Immunologic reactions of rabbit anti-Mycoplasma arthritidis serum with in vitro cultivated rat synovial cells.

The pathogenesis of the intra-articular, arthritic-inflammatory reaction caused by Mycoplasma arthritidis in susceptible rats and mice is poorly understood. To investigate this problem, synovial cells from normal Sprague-Dawley rats were cultured and studied in vitro. These cells continued to produce hyaluronic acid as measured by viscosity and chemical assays. Normal synovial cells were treated with rabbit serum specimens taken before and after immunization with M. arthritidis. Cytotoxicity assays indicated that the cells were killed in the presence of rabbit anti-M. arthritidis serum but not with preimmunization serum specimens. The anti-M. arthritidis serum was not cytotoxic to monolayer cultures of HEp-2, Vero, or L-cells. Antiserum produced in response to M. fermentans, M. hominis, and M. pulmonis did not produce a cytotoxic effect on the cultured synovial cells. From immunofluorescence studies it was demonstrated that the interactions occurred between the rabbit anti-M. arthritidis serum and synovial cell surface antigens. Extreme precautions were taken to prevent mycoplasmal contamination of rats and the synovial cells in culture. These observations would appear to support previous reports implicating mycoplasmas as biological triggering mechanisms of autoimmune reactions.