatacept group (80).
Anti–TNF-Related Weak Inducer of Apoptosis.
There is growing evidence for the anti–TNF-related weak inducer of apoptosis (Tweak)/factor inducible 14 pathway in enhancing injury in lupus nephritis. In lupus nephritis, Tweak and its receptor are upregulated in renal tubular cells, inducing proinflammatory cytokines, including IL-6, adhesion molecules, and chemokines (81). Immunoneutralization of Tweak decreases renal inflammation in murine models (82), and these mAb are being studied in lupus nephritis (ClinicalTrials.gov identifier: NCT0130890).
Laquinimod is a small molecule that immunomodulates APCs to redirect Th subset differentiation with downregulation of IL-6, IL-12, IL-23, IL-17, and TNF-α and increased IL-10. In experimental murine lupus, laquinimod delayed the onset of lupus nephritis. When administered as a therapeutic, it attenuated disease severity by reducing IFN-γ and IL-17A production by splenocytes while enhancing IL-10 and Treg frequency (83). In a phase II study in active lupus nephritis, mycophenolate mofetil and high-dose steroid were administered with or without laquinimod. Laquinimod had an additive effect with renal function and proteinuria improvement. Adverse effects were not observed (84).
Despite many trials of therapeutics that attenuate cytokine action being performed in SLE, there is still much that needs to be understood about the role of cytokines in this disease. Unfortunately, the simple application of therapies successful in other immune inflammatory diseases (as in the case of anti–TNF-α immune neutralization) appears to be much more problematic in SLE. Finally, the diversity of patterns of disease and the involvement of different organs means lupus nephritis is unfortunately an exclusion in many trials, denying these patients the opportunity for potentially more effective treatments.
Experimental Antiglomerular Basement Membrane Glomerulonephritis.
Experimental antiglomerular basement membrane (GBM) GN is the most widely studied animal model of human crescentic GN. There is considerable data showing that immune cytokines are critically involved in inducing nephritogenic autoimmunity and mediating glomerular injury in these models. Moreover, studies in this model provide proof of concept that the inhibition of selected cytokines can prevent and treat disease.
Numerous innate cytokines have been associated with pathogenesis of anti-GBM GN. A pathogenic role in anti-GBM GN has been demonstrated for each of the following innate cytokines: GM-CSF, G-CSF, IL-1β, TNF-α, and CXCL8, by studies in cytokine gene–deleted mice. All of these innate cytokines recruit inflammatory cells to the kidney and direct the subsequent development of anti-GBM GN. Gene deletion of the key Th1 cytokines (IL-12 and IFN-γ) resulted in attenuated crescentic GN, and gene deletion of the key Th1 transcription factor (T-bet) is protective (85,86). After the discovery of the CD4+ Th17 subset, studies using mice deficient in p19, p35, and p40 (components of the key Th1 and Th17 cytokines, IL-12 and IL-23, respectively) were used to analyze the relative contributions of each Th subset in anti-GBM GN. Paust et al. demonstrated that Th17 cells contributes to anti-GBM GN with the use of IL-23p19−/− and IL-17A−/− mice (87), whereas Odobasic et al. examined the reciprocal relationship between Th1 and Th17 and demonstrated that early nephritogenic responses were mediated by Th17 cells, but late disease is Th1 dependent. They also demonstrated that each Th subset counter-regulated the other (88). Furthermore, Steinmetz et al. used mice with gene deletion of RORγ-t, the key Th17 transcription factor, to confirm the participation of the CD4+ Th17 subset (89). Direct comparison has been made between the effects of transferring Th17 and Th1 polarized ovalbumin (OVA) specific CD4+ TCR transgenic cells into naïve mice with OVA planted on the GBM using a non-nephritogenic anti-GBM/OVA conjugated antibody. Transfer of both CD4+ T-cell clones induced GN. However, transfer of Th1-polarized cells induced a monocyte and macrophage predominant infiltrate lesion, whereas Th17-polarized cells induced less injury with a neutrophil predominant infiltrate (90). To assess key Th2 cytokines, anti-GBM GN was induced in IL-4−/− and IL-10−/− mice. Both groups had augmented Th1 responses and increased glomerular injury, whereas infusion of IL-10 attenuated disease. Tregs are not only important in maintaining self-tolerance but are also necessary in controlling overt inflammatory responses. Transfer of Tregs (CD4+CD25+) before and after the induction of experimental anti-GBM GN suppressed the development of GN by reducing Th1 responses (91). Interestingly, Eller et al. demonstrated that Treg-derived IL-9 is essential for the recruitment of MCs, and both are required to attenuate anti-GBM GN (92).
Cytokine Production by Resident Renal Cells.
Resident cells within the kidney, including tubular and glomerular cells, interact with infiltrating leukocytes resulting in their synthesis of injurious TNF-α in response to leukocyte-produced IL-1 (73). The relative roles of leukocyte and resident cytokine production have been studied in anti-GBM GN in mice using cytokine chimeric mice where the cytokine gene has been deleted from either bone marrow–derived leukocytes or from resident renal cells (86). Nonchimeric TNF-α−/− mice are significantly protected from the development of GN. When the TNF-α gene is knocked out from resident cells, similar attenuation was observed, whereas knockout of the TNF-α gene in bone marrow only caused mild protection, suggesting that TNF-α produced by resident cells is the major source of injurious TNF-α in this disease. These studies also produced evidence of complex cytokine interactions between resident cells and infiltrating leukocytes. Studies with IL-1β−/− and IL-1R1−/− mice showed that IL-1β mainly derived from leukocytes actives IL-1R1 on resident cells, inducing TNF-α production that causes significant glomerular injury (86) (Figure 2).
Autoimmune Anti-GBM Glomerulonephritis.
In autoimmune anti-GBM GN, the target autoantigen is the noncollagenase domain of the alpha 3 chain of type IV collagen. Immunization with this antigen induces autoimmunity shown by the production of circulating anti-GBM antibodies and the development of crescentic GN. IFN-γ−/− mice developed worse disease. The relative contributions of Th1 and Th17 to disease development were assessed using p35−/− (deficient in Th1 subset) and p19−/− (deficient in Th17 subset) mice. The p19−/− mice were protected from GN, but the p35−/− mice were unaffected compared with controls, confirming a pathogenic role for Th17 but not for Th1 in this disease.
ANCA-Associated Crescentic Glomerulonephritis.
The most common cause of crescentic GN is ANCA-associated vasculitis (AAV). Evidence suggests cytokines directing the underlying nephritogenic autoimmunity are likely to be therapeutic targets that could be neutralized with available biologic agents.
PBMCs from patients with ANCA-associated GN have CD4+ T cells that proliferate when stimulated with the target autoantigens, proteinase 3 or myeloperoxidase (MPO) (93). In treatment of refractory disease with T cell–specific targeted therapies, antithymocyte globulin was beneficial and capable of inducing remission (94). Furthermore, cytokine profiling of biopsied nasal mucosal tissue, bronchoalveolar lavage, and PBMCs from patients with granulomatous polyangiitis demonstrated increased expression of IFN-γ, denoting a Th1 cytokine pattern (95). Nogueira et al. found that in the serum of acute or convalescent AAV patients, IL-17A and IL-23 levels were increased, and this correlated with disease severity and ANCA titer (96). IL-6 was also elevated in active disease. Chavele et al. reported that in patients with MPO-AAV, MPO-stimulated recall responses showed elevated IFN-γ (97). Collectively, these data provide evidence in support of both Th1 and Th17 involvement in AAV. Furthermore, IL-17–producing cells were found in renal biopsies from patients with acute vasculitis, and most of the IL-17–positive cells present were innate leukocytes (neutrophils and MCs) (98).
In experimental MPO-ANCA GN, IL-17A−/− mice were protected from the development of anti-MPO autoimmunity and glomerular injury (99). Immunoneutralization of TNF-α caused significant reduction in lung hemorrhage and renal injury in Wistar–Kyoto rats with induced anti-MPO AAV (100).
The only cytokine-based clinical trials in AAV have been of anti–TNF-α. Treatment with etanercept (anti–TNF-α mAb) was not effective and was associated with a high rate of treatment-related adverse side effects (101). A smaller clinical trial using adalimumab with prednisolone plus cyclophosphamide showed similar efficacy to using these drugs but afforded with less steroid exposure (102).
Opportunities for Introducing Biologic Therapies to Treat Renal Diseases
The evidence outlined here suggests that there are important renal diseases that may benefit from the application of well targeted biologic therapies on the basis of cytokine manipulation.
Innate cytokines are prominent participants in many forms of AKI. Moreover, in some clinical settings, such as renal transplantation, high-risk surgery (e.g., elective coronary grafting), and for optimal use of effective chemotherapeutics (nephrotoxic dose-limited like cisplatin), the opportunity exists to preemptively block likely injurious cytokine pathways.There is a need for more selective, less toxic therapies to treat autoimmune inflammatory forms of proliferative/crescentic GN, including lupus nephritis, anti-GBM, and ANCA-associated disease. These represent the more serious and inflammatory categories of theses autoimmune diseases. They share features of other diseases, such as RA and IBD, where new biologics are now part of the therapeutic pharmacopeia.
The initial attempt to introduce anti–TNF-α mAbs in AAV was disappointing. It should remind us that translation of therapies from one disease to another is not simple or without risk, but without well managed risk, there will be no progress. Perhaps we should apply the principles behind the introduction of anti–TNF-α to RA, use tissue samples from patients with active disease to assess the dominant cytokines in active untreated disease, assess the effects of these cytokines on relevant renal tissues in vitro, and use relevant animal models to provide proof of concept for the specificity, efficacy, and minimal toxicity in preclinical trials. Clinical trials with the greatest likelihood of success are those that target dominant cytokines in renal diseases using immunoneutralising mAbs where minimal toxicity and clinical effectiveness has already been shown in other chronic autoimmune and or autoinflammatory disease. Using these criteria we could now be planning clinical trials for targeting the major innate cytokine as prophylaxis and treatment and considering neutralizing mAbs to IL-17 and IL-23 in ANCA vasculitis.
Published online ahead of print. Publication date available at www.cjasn.org.
1. Eleftheriadis T, Pissas G, Liakopoulos V, Stefanidis I, Lawson BR: Toll-like receptors and their role in renal pathologies. Inflamm Allergy Drug Targets 11: 464–477, 2012
2. Gabay C, Kushner I: Acute-phase proteins and other systemic responses to inflammation. N Engl J Med 340: 448–454, 1999
3. Mosmann TR, Cherwinski H, Bond MW, Giedlin MA, Coffman RL: Two types of murine helper T cell clone. I. Definition according to profiles of lymphokine activities and secreted proteins. J Immunol 136: 2348–2357, 1986
4. Langrish CL, Chen Y, Blumenschein WM, Mattson J, Basham B, Sedgwick JD, McClanahan T, Kastelein RA, Cua DJ: IL-23 drives a pathogenic T cell population that induces autoimmune inflammation. J Exp Med 201: 233–240, 2005
5. Kaplan MH: Th9 cells: Differentiation and disease. Immunol Rev 252: 104–115, 2013
6. Crotty S: Follicular helper CD4 T cells (TFH). Annu Rev Immunol 29: 621–663, 2011
7. Auphan N, DiDonato JA, Rosette C, Helmberg A, Karin M: Immunosuppression by glucocorticoids: Inhibition of NF-kappa B activity through induction of I kappa B synthesis. Science 270: 286–290, 1995
8. Göttlicher M, Heck S, Herrlich P: Transcriptional cross-talk, the second mode of steroid hormone receptor action. J Mol Med (Berl) 76: 480–489, 1998
9. Weaver CT, Harrington LE, Mangan PR, Gavrieli M, Murphy KM: Th17: An effector CD4 T cell lineage with regulatory T cell ties. Immunity 24: 677–688, 2006
10. Kiely PD, Johnson D, Bourke BE: An open study of oxpentifylline in early rheumatoid arthritis. Br J Rheumatol 37: 1033–1035, 1998
11. Elliott MJ, Maini RN, Feldmann M, Kalden JR, Antoni C, Smolen JS, Leeb B, Breedveld FC, Macfarlane JD, Bijl H: Randomised double-blind comparison of chimeric monoclonal antibody to tumour necrosis factor alpha (cA2) versus placebo in rheumatoid arthritis. Lancet 344: 1105–1110, 1994
12. Braun J, Brandt J, Listing J, Zink A, Alten R, Golder W, Gromnica-Ihle E, Kellner H, Krause A, Schneider M, Sörensen H, Zeidler H, Thriene W, Sieper J: Treatment of active ankylosing spondylitis with infliximab: A randomised controlled multicentre trial. Lancet 359: 1187–1193, 2002
13. Rutgeerts P, Sandborn WJ, Feagan BG, Reinisch W, Olson A, Johanns J, Travers S, Rachmilewitz D, Hanauer SB, Lichtenstein GR, de Villiers WJ, Present D, Sands BE, Colombel JF: Infliximab for induction and maintenance therapy for ulcerative colitis. N Engl J Med 353: 2462–2476, 2005
14. Stone JH, Holbrook JT, Marriott MA, Tibbs AK, Sejismundo LP, Min YI, Specks U, Merkel PA, Spiera R, Davis JC, St Clair EW, McCune WJ, Ytterberg SR, Allen NB, Hoffman GS; Wegener’s Granulomatosis Etanercept Trial Research Group: Solid malignancies among patients in the Wegener’s Granulomatosis Etanercept Trial. Arthritis Rheum 54: 1608–1618, 2006
15. The Lenercept Multiple Sclerosis Study Group and The University of British Columbia MS/MRI Analysis Group: TNF neutralization in MS: Results of a randomized, placebo-controlled multicenter study. Neurology 53: 457–465, 1999
16. Probert L, Eugster HP, Akassoglou K, Bauer J, Frei K, Lassmann H, Fontana A: TNFR1 signalling is critical for the development of demyelination and the limitation of T-cell responses during immune-mediated CNS disease. Brain 123: 2005–2019, 2000
17. Feldmann M, Maini RN: Anti-TNF therapy, from rationale to standard of care: What lessons has it taught us? J Immunol 185: 791–794, 2010
18. Smolen JS, Beaulieu A, Rubbert-Roth A, Ramos-Remus C, Rovensky J, Alecock E, Woodworth T, Alten R; OPTION Investigators: Effect of interleukin-6 receptor inhibition with tocilizumab in patients with rheumatoid arthritis (OPTION study): A double-blind, placebo-controlled, randomised trial. Lancet 371: 987–997, 2008
19. De Benedetti F, Brunner HI, Ruperto N, Kenwright A, Wright S, Calvo I, Cuttica R, Ravelli A, Schneider R, Woo P, Wouters C, Xavier R, Zemel L, Baildam E, Burgos-Vargas R, Dolezalova P, Garay SM, Merino R, Joos R, Grom A, Wulffraat N, Zuber Z, Zulian F, Lovell D, Martini A; PRINTO; PRCSG: Randomized trial of tocilizumab in systemic juvenile idiopathic arthritis. N Engl J Med 367: 2385–2395, 2012
20. Dinarello CA, Simon A, van der Meer JW: Treating inflammation by blocking interleukin-1 in a broad spectrum of diseases. Nat Rev Drug Discov 11: 633–652, 2012
21. Webster AC, Ruster LP, McGee R, Matheson SL, Higgins GY, Willis NS, Chapman JR, Craig JC: Interleukin 2 receptor antagonists for kidney transplant recipients. Cochrane Database Syst Rev (1): CD003897, 2010
22. Nussenblatt RB, Fortin E, Schiffman R, Rizzo L, Smith J, Van Veldhuisen P, Sran P, Yaffe A, Goldman CK, Waldmann TA, Whitcup SM: Treatment of noninfectious intermediate and posterior uveitis with the humanized anti-Tac mAb: A phase I/II clinical trial
. Proc Natl Acad Sci U S A 96: 7462–7466, 1999
23. Sandborn WJ, Feagan BG, Fedorak RN, Scherl E, Fleisher MR, Katz S, Johanns J, Blank M, Rutgeerts P; Ustekinumab Crohn’s Disease Study Group: A randomized trial of Ustekinumab, a human interleukin-12/23 monoclonal antibody, in patients with moderate-to-severe Crohn’s disease. Gastroenterology 135: 1130–1141, 2008
24. McInnes IB, Kavanaugh A, Gottlieb AB, Puig L, Rahman P, Ritchlin C, Brodmerkel C, Li S, Wang Y, Mendelsohn AM, Doyle MK; PSUMMIT 1 Study Group: Efficacy and safety of ustekinumab in patients with active psoriatic arthritis: 1 year results of the phase 3, multicentre, double-blind, placebo-controlled PSUMMIT 1 trial. Lancet 382: 780–789, 2013
25. Leonardi C, Matheson R, Zachariae C, Cameron G, Li L, Edson-Heredia E, Braun D, Banerjee S: Anti-interleukin-17 monoclonal antibody ixekizumab in chronic plaque psoriasis. N Engl J Med 366: 1190–1199, 2012
26. Genovese MC, Durez P, Richards HB, Supronik J, Dokoupilova E, Mazurov V, Aelion JA, Lee SH, Codding CE, Kellner H, Ikawa T, Hugot S, Mpofu S: Efficacy and safety of secukinumab in patients with rheumatoid arthritis: A phase II, dose-finding, double-blind, randomised, placebo controlled study. Ann Rheum Dis 72: 863–869, 2013
27. Hueber W, Sands BE, Lewitzky S, Vandemeulebroecke M, Reinisch W, Higgins PD, Wehkamp J, Feagan BG, Yao MD, Karczewski M, Karczewski J, Pezous N, Bek S, Bruin G, Mellgard B, Berger C, Londei M, Bertolino AP, Tougas G, Travis SP; Secukinumab in Crohn’s Disease Study Group: Secukinumab, a human anti-IL-17A monoclonal antibody, for moderate to severe Crohn’s disease: Unexpected results of a randomised, double-blind placebo-controlled trial. Gut 61: 1693–1700, 2012
28. A Phase II, Multicenter, Randomized, Double-Blind, Parallel Group, Placebo-Controlled, Adaptive Dose-Ranging Study to Evaluate the Efficacy and Safety of AIN457 (Secukinumab) in Patients with Relapsing Multiple Sclerosis. Available at: https://clinicaltrials.gov/show/NCT01874340
. Accessed August 1, 2014
29. Maini RN, Paulus H, Breedveld FC, Moreland LW, William E, Russell AS, Charles P, Davies D, Grint P, Wherry JC, Feldmann M: rHuIL-10 in subjects with active rheumatoid arthritis (RA): A phase I and cytokine response study. Arthritis Rheum 40: S224, 1997
30. McInnes IB, Illei GG, Danning CL, Yarboro CH, Crane M, Kuroiwa T, Schlimgen R, Lee E, Foster B, Flemming D, Prussin C, Fleisher TA, Boumpas DT: IL-10 improves skin disease and modulates endothelial activation and leukocyte effector function in patients with psoriatic arthritis. J Immunol 167: 4075–4082, 2001
31. Fedorak RN, Gangl A, Elson CO, Rutgeerts P, Schreiber S, Wild G, Hanauer SB, Kilian A, Cohard M, LeBeaut A, Feagan B: Recombinant human interleukin 10 in the treatment of patients with mild to moderately active Crohn’s disease. The Interleukin 10 Inflammatory Bowel Disease Cooperative Study Group. Gastroenterology 119: 1473–1482, 2000
32. Maxwell LJ, Singh JA: Abatacept for rheumatoid arthritis: A Cochrane systematic review. J Rheumatol 37: 234–245, 2010
33. Evans CH, Robbins PD, Ghivizzani SC, Wasko MC, Tomaino MM, Kang R, Muzzonigro TA, Vogt M, Elder EM, Whiteside TL, Watkins SC, Herndon JH: Gene transfer to human joints: Progress toward a gene therapy of arthritis. Proc Natl Acad Sci U S A 102: 8698–8703, 2005
34. Sengupta TK, Schmitt EM, Ivashkiv LB: Inhibition of cytokines
and JAK-STAT activation by distinct signaling pathways. Proc Natl Acad Sci U S A 93: 9499–9504, 1996
35. van Vollenhoven RF, Fleischmann R, Cohen S, Lee EB, García Meijide JA, Wagner S, Forejtova S, Zwillich SH, Gruben D, Koncz T, Wallenstein GV, Krishnaswami S, Bradley JD, Wilkinson B; ORAL Standard Investigators: Tofacitinib or adalimumab versus placebo in rheumatoid arthritis. N Engl J Med 367: 508–519, 2012
36. Pine PR, Chang B, Schoettler N, Banquerigo ML, Wang S, Lau A, Zhao F, Grossbard EB, Payan DG, Brahn E: Inflammation and bone erosion are suppressed in models of rheumatoid arthritis following treatment with a novel Syk inhibitor. Clin Immunol 124: 244–257, 2007
37. Weinblatt ME, Kavanaugh A, Genovese MC, Musser TK, Grossbard EB, Magilavy DB: An oral spleen tyrosine kinase (Syk) inhibitor for rheumatoid arthritis. N Engl J Med 363: 1303–1312, 2010
38. Mun SH, Kim JW, Nah SS, Ko NY, Lee JH, Kim JD, Kim K, Kim HS, Choi JD, Kim SH, Lee CK, Park SH, Kim BK, Kim HS, Kim YM, Choi WS: Tumor necrosis factor alpha-induced interleukin-32 is positively regulated via the Syk/protein kinase Cdelta/JNK pathway in rheumatoid synovial fibroblasts. Arthritis Rheum 60: 678–685, 2009
39. Vallés PG, Lorenzo AG, Bocanegra V, Vallés R: Acute kidney injury: what part do toll-like receptors play? Int J Nephrol Renovasc Dis 7: 241–251, 2014
40. Kinsey GR, Okusa MD: Role of leukocytes in the pathogenesis of acute kidney injury. Crit Care 16: 214, 2012
41. Summers SA, Chan J, Gan PY, Dewage L, Nozaki Y, Steinmetz OM, Nikolic-Paterson DJ, Kitching AR, Holdsworth SR: Mast cells mediate acute kidney injury through the production of TNF. J Am Soc Nephrol 22: 2226–2236, 2011
42. Donnahoo KK, Meng X, Ayala A, Cain MP, Harken AH, Meldrum DR: Early kidney TNF-alpha expression mediates neutrophil infiltration and injury after renal ischemia-reperfusion. Am J Physiol 277: R922–R929, 1999
43. Akcay A, Nguyen Q, Edelstein CL: Mediators of inflammation in acute kidney injury. Mediators Inflamm 2009: 137072, 2009
44. Burne MJ, Elghandour A, Haq M, Saba SR, Norman J, Condon T, Bennett F, Rabb H: IL-1 and TNF independent pathways mediate ICAM-1/VCAM-1 up-regulation in ischemia reperfusion injury. J Leukoc Biol 70: 192–198, 2001
45. Kim HJ, Lee DW, Ravichandran K, O Keys D, Akcay A, Nguyen Q, He Z, Jani A, Ljubanovic D, Edelstein CL: NLRP3 inflammasome knockout mice are protected against ischemic but not cisplatin-induced acute kidney injury. J Pharmacol Exp Ther 346: 465–472, 2013
46. Faubel S, Ljubanovic D, Reznikov L, Somerset H, Dinarello CA, Edelstein CL: Caspase-1-deficient mice are protected against cisplatin-induced apoptosis and acute tubular necrosis. Kidney Int 66: 2202–2213, 2004
47. Faubel S, Lewis EC, Reznikov L, Ljubanovic D, Hoke TS, Somerset H, Oh DJ, Lu L, Klein CL, Dinarello CA, Edelstein CL: Cisplatin-induced acute renal failure is associated with an increase in the cytokines
interleukin (IL)-1beta, IL-18, IL-6, and neutrophil infiltration in the kidney. J Pharmacol Exp Ther 322: 8–15, 2007
48. Patel NS, Chatterjee PK, Di Paola R, Mazzon E, Britti D, De Sarro A, Cuzzocrea S, Thiemermann C: Endogenous interleukin-6 enhances the renal injury, dysfunction, and inflammation caused by ischemia/reperfusion. J Pharmacol Exp Ther 312: 1170–1178, 2005
49. Nechemia-Arbely Y, Barkan D, Pizov G, Shriki A, Rose-John S, Galun E, Axelrod JH: IL-6/IL-6R axis plays a critical role in acute kidney injury. J Am Soc Nephrol 19: 1106–1115, 2008
50. Deng J, Kohda Y, Chiao H, Wang Y, Hu X, Hewitt SM, Miyaji T, McLeroy P, Nibhanupudy B, Li S, Star RA: Interleukin-10 inhibits ischemic and cisplatin-induced acute renal injury. Kidney Int 60: 2118–2128, 2001
51. Lee H, Nho D, Chung HS, Lee H, Shin MK, Kim SH, Bae H: CD4+CD25+ regulatory T cells attenuate cisplatin-induced nephrotoxicity in mice. Kidney Int 78: 1100–1109, 2010
52. Kinsey GR, Sharma R, Huang L, Li L, Vergis AL, Ye H, Ju ST, Okusa MD: Regulatory T cells suppress innate immunity in kidney ischemia-reperfusion injury. J Am Soc Nephrol 20: 1744–1753, 2009
53. Gandolfo MT, Jang HR, Bagnasco SM, Ko GJ, Agreda P, Satpute SR, Crow MT, King LS, Rabb H: Foxp3+ regulatory T cells participate in repair of ischemic acute kidney injury. Kidney Int 76: 717–729, 2009
54. Ratliff BB, Rabadi MM, Vasko R, Yasuda K, Goligorsky MS: Messengers without borders: Mediators of systemic inflammatory response in AKI. J Am Soc Nephrol 24: 529–536, 2013
55. Wang H, Bloom O, Zhang M, Vishnubhakat JM, Ombrellino M, Che J, Frazier A, Yang H, Ivanova S, Borovikova L, Manogue KR, Faist E, Abraham E, Andersson J, Andersson U, Molina PE, Abumrad NN, Sama A, Tracey KJ: HMG-1 as a late mediator of endotoxin lethality in mice. Science 285: 248–251, 1999
56. Okusa MD, Li L: Dendritic cells in acute kidney injury: cues from the microenvironment. Trans Am Clin Climatol Assoc 123: 54–62, discussion 62–63, 2012
57. Rönnblom L, Eloranta ML, Alm GV: The type I interferon system in systemic lupus erythematosus. Arthritis Rheum 54: 408–420, 2006
58. Feng X, Wu H, Grossman JM, Hanvivadhanakul P, FitzGerald JD, Park GS, Dong X, Chen W, Kim MH, Weng HH, Furst DE, Gorn A, McMahon M, Taylor M, Brahn E, Hahn BH, Tsao BP: Association of increased interferon-inducible gene expression with disease activity and lupus nephritis in patients with systemic lupus erythematosus. Arthritis Rheum 54: 2951–2962, 2006
59. Criswell LA: The genetic contribution to systemic lupus erythematosus. Bull NYU Hosp Jt Dis 66: 176–183, 2008
60. Petri M, Wallace DJ, Spindler A, Chindalore V, Kalunian K, Mysler E, Neuwelt CM, Robbie G, White WI, Higgs BW, Yao Y, Wang L, Ethgen D, Greth W: Sifalimumab, a human anti-interferon-α monoclonal antibody, in systemic lupus erythematosus: A phase I randomized, controlled, dose-escalation study. Arthritis Rheum 65: 1011–1021, 2013
61. Tcherepanova I, Curtis M, Sale M, Miesowicz F, Nicolette C: Results of a randomized placebo controlled phase IA study of AGS-009, a humanized anti-interferon-alpha monoclonal antibody in subjects with systemic lupus erythematosus. Ann Rheum Dis 71[Suppl 3]: 536–537, 2013
62. Lauwerys BR, Hachulla E, Spertini F, Lazaro E, Jorgensen C, Mariette X, Haelterman E, Grouard-Vogel G, Fanget B, Dhellin O, Vandepapelière P, Houssiau FA: Down-regulation of interferon signature in systemic lupus erythematosus patients by active immunization with interferon α-kinoid. Arthritis Rheum 65: 447–456, 2013
63. Brennan DC, Yui MA, Wuthrich RP, Kelley VE: Tumor necrosis factor and IL-1 in New Zealand Black/White mice. Enhanced gene expression and acceleration of renal injury. J Immunol 143: 3470–3475, 1989
64. Bethunaickan R, Sahu R, Liu Z, Tang YT, Huang W, Edegbe O, Tao H, Ramanujam M, Madaio MP, Davidson A: Anti-tumor necrosis factor α treatment of interferon-α-induced murine lupus nephritis reduces the renal macrophage response but does not alter glomerular immune complex formation. Arthritis Rheum 64: 3399–3408, 2012
65. Gigante A, Gasperini ML, Afeltra A, Barbano B, Margiotta D, Cianci R, De Francesco I, Amoroso A: Cytokines
expression in SLE nephritis. Eur Rev Med Pharmacol Sci 15: 15–24, 2011
66. Yu CL, Chang KL, Chiu CC, Chiang BN, Han SH, Wang SR: Defective phagocytosis, decreased tumour necrosis factor-alpha production, and lymphocyte hyporesponsiveness predispose patients with systemic lupus erythematosus to infections. Scand J Rheumatol 18: 97–105, 1989
67. Aderka D, Wysenbeek A, Engelmann H, Cope AP, Brennan F, Molad Y, Hornik V, Levo Y, Maini RN, Feldmann M, Wallach D: Correlation between serum levels of soluble tumor necrosis factor receptor and disease activity in systemic lupus erythematosus. Arthritis Rheum 36: 1111–1120, 1993
68. Aringer M, Houssiau F, Gordon C, Graninger WB, Voll RE, Rath E, Steiner G, Smolen JS: Adverse events and efficacy of TNF-alpha blockade with infliximab in patients with systemic lupus erythematosus: Long-term follow-up of 13 patients. Rheumatology (Oxford) 48: 1451–1454, 2009
69. Charles PJ, Smeenk RJ, De Jong J, Feldmann M, Maini RN: Assessment of antibodies to double-stranded DNA induced in rheumatoid arthritis patients following treatment with infliximab, a monoclonal antibody to tumor necrosis factor alpha: Findings in open-label and randomized placebo-controlled trials. Arthritis Rheum 43: 2383–2390, 2000
70. Stokes MB, Foster K, Markowitz GS, Ebrahimi F, Hines W, Kaufman D, Moore B, Wolde D, D’Agati VD: Development of glomerulonephritis during anti-TNF-alpha therapy for rheumatoid arthritis. Nephrol Dial Transplant 20: 1400–1406, 2005
71. Chun HY, Chung JW, Kim HA, Yun JM, Jeon JY, Ye YM, Kim SH, Park HS, Suh CH: Cytokine IL-6 and IL-10 as biomarkers in systemic lupus erythematosus. J Clin Immunol 27: 461–466, 2007
72. Malide D, Russo P, Bendayan M: Presence of tumor necrosis factor alpha and interleukin-6 in renal mesangial cells of lupus nephritis patients. Hum Pathol 26: 558–564, 1995
73. Yung S, Cheung KF, Zhang Q, Chan TM: Mediators of inflammation and their effect on resident renal cells: implications in lupus nephritis. Clin Dev Immunol 2013: 317682, 2013
74. Cash H, Relle M, Menke J, Brochhausen C, Jones SA, Topley N, Galle PR, Schwarting A: Interleukin 6 (IL-6) deficiency delays lupus nephritis in MRL-Faslpr mice: The IL-6 pathway as a new therapeutic target in treatment of autoimmune kidney disease in systemic lupus erythematosus. J Rheumatol 37: 60–70, 2010
75. Illei GG, Shirota Y, Yarboro CH, Daruwalla J, Tackey E, Takada K, Fleisher T, Balow JE, Lipsky PE: Tocilizumab in systemic lupus erythematosus: Data on safety, preliminary efficacy, and impact on circulating plasma cells from an open-label phase I dosage-escalation study. Arthritis Rheum 62: 542–552, 2010
76. Petri M, Stohl W, Chatham W, McCune WJ, Chevrier M, Ryel J, Recta V, Zhong J, Freimuth W: Association of plasma B lymphocyte stimulator levels and disease activity in systemic lupus erythematosus. Arthritis Rheum 58: 2453–2459, 2008
77. Navarra SV, Guzmán RM, Gallacher AE, Hall S, Levy RA, Jimenez RE, Li EK, Thomas M, Kim HY, León MG, Tanasescu C, Nasonov E, Lan JL, Pineda L, Zhong ZJ, Freimuth W, Petri MA; BLISS-52 Study Group: Efficacy and safety of belimumab in patients with active systemic lupus erythematosus: A randomised, placebo-controlled, phase 3 trial. Lancet 377: 721–731, 2011
78. Furie R, Petri M, Zamani O, Cervera R, Wallace DJ, Tegzová D, Sanchez-Guerrero J, Schwarting A, Merrill JT, Chatham WW, Stohl W, Ginzler EM, Hough DR, Zhong ZJ, Freimuth W, van Vollenhoven RF; BLISS-76 Study Group: A phase III, randomized, placebo-controlled study of belimumab, a monoclonal antibody that inhibits B lymphocyte stimulator, in patients with systemic lupus erythematosus. Arthritis Rheum 63: 3918–3930, 2011
79. Merrill JT, Burgos-Vargas R, Westhovens R, Chalmers A, D’Cruz D, Wallace DJ, Bae SC, Sigal L, Becker JC, Kelly S, Raghupathi K, Li T, Peng Y, Kinaszczuk M, Nash P: The efficacy and safety of abatacept in patients with non-life-threatening manifestations of systemic lupus erythematosus: Results of a twelve-month, multicenter, exploratory, phase IIb, randomized, double-blind, placebo-controlled trial. Arthritis Rheum 62: 3077–3087, 2010
80. Wofsy D, Hillson JL, Diamond B: Abatacept for lupus nephritis: Alternative definitions of complete response support conflicting conclusions. Arthritis Rheum 64: 3660–3665, 2012
81. Sanz AB, Justo P, Sanchez-Niño MD, Blanco-Colio LM, Winkles JA, Kreztler M, Jakubowski A, Blanco J, Egido J, Ruiz-Ortega M, Ortiz A: The cytokine TWEAK modulates renal tubulointerstitial inflammation. J Am Soc Nephrol 19: 695–703, 2008
82. Xia Y, Campbell SR, Broder A, Herlitz L, Abadi M, Wu P, Michaelson JS, Burkly LC, Putterman C: Inhibition of the TWEAK/Fn14 pathway attenuates renal disease in nephrotoxic serum nephritis. Clin Immunol 145: 108–121, 2012
83. Lourenço EV, Wong M, Hahn BH, Palma-Diaz MF, Skaggs BJ: Laquinimod delays and suppresses nephritis in lupus-prone mice and affects both myeloid and lymphoid immune cells. Arthritis Rheum (Munch) 66: 674–685, 2014
84. Jayne D, Appel G, Chan TM, Barkay H, Weiss R, Wofsy D: A randomized controlled study of laquinimod in active lupus nephritis patients in combination with standard care. Ann Rheum Dis 72[Suppl 3]: A164, 2013
85. Phoon RK, Kitching AR, Odobasic D, Jones LK, Semple TJ, Holdsworth SR: T-bet deficiency attenuates renal injury in experimental crescentic glomerulonephritis. J Am Soc Nephrol 19: 477–485, 2008
86. Tipping PG, Holdsworth SR: Cytokines
in glomerulonephritis. Semin Nephrol 27: 275–285, 2007
87. Paust HJ, Turner JE, Steinmetz OM, Peters A, Heymann F, Hölscher C, Wolf G, Kurts C, Mittrücker HW, Stahl RA, Panzer U: The IL-23/Th17 axis contributes to renal injury in experimental glomerulonephritis. J Am Soc Nephrol 20: 969–979, 2009
88. Odobasic D, Gan PY, Summers SA, Semple TJ, Muljadi RC, Iwakura Y, Kitching AR, Holdsworth SR: Interleukin-17A promotes early but attenuates established disease in crescentic glomerulonephritis in mice. Am J Pathol 179: 1188–1198, 2011
89. Steinmetz OM, Summers SA, Gan PY, Semple T, Holdsworth SR, Kitching AR: The Th17-defining transcription factor RORγt promotes glomerulonephritis. J Am Soc Nephrol 22: 472–483, 2011
90. Summers SA, Steinmetz OM, Li M, Kausman JY, Semple T, Edgtton KL, Borza DB, Braley H, Holdsworth SR, Kitching AR: Th1 and Th17 cells induce proliferative glomerulonephritis. J Am Soc Nephrol 20: 2518–2524, 2009
91. Wolf D, Hochegger K, Wolf AM, Rumpold HF, Gastl G, Tilg H, Mayer G, Gunsilius E, Rosenkranz AR: CD4+CD25+ regulatory T cells inhibit experimental anti-glomerular basement membrane glomerulonephritis in mice. J Am Soc Nephrol 16: 1360–1370, 2005
92. Eller K, Wolf D, Huber JM, Metz M, Mayer G, McKenzie AN, Maurer M, Rosenkranz AR, Wolf AM: IL-9 production by regulatory T cells recruits mast cells that are essential for regulatory T cell-induced immune suppression. J Immunol 186: 83–91, 2011
93. King WJ, Brooks CJ, Holder R, Hughes P, Adu D, Savage CO: T lymphocyte responses to anti-neutrophil cytoplasmic autoantibody (ANCA) antigens are present in patients with ANCA-associated systemic vasculitis and persist during disease remission. Clin Exp Immunol 112: 539–546, 1998
94. Schmitt WH, Hagen EC, Neumann I, Nowack R, Flores-Suárez LF, van der Woude FJ; European Vasculitis Study Group: Treatment of refractory Wegener’s granulomatosis with antithymocyte globulin (ATG): An open study in 15 patients. Kidney Int 65: 1440–1448, 2004
95. Csernok E, Trabandt A, Müller A, Wang GC, Moosig F, Paulsen J, Schnabel A, Gross WL: Cytokine profiles in Wegener’s granulomatosis: Predominance of type 1 (Th1) in the granulomatous inflammation. Arthritis Rheum 42: 742–750, 1999
96. Nogueira E, Hamour S, Sawant D, Henderson S, Mansfield N, Chavele KM, Pusey CD, Salama AD: Serum IL-17 and IL-23 levels and autoantigen-specific Th17 cells are elevated in patients with ANCA-associated vasculitis. Nephrol Dial Transplant 25: 2209–2217, 2010
97. Chavele KM, Shukla D, Keteepe-Arachi T, Seidel JA, Fuchs D, Pusey CD, Salama AD: Regulation of myeloperoxidase-specific T cell responses during disease remission in antineutrophil cytoplasmic antibody-associated vasculitis: The role of Treg cells and tryptophan degradation. Arthritis Rheum 62: 1539–1548, 2010
98. Velden J, Paust HJ, Hoxha E, Turner JE, Steinmetz OM, Wolf G, Jabs WJ, Özcan F, Beige J, Heering PJ, Schröder S, Kneißler U, Disteldorf E, Mittrücker HW, Stahl RA, Helmchen U, Panzer U: Renal IL-17 expression in human ANCA-associated glomerulonephritis. Am J Physiol Renal Physiol 302: F1663–F1673, 2012
99. Gan PY, Steinmetz OM, Tan DS, O’Sullivan KM, Ooi JD, Iwakura Y, Kitching AR, Holdsworth SR: Th17 cells promote autoimmune anti-myeloperoxidase glomerulonephritis. J Am Soc Nephrol 21: 925–931, 2010
100. Little MA, Bhangal G, Smyth CL, Nakada MT, Cook HT, Nourshargh S, Pusey CD: Therapeutic effect of anti-TNF-alpha antibodies in an experimental model of anti-neutrophil cytoplasm antibody-associated systemic vasculitis. J Am Soc Nephrol 17: 160–169, 2006
101. Wegener’s Granulomatosis Etanercept Trial (WGET) Research Group: Etanercept plus standard therapy for Wegener’s granulomatosis. N Engl J Med 352: 351–361, 2005
102. Laurino S, Chaudhry A, Booth A, Conte G, Jayne D: Prospective study of TNFalpha blockade with adalimumab in ANCA-associated systemic vasculitis with renal involvement. Nephrol Dial Transplant 25: 3307–3314, 2010