Expression of CD44 in normal and rheumatoid synovium and cultured synovial fibroblasts.

OBJECTIVE To determine if expression of CD44, the principal receptor for hyaluronan, was altered in rheumatoid (RA) synovium and cultured rheumatoid synovial fibroblasts. METHODS Synovium was obtained from normal adult human joints (n = 4) and from joints of patients with RA (n = 5). Specific monoclonal antibodies to CD44 were used in immunofluorescence of whole synovium and cultured synovial fibroblasts and in quantitative Western blotting and ELISA of CD44 in cultured synovial fibroblasts. RESULTS CD44 was restricted to the lining layer in normal synovium but present, in reduced concentrations, throughout rheumatoid synovium. Cultured rheumatoid cells were 19% larger in area and showed far fewer and less extensive CD44-positive cytoplasmic extensions, together with reduced staining intensity compared with normal. Quantitative Western blotting normalised for cell protein showed a 75% reduction (normal = 1754 (835), rheumatoid = 409 (84) mean (SD) arbitrary units) in the amount of CD44 in rheumatoid cells compared with normal, and enzyme linked immunosorbent assay (ELISA) of cultured cell monolayers normalised for cell number indicated a 29% reduction (normal = 0.707 (0.110), rheumatoid = 0.504 (0.103), mean (SD) optical density at 405 nm). CONCLUSIONS Rheumatoid synovial cells showed altered morphology and reduced CD44 expression compared with normal cells. CD44, by means of modulated associations with the cytoskeleton, may be involved in cell shape change.