Progression of articular destruction and the production of tumour necrosis factor-α in antigen-induced arthritis in rabbits

We examined the progression of articular destruction and the production of tumour necrosis factor-alpha (TNF-alpha) in antigen-induced arthritis (AIA) in rabbits, i.e. flare-ups of inflammation induced by repeated intra-articular injections (single, twice and three times) of antigen. A marked progression of articular destruction and an infiltration of inflammatory cells in the synovium were observed with the increase in the number of antigen injections. An immunohistochemical analysis of the synovial lesions following three injections of antigen revealed that the lymphoid follicles consisted mainly of CD4(+) T cells and IgG/IgM(+) B cells. There were marked infiltrations of IgG(+) plasma cells around the lymphoid follicles. In contrast, the production of TNF-alpha in the synovial fluid and the erythrocyte sedimentation rate (ESR), which is a marker of systemic inflammatory activity in rheumatoid arthritis, peaked at 6 h and 24 h, respectively, following the last injection of antigen. These values were also greater following the repeated injections of antigen compared with the single injection. The TNF-alpha was produced markedly in the joints at the onset of the flare-ups of arthritis following the repeated injections of antigen, and the elevation of the ESR and an acceleration of the inflammatory response in the synovium were observed with a concomitant progression of severe articular destruction, suggesting that the marked production of TNF-alpha at the time of flare-ups may be involved in the exacerbation of AIA in rabbits.