IL17A and rheumatoid arthritis: IL-23 is known to promote IL-17 production [49] and was detected in RA synovial fibroblasts, but, like a loop, it can be upregulated by IL-17 in RA synovial fibroblasts via PI3-kinase/Akt-, NF-κB-, and p38-MAPK-mediated pathways [50].