This study systematically investigated potential differences in the abundance of PGE-2, its processing enzymes COX-2 and mPGES-1, and its corresponding prostanoid receptor subtypes EP1-4 within the synovial tissue of JT, OA, and RA patients in direct comparison to each other and to controls who simply underwent a diagnostic arthroscopy. Here, PTGER1 is linked to rheumatoid arthritis.