Receptors for immunoglobulin (Ig)G (FcγRs) are important for the antibody-mediated effector functions of the immune system. FcγRI and FcγRIII trigger cell activation through a common γ chain, whereas FcγRII acts as a negative regulator of antibody production and immune complex–triggered activation. Here we describe the in vivo consequences of FcγR deficiency in a mouse model of human rheumatoid arthritis. FcRγ chain–deficient mice on arthritis-susceptible DBA/1 background were immunized with collagen for induction of collagen-induced arthritis. The DBA/1 mice lacking FcRγ chain were protected from collagen-induced arthritis in contrast to wild-type mice, although both groups produced similar levels of IgG anticollagen antibodies. In comparison, DBA/1 mice lacking FcγRII developed an augmented IgG anticollagen response and arthritis. These observations suggest a crucial role of FcγRI and FcγRIII in triggering autoimmune arthritis.

IgG anti-collagen type II (CII) antibodies (Ab) can induce arthritis in healthy mice. Here we have investigated if single monoclonal IgG anti-CII Ab can induce arthritis in CIA-susceptible DBA/1 mice and if there is an IgG subclass dependency. The involvement of Fc receptors for IgG (Fc + R) in anti-CII Ab-mediated arthritis was also investigated by comparing the clinical outcome in DBA/1 mice to those in Fc + R-deficient mice. We demonstrate for the first time that single mAb to naive DBA/1 mice can induce persistent arthritis. Histology of the inflamed joints revealed massive cellular infiltrate and cartilage and bone destruction. All IgG subclasses tested (IgG1, IgG2a and IgG2b) were arthritogenic, with the IgG1 and IgG2b isotypes as the dominating arthritogenic Ab. Pathogenicity was dependent on engagement of activating Fc + R, as FcR + -deficient mice were completely resistant to Ab-mediated arthritis. The arthritis induced with the IgG1 and IgG2b Ab was also inhibited by Fc + RIII disruption, whereas arthritis mediated by the IgG2a Ab was not substantially affected. The arthritic response of the IgG1 and IgG2b isotypes, but not of the IgG2a Ab, was further enhanced in mice lacking the inhibitory Fc + RIIB. These results demonstrate that single IgG anti-CII mAb can induce erosive arthritis and that IgG anti-CII Ab mediate arthritis by engagement of Fc + R.

Collagen-induced arthritis (CIA) is an experimental animal model of human rheumatoid arthritis being characterized by synovitis and progressive destruction of cartilage and bone. CIA is induced by injection of heterologous or homologous collagen type II in a susceptible murine strain. DBA/1J mice deficient of complement factors C3 (C3−/−) and factor B (FB−/−) were generated to elucidate the role of the complement system in CIA. When immunized with bovine collagen type II emulsified in CFA, control mice developed severe arthritis and high CII-specific IgG Ab titers. In contrast, the C3−/− and FB−/− were highly resistant to CIA and displayed decreased CII-specific IgG Ab response. A repeated bovine collagen type II exposure 3 wk after the initial immunization led to an increase in the Ab response in all mice and triggered arthritis also in the complement-deficient mice. Although the arthritic score of the C3−/− mice was low, the arthritis in FB−/− mice ranked intermediate with regard to C3−/− and control mice. We conclude that complement activation by both the classical and the alternative pathway plays a deleterious role in CIA.

An intradermal injection of Freund's incomplete adjuvant oil (FIA) without further additives was shown to induce erosive polyarthritis in dark Agouti (DA) rats, but not in Lewis rats. Histological examination revealed joint inflammation, first with polymorphonuclear cells and synovial hyperplasia, and subsequently, with multinucleated giant cells. Both constituents of FIA, mineral oil and Arlacel A, as well as Pristane oil were arthritogenic, whereas vegetable oil were not. Re-administration of adjuvant oil after recovery failed to induce arthritis, thus making possible a role of specific immunity in this new form of arthritis in rats.

Multiple sclerosis (MS) is simulated by various forms of experimental autoimmune encephalomyelitis, in which T cells, antibodies, cytokines and complementary factors interact with the central nervous system (CNS) myelin proteins and lead to inflammatory damage. We investigated the role of Fc receptors (FcRs), which link the cellular and humoral branches of the immune system, in myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE), using two different FcRg knockout DBA/1 mice. The first knockout were the FcRg chain-deficient mice, which lack FcgRI, FcgRIII and FceRI, while the second knockout mice lack only FcgRII. The lack of FcgRII enhanced the disease susceptibility with associated increased CNS demyelination. While FcRg / DBA/1 mice also developed pronounced CNS infiltration and myelin destruction, FcRg ±/± littermates were protected despite initial peripheral autoimmune responses to MOG. In vitro analyses revealed equivalent potentials of fluid phase phagocytosis of myelin and MOG in bone-marrow macrophages derived from both FcRg / and FcRg ±/± mice, while MOG-immunoglobulin (Ig)G immune complexes were only internalized by FcRg / macrophages. This was associated with cellular activation in FcRg / but not FcRg ±/± macrophages, as assessed by the activation of intracellular mitogen activated protein (MAP)-kinase signalling elements. We propose that protection from EAE in FcRg-deficient mice is due to the inefficient antigen processing/presentation of myelin proteins during the induction of secondary immune responses locally in the CNS, which leads to demyelination. This demonstrates the importance of FcR in the promotion of autoimmune inflammation of the CNS and highlights the therapeutic possibility of treatment of MS with FcR-directed modalities.