Development of inflammation in proteoglycan-induced arthritis is dependent on FcγR regulation of the cytokine/chemokine environment

FcgammaRs are specialized cell surface receptors that coordinately regulate immune responses. Although FcgammaR expression is a prerequisite for the development of several immune complex-mediated diseases, the mechanism responsible for FcgammaR-dependent regulation in autoimmunity remains unclear. Therefore, we assessed FcgammaR-dependent regulation of inflammation in proteoglycan-induced arthritis (PGIA) using FcgammaR(-/-) mice. FcgammaRIIb(-/-) mice developed arthritis at an earlier time point and With a greater severity than wild-type (WT) mice. In gamma-chain(-/-) (FcgammaRI(-/-) and FcgammaRIII(-/-)) mice, no clinical or histological evidence of inflammation was observed. Exacerbation of arthritis in FcgammaRIIb(-/-) mice correlated with enhanced PG-specific Ab production, but did not significantly affect PG-specific T cell priming. In gamma-chain(-/-) mice, the absence of arthritis did not correlate with serum Ab responses, as PG-specific Ab production was normal. Although PG-specific T cell proliferation was diminished,,spleen cells from gamma-chain(-/-) mice successfully adoptively transferred arthritis into SCID mice. Our studies indicated that the mechanism responsible for FcgammaR regulation of PGIA development was at the level of inflammatory cytokine and beta-chemokine expression within the joint. FcgammaRIIb regulated the development of PGIA by controlling the initiation of cytokine and chemokine expression within the joint before the onset of arthritis, whereas the expression of FcgammaRI and or FcgammaRIII controlled cytokine and chemokine expression late in the development of PGIA during the onset of disease. These results suggest that FcgammaRs are critical for the development of inflammation during PGIA, possibly by maintaining or enhancing inflammatory cytokine and beta-chemokine production.