FPR2 and rheumatoid arthritis: Based on the finding that scolopendrasin IX acts on FPR2 and the peptides show anti-arthritic effects in the K/BxN serum transfer model, we investigated the role of FPR2 in mediating the therapeutic activity of the peptide against RA using an FPR2-selective antagonist, WRWWWW (WRW4)19.