Compared with JNK and extracellular signal-regulated kinase (ERK), p38 MAPK is strongly activated by IL-1β stimulation, and is highly susceptible to PIP-18 inhibition, suggesting that the effect of peptide on MMP transcription is related to its ability to modulate the activation of the p38 MAPK pathway in RA SF cells. Here, MAPK8 is linked to rheumatoid arthritis.