OBJECTIVE To determine the impact of type II collagen (CII)-reactive T cells on the production of chemokines in the joints of patients with rheumatoid arthritis (RA). METHODS T cell proliferative responses to bovine CII were assayed in synovial fluid (SF) mononuclear cells and peripheral blood mononuclear cells. CII-stimulated T cells were cocultured with fibroblast-like synoviocytes (FLS). The expression of interleukin-8 (IL-8), monocyte chemoattractant protein 1 (MCP-1), and macrophage inflammatory protein 1 alpha (MIP-1 alpha) in the sera, SF, and supernatant of the CII-stimulated T cells and FLS coculture was measured by enzyme-linked immunosorbent assays. RESULTS The levels of IL-8, MCP-1, and MIP-1 alpha in SF were significantly higher than those in paired sera of RA patients. IL-8, MCP-1, and MIP-1 alpha levels in SF were strongly correlated with T cell responses to CII. When FLS were cocultured with CII-stimulated T cells, the production of IL-8, MCP-1, and MIP-1 alpha was significantly increased. This increase correlated well with the T cell proliferative response to CII. Chemokine production by coculture of CII-stimulated T cells and FLS was mediated mainly by direct cell-cell contact through CD40 ligand-CD40 engagement. CONCLUSIONS Our data indicate that the presence of CII-reactive T cells in RA joints can increase the production of chemokines such as IL-8, MCP-1, and MIP-1 alpha through interaction with FLS. This chemokine production is mediated by cell-cell contact, including CD40 ligand-CD40 engagement. These results suggest that CII-reactive T cells play a crucial role in the amplification and perpetuation of the inflammatory process in the rheumatoid synovium.