Role of C3a Receptors, C5a Receptors, and Complement Protein C6 Deficiency in Collagen Antibody-Induced Arthritis in Mice

Abstract

The complement system, especially the alternative pathway (AP), plays essential roles in the induction of injury in collagen antibody-induced arthritis (CAIA) in mice. The goal of the current study was to directly compare the roles of receptors for C3a and C5a, as well as the membrane attack complex (MAC), as effector mechanisms in the pathogenesis of CAIA. Clinical disease activity (CDA) in C3aR−/−, C5aR−/−, and C6 deficient (C6-def) mice was decreased by 52%, 94%, and 65%, respectively, as compared with WT mice. Decreases in histopathologic injury as well as in IgG and C3 deposition paralleled the CDA. A decrease in the percentage of synovial neutrophils was observed in C3aR−/−, C5aR−/−, and C6-def mice, and a decrease in macrophages was observed in C3aR−/− and C5aR−/−, but not in C6-def, mice. Synovial mRNA obtained by laser capture microdissection exhibited a decrease in TNF-α in C5aR−/− mice and in IL-1β in both C5aR−/− and C6-def mice, while C3aR−/− mice demonstrated no change in either cytokine. Our findings show that absent C3aR-, C5aR- or MAC-initiated effector mechanisms each decreases susceptibility to CAIA, with clinical effects most pronounced in C5aR deficient mice. Although the absence of C3aR, C5aR, or C6 led to differential deficiencies in effector mechanisms, decreased proximal joint IgG and C3 deposition was common to all three genotypes in comparison to WT mice. These data suggest the existence of positive feedback amplification pathways downstream of all three effectors that promote additional IgG deposition and C3 activation in the joint.

Rapid-onset clinical and mechanistic effects of anti-C5aR treatment in the mouse collagen-induced arthritis model

“…Together, these data demonstrate that one mechanism of action of anti-mC5aR may be through reduction of myeloid cell influx into the joint, which is in agreement with the known function of C5a as a potent chemotactic factor. Reduced numbers of infiltrating myeloid cells have been demonstrated in C5aR-deficient mice in the CAIA model and after 10 days of treatment in anti-C5 mAbtreated mice in the CIA model, but again our data are the first to demonstrate that this is an early effect of C5aR blockade [21,22,24]. Part of the reduced levels of inflammatory mediators may be secondary to the reduced myeloid cell infiltration, but this does not rule out that C5a also activate infiltrated cells directly and induce the level of inflammatory mediators and chemokines.…”

“…Together, KC, MCP-1 and MCP-5 have the potential of recruiting a panel of inflammatory cells such as neutrophils, monocytes, macrophages, dendritic cells and lymphocytes into inflammatory sites [41,42]. Reduced levels of MPO, TNF-α, IL-1β, MMP-3 and MIP-1a, MIP-2 have been demonstrated in C5aR-deficient mice in the collagen antibody-induced arthritis (CAIA) model, but our data are the first to demonstrate that this is an early therapeutic effect of C5aR blockade [21,24]. Immunohistochemical stainings demonstrated a reduced influx of neutrophils and macrophages in paws 48 h after single-dose treatment.…”

“…In the collagen antibody-induced arthritis model C5aR-deficient mice were resistant to disease [24]. Also in other arthritis models, C5aR blockade has been demonstrated to be beneficial: anti-C5aR monoclonal antibodies were therapeutically efficacious in the K/B × N serum transfer mouse model of arthritis [25], oral treatment with a small molecule C5aR antagonist reduced joint damage in the rat antigen-induced arthritis model [26] and C5aR-deficient mice exhibited reduced disease in the SKG model of arthritis [27].…”

Is the Complement Activation Product C3a a Proinflammatory Molecule? Re-evaluating the Evidence and the Myth

“…This suggests that, in the chronic phase of inflammation, where monocyte/macrophage responses become more predominant over neutrophils, C3a may indeed act as a classical proinflammatory mediator. This view is supported by evidence that C3ar1 2/2 animals have modest pathology reductions in chronic disease models, such as rheumatoid arthritis (40). In contrast to the effects of C3a on purified monocytes (39), in vitro investigations into the effects of C3a on LPSinduced cytokine release by PBMCs demonstrate differences in action depending on the phenotype of the cell.…”

Treatment with anti-C5aR mAb leads to early-onset clinical and mechanistic effects in the murine delayed-type hypersensitivity arthritis model

“…A vaccine that induces generation of anti-C5a antibodies has been shown to be effective in murine collagen-induced arthritis (CIA) in mice [16], and oral treatment with a small molecule C5a antagonist reduced joint damage in the rat antigen-induced arthritis model [17]. In several mouse models of arthritis C5aR-deficient mice show reduced disease development [18][19][20][21]. In human C5aR knockin mice, a mouse anti-human C5aR monoclonal antibody effectively ameliorated neutrophil-dependent K/B Â N serum transfer-induced arthritis [22], and it has been shown that antimouse C5aR mAb lowers disease activity when administered in the early stages of murine CIA [23].…”