In line with our mRNA data, immunoreactive cells for PGE2- (13-fold) and its processing enzymes COX-2- (9-fold) and mPGES-1- (2.4-fold) were highest in the synovial tissue of RA patients compared to controls, followed by synovial tissue of OA patients (9-fold, 7-fold, and 2.6-fold, respectively) and of JT patients (5.8-fold, 7.5-fold, and 2-fold, respectively). This evidence concerns the gene PTGS2 and rheumatoid arthritis.