Sepsis remains a significant problem in health care. Despite the establishment and reinforcement of standardized approach toward sepsis worldwide, the recent report suggested that the mortality still remains greater than 30% in Europe and North America (1), arguing for the further need of its pathophysiological exploration.
Macrophage 1 antigen (Mac-1, CD11bCD18, complement receptor 3) is a promiscuous leukocyte adhesion receptor that interacts with multiple ligands such as intercellular adhesion molecule 1 (ICAM-1), iC3b, fibrinogen, and factor X. It is involved in leukocyte recruitment (2), phagocytosis (3), and neutrophil apoptosis (4, 5). Because of its multifaceted functions in the immune system, the role of this molecule in infection has been previously explored. Macrophage 1 antigen–deficient mice demonstrated poorer bacterial clearance and outcomes in Escherichia coli (6) and Streptococcus pneumoniae infection (7). Mice carrying the point mutation of fibrinogen, which disrupted only the interaction of Mac-1 and fibrinogen also demonstrated the reduced clearance of Staphylococcus aureus infection (8). These studies suggest that complete or partial loss of Mac-1 function is disadvantageous in bacterial clearance. In polymicrobial abdominal sepsis model, however, Mac-1–blocking antibody M1/70 antibody attenuated lung injury, one of the significant morbidities associated with sepsis (9). The latter study was performed using relatively milder sepsis model, and whether the beneficial effect on lung injury is still present in more severe sepsis is not clear. In addition, the hindrance of bacterial clearance through the blockade of Mac-1 may be detrimental if sepsis is severe.
The use of blocking antibody can be sometimes problematic in understanding the role of the target molecule. For example, an antibody against CD11b may interfere sterically a receptor in a close vicinity. The binding of antibodies to neutrophils may activate them through Fc receptors to change their functions (10). Taken together, we evaluated the role of Mac-1 in severe polymicrobial sepsis model using Mac-1–deficient mice.
MATERIALS AND METHODS
CD11b knockout (KO) mice (Mac-1–deficient mice) generated by gene targeting have been previously described (4). Mice were purchased from Jackson laboratory and inbred in our animal facilities. All mice were of C57BL/6 J background and housed under specific pathogen-free conditions, 12-h bright and dark cycles. Only male mice at 8 to 10 weeks of age were utilized for the experiments.
Cecal ligation and puncture model
All the experiments were approved by the investigational review board and adhered to the Animal Research Reporting In Vivo Experiments guidelines. Polymicrobial sepsis was induced by cecal ligation and puncture (CLP) following ketamine 60 mg/kg and xylazine 5 mg/kg anesthesia as previously described (11, 12). The cecum was exteriorized, ligated at 1.0 cm from its tip, and subjected to a single, through-and-through puncture using an 18-gauge needle. A small amount of fecal material was expelled with gentle pressure to maintain the patency of puncture sites. The abdomen was closed, and 0.1 mL/kg of warmed saline was administered subcutaneously. Buprenorphine was given subcutaneously to alleviate postoperative surgical pain.
Quantitative assessment of tissue bacterial load
The organ tissues were weighed and homogenized into 1 mL of sterile phosphate-buffered saline (PBS). Aliquots of these tissue suspensions were serially diluted, plated on 5% blood agar plates (Teknova; Hollister, Calif), and incubated for 18 h. All the colonies were counted on the plates.
Assessment of leukocyte recruitment to the abdominal cavity
At 6 and 12 h after CLP, mice were killed, and peritoneal lavage was performed by injecting 3 mL cold sterile PBS into the abdomen and aspirating the peritoneal fluid. The number of peritoneal leukocytes was counted using TURK blood-diluting fluid (Ricca Chemical, Arlington, Tex). In addition, peritoneal leukocytes were subject to Giemsa staining using Heme 3 kit (Thermo Fischer Scientific, Cambridge, Mass) to evaluate the differential of leukocytes.
Plasma enhanced bacterial killing assay
Neutrophils were isolated from mouse bone marrow as previously described (13). Fifty percent diluted plasma from wild-type (WT) or Mac-1–deficient mice was incubated with an equal volume of bacteria (2 × 105 colony-forming units) at 37°C for 30 min to opsonize the bacteria. Bacteria were obtained from cecal flora. The opsonization was stopped by placing the mixture on ice for 1 h. The neutrophils (2 × 104 cells) were mixed with the opsonized bacteria and incubated at 37°C for 1 h. The mixture was plated on blood agar and incubated for 18 h. The number of bacterial colonies was determined.
Complete blood count and serum cytokine measurement
Complete blood count was measured using VetScan HM2 (Abaxis, Union City, Calif). Serum interferon γ (IFN-γ), interleukin 1β (IL-1β), IL-2, IL-4, IL-5, keratinocyte chemoattractant, IL-10, IL-12, and tumor necrosis factor α (TNF-α) levels were measured using mouse TH1/TH2 9-plex ultrasensitive kit (Meso Scale Discovery; Gaithersburg, Md) per the company protocol.
Western blot analysis
The total protein from mouse tissues or primary splenocytes was extracted in a lysis buffer containing proteinase inhibitors (Roche Applied Science, Indianapolis, Ind). Total protein concentrations were determined using BCA protein assay (Fisher Scientific, Morris Plains, NJ). Equal amount of proteins was resolved by 12% sodium dodecyl sulfate–polyacrylamide gel electrophoresis and transferred to nitrocellulose membranes. After blocking in 5% nonfat dry milk, the membranes were incubated with anti–cleaved caspase 3 antibody, anti–caspase 8 antibody, anti–caspase 9 antibody, or anti–β-actin antibody (Cell Signaling Technology, Danvers, Mass). Membranes were then incubated with anti–rabbit immunoglobulin G horseradish peroxidase conjugate. Immunoreactive proteins were visualized by enhanced chemiluminescence (Thermo Scientific, Waltham, Mass).
Mice were anesthetized with isoflurane and underwent transcardiac puncture for perfusion with PBS, followed cold 4% paraformaldehyde. Tissues were embedded in paraffin wax after graded ethanol and xylene treatment. The tissue blocks were cut into 5-μm sections and mounted on slides for staining.
Cleaved caspase 3 immunohistochemistry in spleen tissue
Immunohistochemistry for cleaved caspase 3 was performed to assess apoptosis as described previously (14). The sections of spleen tissues were deparaffinized in xylene and rehydrated through graded alcohol. Endogenous peroxidases were inactivated by immersing the sections in 3.0% hydrogen peroxide and heated in citrate buffer (pH 6.0) at 95°C to 100°C. After washing and blocking, the sections were incubated with anti–cleaved caspase 3 antibody. Then, they were incubated with biotinylated anti–rabbit immunoglobulin G (Dako, Carpinteria, Calif), followed by peroxidase-conjugated streptavidin. The chromogenic reaction was developed with 3,3′-diaminobenzidine for 3 min, and all sections were counterstained with hematoxylin.
TUNEL staining in spleen tissue
Apoptosis was also determined using the terminal deoxynucleotidyl-transferase–mediated 2′-deoxyuridine 5′-triphosphate nick end labeling per the company protocol (Millipore, Serological Corporation, Norcross, Ga). Briefly, the spleen slices were deparaffinized in xylene and rehydrated through graded alcohol, treated with proteinase K (20 μg/mL) (Roche Applied Science), quenched in 3.0% hydrogen peroxide in PBS, incubated in equilibration buffer, and labeled with terminal deoxynucleotidyl-transferase reaction mix. The slides were then incubated with antidigoxigenin conjugate and colorized with DAB. All sections were counterstained with hematoxylin.
After the animals were killed, the chest was open to visualize lungs. The trachea was cannulated using an 18-gauge intravenous catheter and instilled with 1 mL of PBS/0.5 mM EDTA two times. Recovered fluid was centrifuged, and pellets were suspended in PBS. The number of leukocytes was counted using TURK blood-diluting fluid. In addition, leukocytes were stained with Heme 3 kit to obtain the differential of leukocytes.
Myeloperoxidase activity assay
Myeloperoxidase assay was performed as previously described (15). Briefly, mice were killed 12 h after CLP procedure, and the body was flushed with PBS through the pulmonary artery. Lung was removed, immediately snap frozen, and stored at −80°C until use. Frozen lung was thawed, homogenized, and resuspended in 50 mM KPO4 buffer (pH 6.0) containing 0.5% hexadecyltrimethylammonium bromide and was incubated at 60°C for 2 h. Following three freeze-thaw cycles, samples were centrifuged, and supernatant was subject to analysis with the addition of o-dianisodine and H2O2. Absorbance was measured at 450 nm.
Statistical analysis was performed using PRISM5 software (GraphPad software, Inc, La Jolla, Calif). Statistical methods used were described in corresponding figure legends. P < 0.05 was considered statistically significant.
Mac-1 deficiency was associated with poorer outcomes in polymicrobial abdominal sepsis
We studied sepsis with more severity than in the previous study (9). The mortality of KO mice was significantly higher than that of WT (survival percentage WT 43.5% vs. KO 13.0%; P = 0.0038) (Fig. 1). Macrophage 1 antigen is involved in phagocytosis, leukocyte recruitment, and apoptosis, and we explored which was responsible for this outcome.
Mac-1 deficiency was associated with higher bacterial load
Macrophage 1 antigen is involved in both complement- and Fc receptor– mediated phagocytosis (16, 17). Complete or partial loss of Mac-1 function was associated with poorer bacterial clearance in other infectious models (6, 7). As seen in Figure 2A, bacterial load in blood was higher in KO mice even at 6 h after CLP. Using the peritoneal emigration ratio defined as [peritoneal leukocyte number / peripheral leukocyte number] by Prince et al. (7), the recruitment of leukocyte recruitment to the abdominal cavity was rather enhanced in KO mice (Fig. 2B), suggesting that higher bacterial load might be due to the impairment of bacterial killing process in KO mice. Although CD11a and CD49d are largely responsible for leukocyte recruitment to the abdominal cavity, there was no significant change of surface CD11a and CD49d expression in KO mice (data not shown). The mechanism of enhanced leukocyte recruitment to the abdominal space in KO mice remains to be determined.
Peritoneal neutrophils demonstrated a significant impairment of bacterial phagocytosis in Mac-1–deficient mice
We compared the capability of bacterial killing between WT and KO mice. Contrary to our prediction, the serum of KO mice killed bacteria more efficiently than that of WT (Fig. 3A). Although KO neutrophils were less efficient than WT neutrophils, the combination of WT serum and WT neutrophils was as efficient in bacterial killing as the combination of KO serum and KO neutrophils, implying that both strains could eradicate bacteria similarly within the bloodstream. However, peritoneal neutrophils of KO mice demonstrated a significant phagocytic defect following CLP (Fig. 3B). Inefficient bacterial phagocytosis in the peritoneal cavity is likely to explain higher bacterial load in KO mice.
More proinflammatory response in Mac-1–deficient mice
Because Mac-1 deficiency was associated with higher bacterial load in blood and worse outcome, we speculated that KO mice would demonstrate higher proinflammatory cytokine levels. As expected, the levels of proinflammatory cytokine such as IFN-γ and IL-1β were higher in KO mice (Fig. 4). Tumor necrosis factor α was also higher, although statistically not significant. These are in line with the outcome results.
More apoptosis was observed in spleen of Mac-1–deficient mice
Apoptosis in splenocytes is the phenotype associated with sepsis (18). The improvement of sepsis outcome by the administration of antiapoptotic drugs was previously reported (19, 20), suggesting that the degree of apoptosis might represent the severity of sepsis. Inducers of apoptosis such as proinflammatory cytokines and bacterial loads existed significantly more in KO mice (21, 22). In neutrophils, Mac-1 deficiency is associated with the reduction of apoptosis (4). To understand the role of Mac-1 in apoptosis in sepsis, we compared the expression of cleaved caspase 3 at three different time points using Western blot analysis. Its expression was highest at 12 h after CLP surgery for both WT and KO mice (Fig. 5, A and B). Knockout mice showed higher expression at both 12 and 24 h. The analysis of cleaved caspases 8 and 9 suggested that both extrinsic and intrinsic pathways were involved in the enhanced apoptosis in KO mice. Interestingly, baseline cleaved caspases’ levels were higher in KO mice. Increased apoptosis in KO mice was also confirmed on the histology section using TUNEL and cleaved caspase 3 staining (Fig. 6, A and B). Our data demonstrated that Mac-1 deficiency did not attenuate, but rather enhanced splenic apoptosis. Apoptosis was largely seen in the follicular region of spleen where T and B cells were abundant (Fig. 6, C and D). Subsets of T and B cells express Mac-1 (23, 24). Next, we induced apoptosis using staurosporine in primary splenocytes. Knockout splenocytes showed higher apoptosis at the same concentrations of staurosporine than WT, suggesting that they were prone to apoptosis (Fig. 6E). We noted that the expression of cleaved caspase 3 without staurosporine was more elevated in KO mice, which is compatible with the previous tissue result. The underlying mechanism remains to be determined.
Neutrophil recruitment to lung parenchyma was not reduced in Mac-1–deficient mice
Macrophage 1 antigen also plays a role in neutrophil recruitment. In sepsis, exaggerated neutrophil recruitment to organs can pose tissue injury, and lung injury is one of the most serious complications. Neutrophil recruitment to both lung and alveolar space was examined at 12 h after CLP procedure. Macrophage 1 antigen deficiency did reduce neutrophil recruitment to alveolar space, although statistically insignificant, but it did not decrease to lung parenchyma (Fig. 7, A and 7B). Of note, baseline peripheral blood neutrophil counts did not demonstrate any difference between WT and KO mice (Fig. 8).
Here we demonstrated that Mac-1–deficient mice had poorer outcomes in polymicrobial sepsis associated with higher bacterial load in blood, more severe systemic inflammation, and predisposition to apoptosis. Contrary to the previous report using anti–CD11b-blocking antibody (9), neutrophil recruitment to lung was not attenuated in Mac-1 deficiency in more severe polymicrobial abdominal sepsis model.
Lung injury is one of the major complications in sepsis and associated with a high mortality (25). Potential candidates to modulate neutrophil recruitment to lung including adhesion molecules have been extensively studied mainly using blocking antibodies and KO mice (26). However, some of the reported results have been inconsistent. For example, P-selectin and ICAM-1 KO mice did not show any reduction in neutrophil sequestration in acute lung injury model, whereas the administration of anti–P-selectin or anti–ICAM-1 antibody attenuated it (27). The administration of antibodies against other adhesion molecules E-selectin and L-selectin also attenuated (26). In lung, neutrophils transmigrate via capillary bed (26) without rolling (in which selectins are major players) (28), suggesting that the reported results of attenuated neutrophil recruitment by antibodies against selectins may be related to the use of antibodies themselves. The study of distribution pattern of intravenously injected anti–CD11a-blocking antibody, antibody against a sister molecule of CD11b, demonstrated that it was largely seen in liver and spleen, followed by in blood (29). The antibody trapped in these organs may bind to and trap neutrophils there. If this is the case, there is a possibility that the observed beneficial effects can be simply due to the redistribution of neutrophils through antibodies. Therefore, the study examined by blocking antibody should be supplemented with the study using KO mice. As shown in our study, Mac-1 deficiency did not attenuate the recruitment of neutrophils to lung, suggesting that blocking Mac-1 is likely not to be beneficial.
The role of Mac-1 in polymicrobial sepsis is quite complex as demonstrated in our study. For example, TNF-α and IL-1β levels were higher in Mac-1–deficient mice than WT mice in our study, whereas deficiency of its counterligand ICAM-1 was associated with a significant reduction in TNF-α and IL-1β levels (30). This implies that the result of these proinflammatory cytokines in Mac-1–deficient mice cannot be explained simply from the interaction between Mac-1 and ICAM-1. Macrophage 1 antigen is suggested to have a regulatory role on Toll-like receptor 4 (TLR4) signaling, and Mac-1 deficiency enhances TLR-mediated responses in macrophages (6). In conjunction with increased bacterial load in the polymicrobial sepsis model, it is assumed that in Mac-1–deficient mice, more TNF-α and IL-1β are produced through exaggerated activation of TLR4 on macrophages. However, the underlying mechanism of reduced TNF-α level in ICAM-1 KO mice is unclear and remains to be determined. Macrophage 1 antigen expression level in lymphocytes is relatively low, and the levels of IL-2, IL-4, IL-5, and IL-12, mainly produced by lymphocytes, were not significantly different between WT and KO mice. Interestingly, we found that IFN-γ was also elevated in Mac-1–deficient mice. Interferon γ is largely produced by T cells and natural killer cells (NK cells). The study by Varma et al. (31) demonstrated that under endotoxin exposure about 60% of IFN-γ–producing cells are NK cells, and 20% to 25% of cells are NK T cells. T cell–independent production of IFN-γ is induced by the combination of TNF-α and second products, which may be of bacterial origin (32). Higher TNF-α and bacteria levels might explain the higher IFN-γ level in KO mice.
Notably, we found that the spleen of Mac-1–deficient mice had more cleaved caspase 3 level even at the baseline, suggesting that Mac-1 deficiency is prone to apoptosis in the spleen even without sepsis. This may be disadvantageous in sepsis. In neutrophils, Mac-1 deficiency is associated with less apoptosis (4). The role of Mac-1 in different cell types needs further clarification.
Then, is there any benefit derived from the blockade of Mac-1 function? Our study of polymicrobial sepsis did not demonstrate any beneficial aspect of Mac-1 deficiency. One of the issues related to Mac-1 is that (a) it interacts with a variety of seemingly unrelated ligands, and (b) ligands that Mac-1 bind to can interact with other adhesion molecules, suggesting the presence of functional redundancy. As the latter examples, ICAM-1 binds to leukocyte function-associated antigen 1 (LFA-1, CD11aCD18), iC3b binds to αxβ2 (CD11cCD18), and fibrinogen binds to platelet receptor αIIbβ3. So far, the study of directly evaluating the interaction of Mac-1 with each individual ligand in vivo is limited. The study using mice with the point mutation to abolish the interaction between Mac-1 and fibrinogen (without impairing the interaction of fibrinogen with αIIbβ3) demonstrated that the obliteration of Mac-1/fibrinogen binding significantly impaired bacterial clearance (8). In contrast, ICAM-1 KO mice, for example, improved the survival with less liver injury in CLP sepsis model (30). Considering that LFA-1 is not involved in neutrophil recruitment to liver (33), the attenuation of liver injury in ICAM-1 KO mice may represent potential benefit of blocking Mac-1. Intercellular adhesion molecule 1 binds to Mac-1 through its domain 3, whereas it binds to LFA-1 through its domain 1 (34). Therefore, mutation of domain 3 to impair its interaction with Mac-1 only may decipher the impact of Mac-1–ICAM-1 interaction. Understanding the impact of Mac-1 with an individual ligand or Mac-1 itself will allow us to open the door for potential interventions.
The domain called “the I domain” in Mac-1 is the major recognition site(s) of ligands (35). The mutagenesis studies suggest that the binding site of each ligand is overlapping but not exactly the same (36). Unfortunately, x-ray crystallographic I domain (Mac-1) structure coupled with the ligands is available only for iC3b (37), and we have not yet understood the detailed structural difference in the interactions of Mac-1 with various ligands. Once we understand the difference, developing antagonist(s) that specifically inhibits a particular interaction may provide a therapeutic potential.
In conclusion, Mac-1 deficiency was associated with poorer outcomes, more bacterial load, systemic inflammation, and splenic apoptosis. However, Mac-1 deficiency was not associated with the reduction of neutrophil recruitment to lung.
1. Levy MM, Artigas A, Phillips GS, Rhodes A, Beale R, Osborn T, Vincent JL, Townsend S, Lemeshow S, Dellinger RP: Outcomes of the Surviving Sepsis Campaign in intensive care units in the USA and Europe: a prospective cohort study. Lancet Infect Dis
12 (12): 919–924, 2012.
2. Dunne JL, Ballantyne CM, Beaudet AL, Ley K: Control of leukocyte rolling velocity in TNF-alpha–induced inflammation by LFA-1 and Mac-1. Blood
99 (1): 336–341, 2002.
3. Harris ES, McIntyre TM, Prescott SM, Zimmerman GA: The leukocyte integrins. J Biol Chem
275 (31): 23409–23412, 2000.
4. Coxon A, Rieu P, Barkalow FJ, Askari S, Sharpe AH, von Andrian UH, Arnaout MA, Mayadas TN: A novel role for the beta 2 integrin CD11b/CD18 in neutrophil apoptosis
: a homeostatic mechanism in inflammation. Immunity
5 (6): 653–666, 1996.
5. Mayadas TN, Cullere X: Neutrophil beta2 integrins: moderators of life or death decisions. Trends Immunol
26 (7): 388–395, 2005.
6. Han C, Jin J, Xu S, Liu H, Li N, Cao X: Integrin CD11b negatively regulates TLR-triggered inflammatory responses by activating Syk and promoting degradation of MyD88 and TRIF via Cbl-b. Nat Immunol
11 (8): 734–742, 2010.
7. Prince JE, Brayton CF, Fossett MC, Durand JA, Kaplan SL, Smith CW, Ballantyne CM: The differential roles of LFA-1 and Mac-1 in host defense against systemic infection with Streptococcus pneumoniae
. J Immunol
166 (12): 7362–7369, 2001.
8. Flick MJ, Du X, Witte DP, Jirouskova M, Soloviev DA, Busuttil SJ, Plow EF, Degen JL: Leukocyte engagement of fibrin(ogen) via the integrin receptor alphaMbeta2/Mac-1 is critical for host inflammatory response in vivo
. J Clin Invest
113 (11): 1596–1606, 2004.
9. Asaduzzaman M, Zhang S, Lavasani S, Wang Y, Thorlacius H: LFA-1 and MAC-1 mediate pulmonary recruitment of neutrophils and tissue damage in abdominal sepsis. Shock
30 (3): 254–259, 2008.
10. Zhou M, Todd RF 3rd, van de Winkel JG, Petty HR: Cocapping of the leukoadhesin molecules complement receptor type 3 and lymphocyte function-associated antigen-1 with Fc gamma receptor III on human neutrophils. Possible role of lectin-like interactions. J Immunol
150 (7): 3030–3041, 1993.
11. Rittirsch D, Huber-Lang MS, Flierl MA, Ward PA: Immunodesign of experimental sepsis by cecal ligation and puncture. Nat Protoc
4 (1): 31–36, 2009.
12. Feng Y, Zou L, Zhang M, Li Y, Chen C, Chao W: MyD88 and Trif signaling play distinct roles in cardiac dysfunction and mortality during endotoxin shock and polymicrobial sepsis
115 (3): 555–567, 2011.
13. Carbo C, Yuki K, Demers M, Wagner DD, Shimaoka M: Isoflurane inhibits neutrophil recruitment
in the cutaneous Arthus reaction model. J Anesth
27 (2): 261–268, 2013.
14. Liu JR, Liu Q, Li J, Baek C, Han XH, Athiraman U, Soriano SG: Noxious stimulation attenuates ketamine-induced neuroapoptosis in the developing rat brain. Anesthesiology
117 (1): 64–71, 2012.
15. Hoesel LM, Neff TA, Neff SB, Younger JG, Olle EW, Gao H, Pianko MJ, Bernacki KD, Sarma JV, Ward PA: Harmful and protective roles of neutrophils in sepsis. Shock
24 (1): 40–47, 2005.
16. Jongstra-Bilen J, Harrison R, Grinstein S: Fcgamma-receptors induce Mac-1 (CD11b/CD18) mobilization and accumulation in the phagocytic cup for optimal phagocytosis
. J Biol Chem
278 (46): 45720–45729, 2003.
17. Ehlers MR: CR3: a general purpose adhesion-recognition receptor essential for innate immunity. Microbes Infect
2 (3): 289–294, 2000.
18. Hotchkiss RS, Swanson PE, Freeman BD, Tinsley KW, Cobb JP, Matuschak GM, Buchman TG, Karl IE: Apoptotic cell death in patients with sepsis, shock, and multiple organ dysfunction. Crit Care Med
27 (7): 1230–1251, 1999.
19. Hotchkiss RS, Chang KC, Swanson PE, Tinsley KW, Hui JJ, Klender P, Xanthoudakis S, Roy S, Black C, Grimm E, et al.: Caspase inhibitors improve survival in sepsis: a critical role of the lymphocyte. Nat Immunol
1 (6): 496–501, 2000.
20. Hotchkiss RS, Tinsley KW, Swanson PE, Chang KC, Cobb JP, Buchman TG, Korsmeyer SJ, Karl IE: Prevention of lymphocyte cell death in sepsis improves survival in mice. Proc Natl Acad Sci U S A
96 (25): 14541–14546, 1999.
21. Ulett GC, Adderson EE: Regulation of apoptosis
by gram-positive bacteria: mechanistic diversity and consequences for immunity. Curr Immunol Rev
2 (2): 119–141, 2006.
22. Wesche DE, Lomas-Neira JL, Perl M, Chung CS, Ayala A: Leukocyte apoptosis
and its significance in sepsis and shock. J Leukoc Biol
78 (2): 325–337, 2005.
23. Wagner C, Hansch GM, Stegmaier S, Denefleh B, Hug F, Schoels M: The complement receptor 3, CR3 (CD11b/CD18), on T lymphocytes: activation-dependent up-regulation and regulatory function. Eur J Immunol
31 (4): 1173–1180, 2001.
24. Ding C, Ma Y, Chen X, Liu M, Cai Y, Hu X, Xiang D, Nath S, Zhang HG, Ye H, et al.: Integrin CD11b negatively regulates BCR signalling to maintain autoreactive B cell tolerance. Nat Commun
4: 2813, 2013.
25. Sevransky JE, Martin GS, Shanholtz C, Mendez-Tellez PA, Pronovost P, Brower R, Needham DM: Mortality in sepsis versus non-sepsis induced acute lung injury. Crit Care
13 (5): R150, 2009.
26. Grommes J, Soehnlein O: Contribution of neutrophils to acute lung injury. Mol Med
17 (3–4): 293–307, 2011.
27. Doerschuk CM, Quinlan WM, Doyle NA, Bullard DC, Vestweber D, Jones ML, Takei F, Ward PA, Beaudet AL: The role of P-selectin and ICAM-1 in acute lung injury as determined using blocking antibodies and mutant mice. J Immunol
157 (10): 4609–4614, 1996.
28. Aird WC: Phenotypic heterogeneity of the endothelium: I. Structure, function, and mechanisms. Circ Res
100 (2): 158–173, 2007.
29. Coffey GP, Fox JA, Pippig S, Palmieri S, Reitz B, Gonzales M, Bakshi A, Padilla-Eagar J, Fielder PJ: Tissue distribution and receptor-mediated clearance of anti-CD11a antibody in mice. Drug Metab Dispos
33 (5): 623–629, 2005.
30. van Griensven M, Probst C, Muller K, Hoevel P, Pape HC: Leukocyte-endothelial interactions via ICAM-1 are detrimental in polymicrobial sepsis
25 (3): 254–259, 2006.
31. Varma TK, Lin CY, Toliver-Kinsky TE, Sherwood ER: Endotoxin-induced gamma interferon production: contributing cell types and key regulatory factors. Clin Diagn Lab Immunol
9 (3): 530–543, 2002.
32. Wherry JC, Schreiber RD, Unanue ER: Regulation of gamma interferon production by natural killer cells in SCID mice: roles of tumor necrosis factor and bacterial stimuli. Infect Immun
59 (5): 1709–1715, 1991.
33. Miyamoto M, Emoto M, Emoto Y, Brinkmann V, Yoshizawa I, Seiler P, Aichele P, Kita E, Kaufmann SH: Neutrophilia in LFA-1–deficient mice confers resistance to listeriosis: possible contribution of granulocyte-colony-stimulating factor and IL-17. J Immunol
170 (10): 5228–5234, 2003.
34. Bella J, Kolatkar PR, Marlor CW, Greve JM, Rossmann MG: The structure of the two amino-terminal domains of human ICAM-1 suggests how it functions as a rhinovirus receptor and as an LFA-1 integrin ligand. Proc Natl Acad Sci U S A
95 (8): 4140–4145, 1998.
35. Diamond MS, Garcia-Aguilar J, Bickford JK, Corbi AL, Springer TA: The I domain is a major recognition site on the leukocyte integrin Mac-1 (CD11b/CD18) for four distinct adhesion ligands. J Cell Biol
120 (4): 1031–1043, 1993.
36. Zhang L, Plow EF: Overlapping, but not identical, sites are involved in the recognition of C3bi, neutrophil inhibitory factor, and adhesive ligands by the alphaMbeta2 integrin. J Biol Chem
271 (30): 18211–18216, 1996.
37. Bajic G, Yatime L, Sim RB, Vorup-Jensen T, Andersen GR: Structural insight on the recognition of surface-bound opsonins by the integrin I domain of complement receptor 3. Proc Natl Acad Sci U S A
110 (41): 16426–16431, 2013.
Keywords:© 2014 by the Shock Society
Macrophage 1 antigen; polymicrobial sepsis; phagocytosis; apoptosis; neutrophil recruitment