PTGER1 and rheumatoid arthritis: We, therefore, systemically investigated the distribution, localization and abundance of PGE-2, its processing enzymes COX-2, and mPGES-1, as well as its corresponding prostanoid receptor subtypes EP1-4 within the synovium of patients with joint trauma (JT), osteoarthritis (OA), and rheumatoid arthritis (RA).