DETECTION OF COX-1 AND COX-2 ISOFORMS IN SYNOVIAL-FLUID CELLS FROM INFLAMMATORY JOINT DISEASES

Objective. To investigate the expression of cyclooxygenase-1 (COX-1) a nd cyclooxygenase-2 (COX-2) in cells from synovial fluid (SF) of patie nts with acute or chronic arthritis. Methods. SF was obtained from eig ht patients with acute crystal-induced arthritis, nine with rheumatoid arthritis and four with psoriatic arthritis. COX-1 and COX-2 gene exp ression was studied by reverse transcriptase-polymerase chain reaction (RT-PCR). Protein expression was detected by Western blotting and imm unocytochemistry. Results. There was expression of COX-1 mRNA in all a nd COX-2 mRNA in most of the SF samples from acute or chronic arthriti s. By immunocytochemistry, both COX-1 and COX-2 immunoreactivity was r estricted to a variable fraction of mononuclear cells. COX-1 staining was observed in 10-fold more cells than COX-2. By Western blotting, CO X-1 protein was detected in 60% of the SF samples and COX-2 in none. T here were no differences in the pattern of COX-1 and COX-2 expression between chronic and acute SF samples. Conclusion. In arthritis, both C OX-1 and COX-2 isoforms are expressed by SF cells. COX-1 is the most a bundant isoform. Since the strong COX-1 immunostaining observed in a f raction of mononuclear SF cells is not observed in peripheral blood le ucocytes, it may be the result of either the activation or recruitment of a subset of mononuclear cells with a high COX-1 expression level.