IL17A and rheumatoid arthritis: In the occurrence and development of RA, the role of Th17/IL-17 is also controversial.211 Hot et al.212 found that IL-17 isoform IL-17A can induce three signaling pathways of MAPK family ERK, p38, and JNK and downregulate transcription factors p65 NF-κB and AP-1.