Moreover, it has been suggested that prostaglandin E2 (PGE2) stimulation, independently of IL-23, can trigger IL-17A production in RA synovial fibroblasts (47), but several studies in mice indicated that PGE2 does need IL-23 signaling for stimulation of IL-17A production (48–50). This evidence concerns the gene IL37 and rheumatoid arthritis.