MAPK8 and rheumatoid arthritis: JNK and ERK1/2 MAPKs are closely associated with collagenase production and inflammatory responses of fibroblast-like synoviocytes (RAFLS), whereas p38 MAPK isoforms is involved in regulating many of cellular biological processes, concretely synovial inflammatory cytokine production, which participate to the RA pathogenesis [45].