Double immunofluorescence confocal microscopy showed that prostanoid receptor subtypes EP2 and EP3 were mainly expressed in CD15-IR granulocytes of JT synovium (e.g., Figure S2) and predominantly identified in CD68-IR macrophages and P4HB-IR fibroblasts of OA (e.g., Figure S3) and RA synovium, whereas they were seen to a large extent in Ab-1 plasma cells only in RA synovium (e.g., Figure S4). The gene discussed is PTGER3; the disease is rheumatoid arthritis.