Hypothesis: cartilage catabolic cofactors in human arthritis.

Cartilage degradation in rheumatoid arthritis (RA) and osteoarthritis (OA) is commonly thought to be mediated by interleukin 1 (IL-1) and tumor necrosis factor (TNF). However, recent new evidence suggests that IL-1 and TNF on their own do not mediate all the cartilage changes seen in RA and OA. We propose that cartilage degradation is mediated by a complex network of cytokines, including IL-1, TNF and at least one cofactor present in synovial fluid.