Responses of synovial fluid and peripheral blood mononuclear cells to bacterial antigens and autologous antigen presenting cells.

The specificity of T cells in the inflamed joints of patients with rheumatoid arthritis (RA) has been the subject of much study. Bacterial antigens are suspect in the aetiology of rheumatic diseases. The responsiveness of the mononuclear cell fraction of peripheral blood and synovial fluid of patients with RA and of patients with rheumatic diseases other than RA to bacterial antigens such as cell wall fragments of the anaerobic intestinal flora, cell wall fragments of Streptococcus pyogenes, intestinal flora derived peptidoglycan polysaccharide complexes, the 65 kilodalton protein of Mycobacterium tuberculosis, and muramyldipeptide was investigated. No significant difference in response was found to all these bacterial antigens in the synovial fluid of patients with RA compared with the responses in patients with other rheumatic diseases. The highest responsiveness in the synovial fluid of the patients with RA was to the streptococcal cell wall fragments and to the 65 kilodalton protein. Higher responses to several bacterial antigens in the synovial fluid of patients with RA were found compared with peripheral blood from the same patient group. The antigen presenting cell population of the synovial fluid in patients with RA and the patients with other rheumatic diseases was found to be stimulatory for autologous peripheral blood T cells even in the absence of antigen. This suggests an important role for the synovial antigen presenting cell in the aetiology of inflammatory joint diseases.