PTGS2 and rheumatoid arthritis: When extending this work by scanning two participants with rheumatoid arthritis and two healthy controls, we identified localized infiltration of leukocytes into the synovial membrane, a classic pathological finding in rheumatoid arthritis [36, 37] that has also been associated with high expression of COX-2 and TSPO [16, 27, 38, 39].