In vitro responses to a 65-kilodalton mycobacterial protein by synovial T cells from inflammatory arthritis patients.

Bacterial Ag, especially those of mycobacteria, have been implicated in the pathogenesis of experimental inflammatory arthritis in rodents, while in man, reactive arthritis has a clear temporal relationship to infection with particular bacteria. To investigate the role of immune responses to bacterial Ag in inflammatory arthritis, we have examined the proliferative responses of paired synovial fluid and PBMC when stimulated with 1) suspensions of irradiated or heat-killed bacteria associated with reactive arthritis (ReA), 2) purified protein derivative, 3) a recombinant 65-kDa heat shock protein of Mycobacterium leprae. The 65-kDa Ag was stimulatory to synovial fluid mononuclear cells, but not PBMC, from patients with different arthropathies, including most of those with ReA, but also some with rheumatoid arthritis. Furthermore, the magnitude of these responses correlated more closely with responses to ReA-associated bacteria (such as Salmonella), than with responses to the mycobacterial Ag represented in purified protein derivative. These results suggest that the 65-kDa molecule, which is common to a wide range of bacteria, may be an important immunogen for the T cell-mediated immune responses within the joint in different clinically defined inflammatory arthropathies.