Synovial giant cells in rheumatoid arthritis: expression of cystatin C, but not of cathepsin B.

This study was designed to investigate the expression of the matrix degrading proteinase cathepsin B and its endogenous inhibitor cystatin C in rheumatoid arthritis (RA) with special regard to multinucleated synovial giant cells (SGC). We applied an immunohistochemical double-labeling technique. SGC strongly expressed cystatin C and CD68, but were negative for cathepsin B. This staining pattern occurred in osteoclasts as well. Our findings support the idea that in RA matrix destruction by cathepsin B is not mediated by SGC or osteoclasts, but by mononuclear synoviocytes.