Electron microscopy and immunolabeling of Yersinia antigens in human synovial fluid cells

Recent findings have emphasized the involvement of bacterial antigens in synovitis in reactive arthritis. It is still unclear, however, in what form the microbial material exists in the joint. Both antigen-containing cells and intact bacteria have been proposed as candidates on the basis of immunohistochemical studies of the synovial membrane. This study addresses that question by electron microscopy and peroxidase immunolabeling of synovial fluid cells from three patients with reactive arthritis triggered by Yersinia enterocolitica O:3. For all three patients a diffuse reaction in the cytoplasm of phagocytes was interpreted as bacterial material in a degraded form. These results are consistent with our proposal that intact bacteria rarely, if ever, enter the joints of Yersinia-triggered reactive arthritis patients.