Type II collagen induced arthritis: comparison of histological changes in arthritis-susceptible and...

Wistar rats (type II collagen-induced arthritis-susceptible) and PVG.RT1u rats (arthritis-resistant) were immunised with type II collagen and histological changes in the synovial tissues of the hind feet and in the popliteal lymph nodes draining these feet were examined and compared with unimmunised rats. There were no apparent differences in the joints of unimmunised rats of each strain, but the popliteal lymph nodes of the Wistar rats appeared more "activated", suggesting possible differences between strains in the continuous, low-grade release of antigens from the joints. Whilst the joints of arthritic rats showed the most marked histological changes, the joints of immunised PVG.RT1u rats and of non-arthritic Wistar rats showed some minor changes in the synovia and loss of cartilage with a concomitant increase in the size of the popliteal lymph nodes. The number of mast cells per unit area increased in the lymph nodes of immunised PVG.RT1u rats in proportion to the size increase, but decreased in those draining arthritic Wistar rat feet. The number of mast cells per unit area of synovium decreased most in arthritic feet and the staining pattern of the mast cells altered in the most severely arthritic feet, suggesting a change in mast cell population. These differences in mast cells may be directly related to whether or not clinical arthritis develops in a particular joint. Further study of mast cell sub-populations is warranted.