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 degradi ng proteinase cathepsin B and its endogenous inhibitor cystatin C in rheuma toid arthritis (RA) with special regard to multinucleated synovial giant ce lls (SGC). We applied an immunohistoehemical double-labeling technique. SGC strongly expressed cystatin C and CD68, but were negative for cathepsin B. This staining pattern occured in osteoclasts as well. Our findings support the idea that in RA matrix destruction by cathepsin B is not mediated by S GC or osteoclasts, but by mononuclear synoviocytes.