MAPK8 and rheumatoid arthritis: In contrast to previous studies that have found Th17/Tregs imbalance and STAT activation as the key mechanism in IL-6 associated RA immunopathology [19,20,21], we found that MAPK family members (ERK1/2, p38 MAPK and JNK1/2) are the major signaling pathways after PMs exposure.