Evidence for preferential T cell receptor V beta gene usage and T cell clonal expansion in the synovium of BB rats with early-onset collagen-induced arthritis

The roles of interleukin-18 in collagen-induced arthritis in the BB rat

Interleukin (IL)-18 is a member of the IL-1 cytokine family. Its expression is increased in rheumatoid arthritis synovium, and its proinflammatory effects have been demonstrated in experimental models of murine arthritis. Here, we investigate the actions of varying doses of recombinant rat IL-18 (rIL-18) on the course of type II collagen-induced arthritis (CIA) in BB rats, including clinical and immune events, plus splenic cytokine production. Small doses of rIL-18 (10 and 50 microg/rat) administered intraperitoneally (i.p.) increased arthritis incidence and severity (P < 0.01) when a low-potency CII preparation was used for immunization. IgG1 and IgG2a anti-CII antibody levels were significantly greater in rats given 10 and 50 microg rIL-18 doses than controls. rIL-18 significantly increased levels of proinflammatory cytokines [interferon (IFN)-gamma, IL-2, tumour necrosis factor (TNF)-alpha and IL-6] produced by splenocyte cultures. Larger doses of rIL-18 (300 microg/rat) suppressed arthritis and immunity. To ascertain whether the pro-arthritic effects of IL-18 could be attenuated, rats were treated with neutralizing rabbit anti-rIL-18 IgG before immunization with a high-potency CII preparation. When given serially for 3 weeks, the incidence and severity of CIA, in addition to anti-CII IgG2a and splenic IL-6 and IFN-gamma production, were all significantly reduced. Similar results were noted when antibody was given twice, just before arthritis onset. These results demonstrate that IL-18 plays an important proinflammatory role in the pathogenesis of CIA which is achieved, in part, by an immunostimulatory action. Neutralizing endogenous IL-18 with antibodies attenuated CIA, CII immunity and cytokine responses. These studies support the use of IL-18 antagonists as treatments for inflammatory arthritis.

Autoreactivity in collagen-induced arthritis of rats: a potential role for T cell responses to self MHC peptides

Collagen-induced arthritis (CIA) is a chronic inflammatory arthropathy of rats which follows immunization with bovine type II collagen (bCII). T cell lines generated from arthritic rats have been shown to be self-reactive and proliferate in an autologous MLR, which is MHC-dependent. However, the peptides which drive this autoreactive response remain to be elucidated. T cell lines, generated initially to bCII, were cultured with synthetic peptides representing potential autoreactive self epitopes. C1q-c(50-64) peptide, which demonstrates sequence homology to the bCII(184-198) peptide, failed to stimulate T cell proliferation suggesting that the autologous MLR was not due to antigen cross-reactivity with this self peptide. In contrast, several peptides from the amino-terminal region of the RT1D(u) MHC class II molecule stimulated proliferative responses. These results suggest that immunization with bCII leads to activation of a population of autoreactive T cells which respond in an autologous MLR, and that this response could be due, in part, to T cell reactivity to self MHC peptides.

Antigen presentation of Type II collagen in rats

Collagen-induced arthritis (CIA) is a T-cell dependent disease of rats which follows immunization with bovine type II collagen (bCII). Susceptibility to CIA is linked to the genes encoding the major histocompatibility complex (MHC), suggesting that antigen presentation is important in disease pathogenesis. Antigen-presenting cells (APC) (macrophages, dendritic cells (DC) and B cells) were prepared from WA/KIR/KCL rats and presentation of antigen, in the form of native protein (bCII) or synthetic peptide (bCII:184-198), was assessed in T-cell proliferation assays. Whilst macrophages inhibited proliferative responses to bCII, splenic or thymic low density cells, enriched for DC, presented both bCII and bCII(184-198) peptide. However, bone marrow-derived DC, which stimulated T-cell responses to OVA, failed to present bCII, suggesting differences in processing of these two antigens. B-cell depletion from lymph node cells abrogated the proliferative response to bCII and reconstitution of a T-cell population with B cells restored the proliferative response, indicating that B cells are important for stimulating T-cell responses to bCII. B cells play a critical role in CIA by producing pathogenic anti-bCII antibodies, and we propose that B cells are also important APC which present bCII to CD4+ T cells.