Cathepsin B and its endogenous inhibitor cystatin C in rheumatoid arthritis synovium

Objective. To compare the expression of cathepsin B and its endogenous inhi bitor cystatin C in synovial tissue of patients with rheumatoid arthritis ( RA) and to determine the cell type expressing cystatin C. Methods. The expression of cathepsin B and cystatin C was studied by immuno histochemistry in synovial tissue of 10 patients with RA and compared to he althy controls. Applying double labeling methods, the expression of catheps in B was compared to that of cystatin C. To determine the cell type express ing cystatin C, double labeling with anti-CD68 (PG-M1) was performed. Results. Both cystatin C and cathepsin B were strongly expressed, in synovi ocytes of patients with RA. Furthermore, fibroproliferative tissue at the: site of cartilage and bone destruction contained fibroblast-like and macrop hage-like cells positive for cystatin C and cathepsin B, whereas normal syn ovial tissue exhibited only limited expression of these molecules. Osteocla sts revealed positive staining for CD68 and cystatin C, but not for catheps in B. Conclusion. Cystatin C is a product of both macrophage-like and fibroblast- like synoviocytes. The strong expression of both the matrix degrading cyste ine proteinase cathepsin B and the cysteine proteinase inhibitor cystatin C in rheumatoid synovium, particularly at the sites of bone and cartilage er osion, suggests that cystatin C - although increased - is not sufficient to prevent matrix degradation by cathepsin B.