Serum levels of soluble CD44 variant isoforms are elevated in rheumatoid arthritis.

Serum levels of soluble CD44 variant proteins including sequences encoded by exon v5 and exon v6 (sCD44v5, sCD44v6) were determined in patients with inflammatory rheumatic diseases: 56 with rheumatoid arthritis (RA+) and 31 with miscellaneous inflammatory rheumatic diseases (MIRD). There were very significantly higher serum levels of sCD44v5 and sCD44v6 in patients with RA+ than in those with MIRD (RA+ to MIRD: sCD44v5: 81 +/- 54 ng/ml to 33 +/- 13 ng/ml; sCD44v6: 237 +/- 124 ng/ml to 166 +/- 53 ng/ml; both P << 0.001). In RA+ elevated serum levels of sCD44v5 were correlated with the inflammatory activity of disease. In 17 patients with RA+ three or four follow-up measurements of sCD44v5 were performed within 6 months. The development of sCD44v5 serum levels reflected the clinical course of disease in the patients investigated.