New models of chronic synovitis in rabbits induced by mycoplasmas: microbiological, histopathological, and immunological observations on rabbits injected with Mycoplasma arthritidis and Mycoplasma pulmonis

Abstract

A dose-dependent chronic synovitis was induced in rabbit knees after the intra-articular injection of both Mycoplasma arthritidis and Mycoplasma pulmonis. The inflammation progressed from an initial acute phase at 1 week characterized by edema, infiltration of the synovium with monocytes and heterophils, and desquamation of lining cells, to a more chronic phase at 1 and 3 mths in which villus hyperplasia, lymph 'nodules', mononuclear cell infiltration, fibroplasia, and collagen deposition were prominent. With one exception, mycoplasmas could no longer be cultivated from the joints 1 mth postinoculation. Both mycoplasma species evoked a humoral antibody response which was more marked in synovial fluids than in peripheral blood. A cell-mediated immune reaction, as evidence by an enhanced uptake by [3H]thymidine by sensitized blood, spleen, or node lymphocytes in the presence of homologous antigen, was detected only in rabbits injected wtth M. pulmonis. Lymphocytes taken from arthritic rabbits were no more cytotoxic toward synovial cells derived from normal or arthritic rabbits than were normal lymphocytes. The models of synovitis used offer a convenient probe for determining the mechanisms of mycoplasma-induced inflammation, since they require only a single injection of the initiating agent, and, in addition, utilize an animal host large enough for detailed investigation into the nature of mycoplasma/synovium interactions.