CD11b is protective in complement-mediated immune complex glomerulonephritis
Authors: Jessy J. Alexander, Lee D. Chaves, Anthony Chang, Alexander Jacob, Maria Ritchie, Richard J. Quigg
Journal: Kidney International (2015)

In chronic serum sickness, glomerular immune complexes form, yet C57BL/6 mice do not develop glomerulonephritis unless complement factor H (CfH) is absent, indicating the relevance of complement regulation. Complement receptor 3 (CD11b) and Fcγ receptors on leukocytes, and CfH on platelets, can bind immune complexes. Here we induced immune complex–mediated glomerulonephritis in CfH−/− mice chimeric for wild-type, CfH−/−, CD11b−/−, or FcRγ−/− bone marrow stem cells. Glomerulonephritis was worse in CD11b−/− chimeras compared with all others, whereas disease in FcRγ−/− and wild-type chimeras was comparable. Disease tracked strongly with humoral immune responses, but not glomerular immune complex deposits. Interstitial inflammation with M1 macrophages strongly correlated with glomerulonephritis scores. CD11b−/− chimeras had significantly more M1 macrophages and CD4+ T cells. The renal dendritic cell populations originating from bone marrow–derived CD11c+ cells were similar in all experimental groups. CD11b+ cells bearing colony-stimulating factor 1 receptor were present in kidneys, including CD11b−/− chimeras; these cells correlated negatively with glomerulonephritis scores. Thus, experimental immune complex–mediated glomerulonephritis is associated with accumulation of M1 macrophages and CD4+ T cells in kidneys and functional renal insufficiency. Hence, CD11b on mononuclear cells is instrumental in generating an anti-inflammatory response in the inflamed kidney. In chronic serum sickness, glomerular immune complexes form, yet C57BL/6 mice do not develop glomerulonephritis unless complement factor H (CfH) is absent, indicating the relevance of complement regulation. Complement receptor 3 (CD11b) and Fcγ receptors on leukocytes, and CfH on platelets, can bind immune complexes. Here we induced immune complex–mediated glomerulonephritis in CfH−/− mice chimeric for wild-type, CfH−/−, CD11b−/−, or FcRγ−/− bone marrow stem cells. Glomerulonephritis was worse in CD11b−/− chimeras compared with all others, whereas disease in FcRγ−/− and wild-type chimeras was comparable. Disease tracked strongly with humoral immune responses, but not glomerular immune complex deposits. Interstitial inflammation with M1 macrophages strongly correlated with glomerulonephritis scores. CD11b−/− chimeras had significantly more M1 macrophages and CD4+ T cells. The renal dendritic cell populations originating from bone marrow–derived CD11c+ cells were similar in all experimental groups. CD11b+ cells bearing colony-stimulating factor 1 receptor were present in kidneys, including CD11b−/− chimeras; these cells correlated negatively with glomerulonephritis scores. Thus, experimental immune complex–mediated glomerulonephritis is associated with accumulation of M1 macrophages and CD4+ T cells in kidneys and functional renal insufficiency. Hence, CD11b on mononuclear cells is instrumental in generating an anti-inflammatory response in the inflamed kidney. Complement activation through each of the three pathways leads to the generation of C3 and C5 products. These mark infectious microorganisms as foreign and alert innate and adaptive immune cells to their presence. Spontaneous alternative pathway activation is regulated by complement factor H (CfH). When CfH is ineffective in the fluid phase, products of unrestricted C3 activation can deposit in the glomerular capillary wall, as in C3 glomerulopathies.1Fakhouri F. Fremeaux-Bacchi V. Noel L.H. et al.C3 glomerulopathy: a new classification.Nat Rev Nephrol. 2010; 6: 494-499Crossref PubMed Scopus (264) Google Scholar Factor H is also retained by the glomerular and other capillary wall surfaces; when this is inefficient, endothelial cell injury and atypical hemolytic uremic syndrome can result. Anaphylatoxin receptors C3aR and C5aR signal through a subset of pertussis toxin–sensitive GTP-binding protein α-subunits.2Amatruda III, T.T. Gerard N.P. Gerard C. et al.Specific interactions of chemoattractant factor receptors with G-proteins.J Biol Chem. 1993; 268: 10139-10144Abstract Full Text PDF PubMed Google Scholar The β2 integrin (CD18) heterodimers with αM (CD11b) and αX (CD11c) were first termed complement receptors (CR) 3 and 4 by virtue of their binding to inactivated (i) C3b.3Ross G.D. Vetvicka V. CR3 (CD11b, CD18): a phagocyte and NK cell membrane receptor with multiple ligand specificities and functions.Clin Exp Immunol. 1993; 92: 181-184Crossref PubMed Scopus (240) Google Scholar Although traditionally considered adherence receptors, CD11b/CD11c binding to ligand can lead to 'outside-in' signals via immunoreceptor tyrosine-based activation motif proteins; these include the Fc receptor common γ-chain (FcRγ) and DNAX-activating protein of 12 kDa (DAP12) (encoded by Fcer1g and Tyrobp, respectively).4Han C. Jin J. Xu S. et al.Integrin CD11b negatively regulates TLR-triggered inflammatory responses by activating Syk and promoting degradation of MyD88 and TRIF via Cbl-b.Nat Immunol. 2010; 11: 734-742Crossref PubMed Scopus (338) Google Scholar,5Mocsai A. Abram C.L. Jakus Z. et al.Integrin signaling in neutrophils and macrophages uses adaptors containing immunoreceptor tyrosine-based activation motifs.Nat Immunol. 2006; 7: 1326-1333Crossref PubMed Scopus (286) Google Scholar Induction of chronic serum sickness (CSS) leads to deposition of immune complexes (ICs) in glomeruli.6Stilmant M.M. Couser W.G. Cotran R.S. Experimental glomerulonephritis in the mouse associated with mesangial deposition of autologous ferritin immune complexes.Lab Invest. 1975; 32: 746-756PubMed Google Scholar Yet, there is no uniform development of inflammation and glomerulonephritis (GN); for instance, C57BL/6 mice do not develop GN in CSS,7Quigg R.J. Lim A. Haas M. et al.Immune complex glomerulonephritis in C4- and C3-deficient mice.Kidney Int. 1998; 53: 320-330Abstract Full Text PDF PubMed Scopus (93) Google Scholar whereas all CfH-deficient mice with CSS develop diffuse proliferative GN within 5 weeks.8Alexander J.J. Pickering M.C. Haas M. et al.Complement factor H limits immune complex deposition and prevents inflammation and scarring in glomeruli of mice with chronic serum sickness.J Am Soc Nephrol. 2005; 16: 52-57Crossref PubMed Scopus (47) Google Scholar The GN in CSS is characterized by accumulation of IgG/C3-containing ICs together with F4/80+ macrophages.9Alexander J.J. Aneziokoro O.G.B. Chang A. et al.Distinct and separable roles of the complement system in factor H-deficient bone marrow chimeric mice with immune complex disease.J Am Soc Nephrol. 2006; 17: 1354-1361Crossref PubMed Scopus (24) Google Scholar,10Alexander J.J. Chaves L. Chang A. et al.The C5a receptor has a key role in immune complex glomerulonephritis in complement factor H-deficient mice.Kidney Int. 2012; 82: 961-968Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar Disease requires signals through C5aR, as C5aR−/−CfH−/− mice with CSS do not develop GN.10Alexander J.J. Chaves L. Chang A. et al.The C5a receptor has a key role in immune complex glomerulonephritis in complement factor H-deficient mice.Kidney Int. 2012; 82: 961-968Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar Humans use CR1 on erythrocytes for IC processing; in contrast, the rodent relies upon CfH on platelets.11Alexander J.J. Hack B.K. Cunningham P.N. et al.A protein with characteristics of factor H is present on rodent platelets and functions as the immune adherence receptor.J Biol Chem. 2001; 276: 32129-32135Crossref PubMed Scopus (55) Google Scholar,12Ren G. Doshi M. Hack B.K. et al.Rat glomerular epithelial cells produce and bear factor H on their surface which is upregulated under complement attack.Kidney Int. 2003; 64: 914-922Abstract Full Text Full Text PDF PubMed Scopus (18) Google Scholar As such, CfH−/− mice lacking platelet CfH have markedly abnormal IC processing. Platelet CfH is restored in CfH−/− mice chimeric for wild-type bone marrow (BM).9Alexander J.J. Aneziokoro O.G.B. Chang A. et al.Distinct and separable roles of the complement system in factor H-deficient bone marrow chimeric mice with immune complex disease.J Am Soc Nephrol. 2006; 17: 1354-1361Crossref PubMed Scopus (24) Google Scholar These animals still lack hepatic-produced plasma CfH. When CSS is induced in CfH−/− mice with wild-type BM, IC metabolism approaches that in wild-type mice, such that there are considerably fewer glomerular ICs. Yet, these animals still develop GN.9Alexander J.J. Aneziokoro O.G.B. Chang A. et al.Distinct and separable roles of the complement system in factor H-deficient bone marrow chimeric mice with immune complex disease.J Am Soc Nephrol. 2006; 17: 1354-1361Crossref PubMed Scopus (24) Google Scholar In contrast, wild-type mice with CfH−/− BM failed to develop GN, despite the presence of large quantities of ICs (attributable to abnormal IC processing from CfH-deficient platelets).9Alexander J.J. Aneziokoro O.G.B. Chang A. et al.Distinct and separable roles of the complement system in factor H-deficient bone marrow chimeric mice with immune complex disease.J Am Soc Nephrol. 2006; 17: 1354-1361Crossref PubMed Scopus (24) Google Scholar This illustrates the importance of complement regulation by plasma CfH in the setting of glomerular-bound ICs. The abundant ICs containing IgG and iC3b as ligands for inflammatory cell FcγRs and β2 integrins are inert. The presence of active C3b is required to generate C5a as the necessary signal that initiates inflammation in GN.9Alexander J.J. Aneziokoro O.G.B. Chang A. et al.Distinct and separable roles of the complement system in factor H-deficient bone marrow chimeric mice with immune complex disease.J Am Soc Nephrol. 2006; 17: 1354-1361Crossref PubMed Scopus (24) Google Scholar,10Alexander J.J. Chaves L. Chang A. et al.The C5a receptor has a key role in immune complex glomerulonephritis in complement factor H-deficient mice.Kidney Int. 2012; 82: 961-968Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar On the basis of these data, we hypothesized that in CSS-induced GN (1) leukocyte FcγRs and β2 integrins are activated by C5aR signaling; (2) all three are necessary, such that disease will not occur in the absence of any one; (3) although FcγRs and β2 integrins are relevant to systemic IC metabolism, this is of less consequence in this model; and (4) FcγRIII and CD11b were the most likely relevant FcγRs and β2 integrins. To evaluate this, we studied CSS in CfH−/− mice chimeric for FcRγ−/− and CD11b−/− BM. Surprisingly, disease was considerably worse in the latter group. We lethally irradiated CfH−/− mice and reconstituted their BM with CD117+ stem cells from wild-type (n=8), CfH−/− (n=12), FcRγ−/− (n=7), and CD11b−/− (n=7) mice. After stable hematopoeitic cell engraftment, CSS was induced by actively immunizing mice with a daily intraperitoneal dose of 4 mg of horse spleen apoferritin. CfH−/− mice with CfH−/− BM receiving saline vehicle alone were used as control (n=5). As expected, these control CfH−/− chimeras did not generate antibodies to apoferritin. All animals immunized with apoferritin generated an anti-apoferritin antibody response (Figure 1). As predicted from past data,8Alexander J.J. Pickering M.C. Haas M. et al.Complement factor H limits immune complex deposition and prevents inflammation and scarring in glomeruli of mice with chronic serum sickness.J Am Soc Nephrol. 2005; 16: 52-57Crossref PubMed Scopus (47) Google Scholar,9Alexander J.J. Aneziokoro O.G.B. Chang A. et al.Distinct and separable roles of the complement system in factor H-deficient bone marrow chimeric mice with immune complex disease.J Am Soc Nephrol. 2006; 17: 1354-1361Crossref PubMed Scopus (24) Google Scholar CfH−/− chimeras had higher antibody levels than wild-type mice. Yet, the highest levels were observed in the CD11b−/− chimeras (Figure 1, P<0.001). As expected, all animals with CSS had IgG-containing ICs in plasma. Anti-apoferritin IgG levels and ICs were positively correlated (Supplementary Figure S1a online). As with the anti-apoferritin IgG, CfH−/− and CD11b−/− chimeric mice had the highest IC levels compared with wild-type and FcRγ−/− mice. Download .pdf (4.65 MB) Help with pdf files Supplementary Figures We were surprised that CD11b−/− chimeras had the highest anti-apoferritin IgG levels. To examine the role for absent plasma CfH in these findings, we induced CSS in wild-type, CfH−/−, and CD11b−/− mice (i.e., that were not BM chimeras; n=6 each). Serum anti-apoferritin IgG levels were no different between wild-type and CD11b−/− mice (29.5±1.4 and 31.2±1.6 U/ml, respectively). As we have seen before,8Alexander J.J. Pickering M.C. Haas M. et al.Complement factor H limits immune complex deposition and prevents inflammation and scarring in glomeruli of mice with chronic serum sickness.J Am Soc Nephrol. 2005; 16: 52-57Crossref PubMed Scopus (47) Google Scholar CfH−/− mice had higher anti-apoferritin IgG (52.4±4.2, P<0.001 by analysis of variance). These anti-apoferritin IgG levels also strongly correlated with circulating C1q- and IgG-containing ICs (R=0.73), with a slope comparable to the BM chimera studies (0.759 vs. 0.743) (Supplementary Figure S1b online). Thus, the absence of CD11b on BM-derived cells together with absent plasma CfH led to a heightened humoral immune response to the heterologous apoferritin. Because of the absence of plasma CfH in all BM chimeric animals, including controls receiving saline, all mouse glomeruli had strongly positive capillary wall staining for C3 (Figure 2a). The IgG deposits in wild-type chimeric mice were largely within the mesangium, whereas CfH−/− chimeras had strongly positive mesangial IgG (Figure 2a, asterisks), which extended to the peripheral capillary wall. This is attributable to the absence of CfH on platelets, resulting in impaired IC processing in these mice.9Alexander J.J. Aneziokoro O.G.B. Chang A. et al.Distinct and separable roles of the complement system in factor H-deficient bone marrow chimeric mice with immune complex disease.J Am Soc Nephrol. 2006; 17: 1354-1361Crossref PubMed Scopus (24) Google Scholar,11Alexander J.J. Hack B.K. Cunningham P.N. et al.A protein with characteristics of factor H is present on rodent platelets and functions as the immune adherence receptor.J Biol Chem. 2001; 276: 32129-32135Crossref PubMed Scopus (55) Google Scholar The intensity of IgG staining was similar in the three groups with CSS but intact platelet CfH (i.e., wild-type, FcRγ−/−, and CD11b−/−; quantified in Figure 2b), with extension of IgG from the mesangium to the peripheral capillary loops, where it appeared to be present in ICs, as evidenced by dual staining for IgG and C3 (Figure 2a, arrows). In the CD11b−/− chimeric mice, there was greater extension of granular IgG (and C3) deposits into the peripheral capillary wall (Figure 2a, arrowheads). The intensity and localization of IgG within glomeruli in CSS was similar in wild-type, CfH−/−, and CD11b−/− mice relative to their respective BM chimeras (Figure 2c). As with CD11b−/− BM chimeras, CD11b−/− mice had greater peripheral glomerular capillary wall extension of IgG,13Rosetti F. Tsuboi N. Chen K. et al.Human lupus serum induces neutrophil-mediated organ damage in mice that is enabled by Mac-1 deficiency.J Immunol. 2012; 189: 3714-3723Crossref PubMed Scopus (52) Google Scholar although this was not statistically different from wild-type mice. Glomerular C3 staining in wild-type and CD11b−/− mice colocalized with IgG (yellow color in merged images in Figure 2c). In all experimental animals lacking plasma CfH, there was no C3 or IgG staining within the extraglomerular vessels or in the tubulointerstitium. The segmental linear staining for C3 seen in normal mouse peritubular and periglomerular regions was also absent, consistent with the absence of plasma CfH.14Pickering M.C. Cook H.T. Warren J. et al.Uncontrolled C3 activation causes membranoproliferative glomerulonephritis in mice deficient in complement factor H.Nat Genet. 2002; 31: 424-428Crossref PubMed Scopus (416) Google Scholar,15Alexander J.J. Wang Y. Chang A. et al.Mouse podocyte complement factor H - The functional analogue to human complement receptor 1.J Am Soc Nephrol. 2007; 18: 1157-1166Crossref PubMed Scopus (45) Google Scholar Control mice did not develop renal disease, as evidenced by normal blood urea nitrogen (BUN) values (26.1±0.8 mg/dl, Figure 3a). All animals with CSS developed renal insufficiency, with increased BUN values (Figure 3a). Wild-type and FcRγ−/− chimeric mice had comparably increased BUN values (36.5±1.2 and 37.3±1.1 mg/dl, respectively). CfH−/− chimeras with CSS had BUN values (42.7±1.2 mg/dl) that were significantly different from wild type, indicating the relevance of CfH on BM-derived cells. Surprisingly, each of the seven CD11b−/− chimeric mice had higher BUN levels than any of the other 27 animals (Figure 3a) (mean±s.e.m.=53.3±1.5 mg/dl). As we have observed before, anti-apoferritin IgG levels strongly correlated with BUN values (Supplementary Figure S2 online).8Alexander J.J. Pickering M.C. Haas M. et al.Complement factor H limits immune complex deposition and prevents inflammation and scarring in glomeruli of mice with chronic serum sickness.J Am Soc Nephrol. 2005; 16: 52-57Crossref PubMed Scopus (47) Google Scholar Control CfH−/− chimeras receiving saline instead of apoferritin had normal urinary albumin excretion (13.5±1.5 μg/mg creatinine). Albuminuria was 30.5±6.5, 44.3±5.8, and 74.0±4.7 μg/mg creatinine in wild-type, CfH−/−, and CD11b−/− BM chimeras with CSS, respectively (P<0.001, one-way analysis of variance; P<0.03, CD11b−/− vs. all other groups). In CSS induced in native wild-type, CfH−/−, and CD11b−/− mice (i.e., that did not receive BM transfers), urinary albumin was 15.4±1.7, 32.9±2.5, and 26.6±1.6 μg/mg creatinine, respectively (P<0.001, one-way analysis of variance; P<0.005, wild type vs. CfH−/− and CD11b−/−). All animals lacking plasma CfH (i.e., all BM chimeras and CfH−/− mice without BM transfer) in which CSS was induced developed diffuse proliferative GN (Figure 3b). There was little to no interstitial inflammation in any of the groups, except for the CD11b−/− chimeras in which there were focal periglomerular mononuclear cell infiltrates (Figure 3b, arrow). There was no appreciable interstitial fibrosis, tubular atrophy, or arteritis in any kidney. Native wild-type and CD11b−/− mice did not develop GN in CSS (median GN scores 0 and 0.5, respectively; P=0.002 vs. CfH−/− mice studied contemporaneously). Notably, these three measures of renal disease—BUN concentrations, albuminuria, and GN scores—were highly related (R values ⩾0.81, see legend to Supplementary Figure S2 online). BUN and urinary albumin were the most strongly correlated (BUN=20.9+(0.47 × UAlb), R=0.97). It is notable that each measurement is derived from a distinct anatomic site (i.e., blood, urine, and renal tissue). Thus, in this model, the extent of histopathological GN tracks with functional renal disease. In the CSS model, there is IC deposition, complement activation, and inflammation in the glomeruli. Although there is no histopathological evidence of tubulointerstitial nephritis, the mononuclear cell compartment as measured by flow cytometry expands and is related to disease features in this model.10Alexander J.J. Chaves L. Chang A. et al.The C5a receptor has a key role in immune complex glomerulonephritis in complement factor H-deficient mice.Kidney Int. 2012; 82: 961-968Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar Thus, we examined mononuclear cells in the renal interstitium 5 weeks after induction of CSS. There were F4/80+ and CD115+ cells, but not F4/80+CD115+ cells (Supplementary Figure S3 online). The F4/80+ cells were distinguished by CCR2 and Ly6C staining (Figure 4a). There were few Ly6ChiCCR2hi M1 (inflammatory) macrophages in the kidneys of CfH−/− mice with CfH−/− BM, with or without CSS (Figure 4a, red boxes). This is consistent with our past work with CfH−/− mice with CSS.9Alexander J.J. Aneziokoro O.G.B. Chang A. et al.Distinct and separable roles of the complement system in factor H-deficient bone marrow chimeric mice with immune complex disease.J Am Soc Nephrol. 2006; 17: 1354-1361Crossref PubMed Scopus (24) Google Scholar Yet, the wild-type, FcRγ−/−, and CD11b−/− chimeric mice had an increased number of Ly6ChiCCR2hi M1 macrophages (Figure 4a, red arrows), which was significantly greater in CD11b−/− chimeras (Figure 4b). As anticipated, these cells were CD11b- (Figure 4c, red arrowhead). The proportion of F4/80+ cells that were Ly6ChiCCR2hi M1 macrophages positively correlated with GN scores (Figure 5a), supporting that glomerular and tubulointerstitium (TI) inflammation were linked.Figure 5Correlation between tubulointerstitium (TI) mononuclear cells and glomerulonephritis scores. (a) The number of Ly6ChiCCR2hi M1 macrophages as a proportion of all F4/80+ cells positively correlates with glomerulonephritis (GN). The line was fit by least-squares analysis, with the derived equation, GN=0.51+(0.078 × Ly6ChiCCR2hi), R=0.88, P<0.001. (b) The number of CD115+F4/80-CD11b+ cells as a percentage of all CD3-CD19- mononuclear cells negatively correlated with GN. The line was fit by least-squares analysis, with the derived equation, GN=3.4—(0.054 × CD115+), R=-0.84, P<0.001.View Large Image Figure ViewerDownload (PPT) There were also Ly6C+CCR2- cells (Figure 4a, black boxes) comprising two distinct populations, namely Ly6C+CD11b+CD11c- (except in CD11b−/− chimeras) and Ly6ChiCD11b-CD11clo (Supplementary Figure S4 online). The former is consistent with M2 macrophages, whereas the identity of the latter is unclear. The Ly6C- cellular population contained both CCR2- and CCR2+ cells (Figure 4a, blue boxes). Overall, these cells are typical for native kidney dendritic cells.16Soos T.J. Sims T.N. Barisoni L. et al.CX3CR1+ interstitial dendritic cells form a contiguous network throughout the entire kidney.Kidney Int. 2006; 70: 591-596Abstract Full Text Full Text PDF PubMed Scopus (244) Google Scholar,17Hochheiser K. Tittel A. Kurts C. Kidney dendritic cells in acute and chronic renal disease.Int J Exp Pathol. 2011; 92: 193-201Crossref PubMed Scopus (33) Google Scholar The majority were CD11b+CD11c+, although there were different patterns in the different groups (Supplementary Figure S5a online). In the CD11b−/− chimeras, these cells were CD11b- and had greater surface CD11c staining than wild type (Supplementary Figure S5b online). In all groups, the CD115+F4/80- cells were CD11b+CD11c- (Supplementary Figure S3b online), Ly6C-, and CCR2- (data not shown). Interestingly, even CD11b−/− chimeras had these CD115+F4/80-CD11b+ cells, albeit in lesser quantities (Supplementary Figure S3b online). Thus, this particular cellular population is radioresistant. The number of CD115+F4/80-CD11b+ cells negatively correlated with GN scores (Figure 5b) and M1 macrophages (R=-0.86), suggesting this is an anti-inflammatory population. Morever, GN scores in a given animal could be accurately predicted by the two-component model, GN=1.37—(0.044 x CD115+)+(0.047 × BUN) (R=0.92, P<0.001). There were CD3+ T lymphocytes in all kidneys, which were either CD4+ or CD8+ (Figure 6a). Relative to all other groups, the kidneys of CD11b−/− chimeras had an expanded population of CD3+CD4+ cells (Figure 6a, red arrow). This was unique to the kidney in these animals, as the spleens had comparable numbers of lymphocytes (Figure 6b). Thus, the absence of CD11b in either macrophages and/or dendritic cells in mice with experimental GN was associated with increased numbers of CD4+ T lymphocytes within the kidney. In these studies, we induced CSS in CfH−/− BM chimeras. ICs deposited in the glomeruli, around which C3 was activated. In the absence of plasma CfH, active C3b remained, capable of contributing to C5 cleavage.10Alexander J.J. Chaves L. Chang A. et al.The C5a receptor has a key role in immune complex glomerulonephritis in complement factor H-deficient mice.Kidney Int. 2012; 82: 961-968Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar In this setting, all animals developed renal functional impairment and histopathological features of GN. The presence of iC3b and F4/80+ macrophages in inflamed glomeruli9Alexander J.J. Aneziokoro O.G.B. Chang A. et al.Distinct and separable roles of the complement system in factor H-deficient bone marrow chimeric mice with immune complex disease.J Am Soc Nephrol. 2006; 17: 1354-1361Crossref PubMed Scopus (24) Google Scholar,10Alexander J.J. Chaves L. Chang A. et al.The C5a receptor has a key role in immune complex glomerulonephritis in complement factor H-deficient mice.Kidney Int. 2012; 82: 961-968Abstract Full Text Full Text PDF PubMed Scopus (19) Google Scholar supported our hypothesis that CD11b would be pathologic in this model. Unexpectedly, CD11b−/− BM chimeric mice had significantly worse renal disease than any other group. This required the concomitant absence of plasma CfH, as native CD11b−/− mice did not develop GN in CSS. The CSS model used here relies upon repetitive administration with horse spleen apoferritin over 5 weeks, without the use of adjuvant (hence, a nonaccelerated chronic active autologous model). Actively immunized animals generated anti-apoferritin IgG antibodies, which formed ICs with the ongoing source of apoferritin antigen. Thus, it is not surprising that the quantities of circulating ICs were related to anti-apoferritin IgG. The measurement of the former relied upon C1q binding, and it was independent from effects of CfH or CD11b deficiencies on C3. Complement activation in ICs leads to their incorporation of C3b, which bind to cells with specific membrane receptors, a phenomenon termed immune adherence by Nelson.18Nelson D.S. Immune adherence.Adv Immunol. 1963; 3: 131-180Crossref Scopus (87) Google Scholar Rodents, including mice, rely upon CfH on platelets, whereas primates diverged to use CR1 on erythrocytes for this particular immune function. ICs bound to platelet CfH or erythrocyte CR1 are transported to hepatic macrophages for elimination.19Hebert L.A. The clearance of immune complexes from the circulation of man and other primates.Am J Kidney Dis. 1991; 27: 352-361Abstract Full Text PDF Scopus (89) Google Scholar This transfer is believed to occur because these cells bear CR3 and FcγRs. CR3 has a greater binding affinity for ICs bearing iC3b than does CfH (or CR1). In IC processing, it is postulated that FcγRII is the most relevant, as it is inhibitory and does not associate with FcRγ.20Dijstelbloem H.M. van de Winkel J.G. Kallenberg C.G. Inflammation in autoimmunity: receptors for IgG revisited.Trends Immunol. 2001; 22: 510-516Abstract Full Text Full Text PDF PubMed Scopus (163) Google Scholar Consistent with this premise, here we showed that FcRγ−/− BM chimeras had antibody and IC responses comparable to wild-type chimeras. In this disease model, glomerular ICs contain apoferritin, IgG, and C3 components.21Alexander J.J. Hack B.K. Jacob A. et al.Abnormal immune complex processing and spontaneous glomerulonephritis in complement factor H-deficient mice with human complement receptor 1 on erythrocytes.J Immunol. 2010; 185: 3759-3767Crossref PubMed Scopus (10) Google Scholar As in our past studies,9Alexander J.J. Aneziokoro O.G.B. Chang A. et al.Distinct and separable roles of the complement system in factor H-deficient bone marrow chimeric mice with immune complex disease.J Am Soc Nephrol. 2006; 17: 1354-1361Crossref PubMed Scopus (24) Google Scholar excessive glomerular IC deposition occurred when mice lacked platelet CfH, supporting that these formed from deposited ICs. Anti-apoferritin IgG and IgG-containing ICs were highest in CD11b−/− BM chimeric mice; although this did not translate into a higher quantity of total glomerular ICs, qualitatively there was greater extension into the peripheral capillary wall. Yet, CD11b−/− mice with intact CfH were largely indistinguishable from wild-type mice. Similar CD11b-independent IC handling and exaggerated GN was observed by the Mayadas group in an accelerated CSS model.13Rosetti F. Tsuboi N. Chen K. et al.Human lupus serum induces neutrophil-mediated organ damage in mice that is enabled by Mac-1 deficiency.J Immunol. 2012; 189: 3714-3723Crossref PubMed Scopus (52) Google Scholar In their studies, neutrophils preceded macrophages in glomeruli in a CD11b-dependent manner,13Rosetti F. Tsuboi N. Chen K. et al.Human lupus serum induces neutrophil-mediated organ damage in mice that is enabled by Mac-1 deficiency.J Immunol. 2012; 189: 3714-3723Crossref PubMed Scopus (52) Google Scholar a phenomenon that we have not examined. Nonetheless, taking these data together, glomerular IC deposition appears to be largely independent from macrophage IC handling. CfH−/− mice have an abnormally active humoral immune response, which is exaggerated in the absence of CD11b on BM-derived cells. Diverse glomerular diseases are associated with substantial accumulations of mononuclear cells in the TI. In fact, often the strongest predictive variable of glomerular disease outcome is the state of the TI.22Cameron J.S. Tubular and interstitial factors in the progression of glomerulonephritis.Pediatr Nephrol. 1992; 6: 292-303Crossref PubMed Scopus (93) Google Scholar,23Nangaku M. Mechanisms of tubulointerstitial injury in the kidney: final common pathways to end-stage renal failure.Intern Med. 2004; 43: 9-17Crossref PubMed Scopus (279) Google Scholar,24Roberts I.S. Cook H.T. Troyanov S. et al.The Oxford classification of IgA nephropathy: patholo