[Pathogenesis of spontaneous chronic polyarthritis in MRL mice]

In a sequential study the pathogenesis of chronic polyarthritis occurring spontaneously in MRL mice was analysed by light microscopy. A total of 128 MRL mice of both substrains (MRL/Mp-lpr/lpr and +/+) and different age groups was studied. In 50 lpr/lpr mice, tinctorial and histochemical methods were applied for the identification of fibrin/fibrinoid, iron compounds, amyloid, and proteoglycan. The earliest lesions seen in mice of substrain lpr/lpr at the age of 2 months were proliferation of synovial lining cells and loss of tinctorially demonstrable proteoglycan in the articular cartilage. Beginning at 3 months, severe joint destruction associated with pannus formation was encountered usually in knee, carpal and tarsal joints. Besides inflammatory processes in tendons, nerves and musculature fibrinoid-necrotising panarteritis occurred in the intra- and extraarticular tissue. Furthermore, fibrin-containing exudations and deposits of fibrinoid material, occurred in the synovium of large joints and in the periarticular connective tissue of phalangeal joints. The occurrence of these morphological changes, destructive arthritis, vasculitis and periarticular inflammatory changes, was, at the age of 3 months, associated with a highly significant increase of circulating immune complexes. In mice of substrain +/+ aged 1 year and older, arthritic changes with synovial lining cell proliferation, cartilage destruction and inflammatory periarticular lesions developed.