Cathepsin B in synovial cells at the site of joint destruction in rheumatoid arthritis.

Based on the concept that proteolytic enzymes, like cathepsins, are associated with tissue destruction, we investigated the expression of the matrix-degrading cysteine proteinase cathepsin B in synovial tissues from the joints of patients with rheumatoid arthritis. The data indicate an enhanced transcription of cathepsin B in synovial cells when compared with normal fibroblasts, cathepsin B-producing epithelial tumor cells (SW1116), or fibroblasts derived from inflamed tonsils. Immunolocalization of cathepsin B appeared to be restricted mainly to the synovial cells attached to cartilage and bone at sites of rheumatoid joint erosion.