BSG and rheumatoid arthritis: Based on the reports that CD147 is a high affinity receptor for CyPA and responsible for a cyclophilin signaling cascade that culminates in extracellular signal-regulated kinase (ERK) activation and chemotaxis [20,21], we examined the chemoattraction of CyPA for peripheral mononuclear cells in RA and the blockage effect of anti-CD147 antibody and AP9 on this.