Pathogenesis of acute arthritis due to viable Chlamydia trachomatis (mouse pneumonitis agent) in C57Bl/6 mice

The purpose of this investigation was to determine the natural history and pathogenesis of the acute arthritis induced by inoculation of a viable Chlamydia trachomatis biovar (mouse pneumonitis agent or MoPn) in C57Bl/6 mice. Immunologically naive (previously unsensitized) mice as well as mice immunized against Chlamydia (MoPn) by vaginal infection were employed. Both intravenous and intraarticular inoculations were employed. No arthritis developed after intravenous injections of MoPn although statistically significant antibody titers and splenic enlargement ensued. Intra-articular inoculation into knee joints produced a definite arthritis of 7 to 10 days duration marked by granulocyte and mononuclear cell infiltration of the joint and vacuolated synovial macrophages that stained heavily for chlamydial antigen by immunoperoxidase technique. Statistically significant increases in articular acute and chronic inflammation (P less than 0.02 were observed in previously sensitized, but not unsensitized, female mice at 2 but not 7 days after intra-articular chlamydial challenge. Chlamydiae were isolated from injected joints up to day 5, but not at day 10, after challenge. Chlamydial antigen disappeared rapidly from knee joints between day 10 and 15 after challenge. Electron micrographs demonstrated vacuolated synovial cells of the macrophage type, many of which contained degenerating chlamydial elementary bodies. Reticulate and intermediate bodies also were seen but were far less frequent than degenerating elementary bodies. Unaltered elementary bodies were difficult to identify beyond day 2 after articular inoculation. Thus, it appears likely that intra-articular chlamydial survival is shorter than the duration of the arthropathy. This may have important implications in attempts to identify chlamydiae in human joints in Reiter's Disease.