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Immune synovitis in rabbits. Effects of differing schedules for intra-articular challenge with antigen.

The effects of varying intra-articular (ia) doses of bovine serum albumin (BSA) antigen on immune synovitis in rabbits have been investigated. Chronic synovitis, characterized by mononuclear cell infiltration in synovial tissues, was induced by a single ia challenge with BSA in sensitized rabbits. However, cartilage and bone erosions and pannus formation were rarely observed. By varying the number and magnitude of the BSA challenges, lesions with different characteristics were observed at different times of analysis of joint pathology. In 3- to 10-week studies, multiple ia challenges with BSA produced lesions characterized by severe cartilage and bone changes; polymorphonuclear leukocyte (PMN) exudates; and mononuclear cells and, sometimes, PMNs in synovial tissues. Substantial increases in knee widths and synovial tissue weights also observed. By increasing the frequency of ia injections, more severe changes were produced more rapidly, so that within a 3-week period, the animals also experienced pain and were unable to fully extend their antigen-challenged knees. Some of the lesions observed in immune synovis resembled those in rheumatoid arthritis (RA). However, the presence of large numbers of PMNs in synovial tissue under certain conditions suggests some possible differences between the pathogenesis of experimental synovitis and RA.