TNFSF11 and rheumatoid arthritis: In addition, Fc-receptor-like 4 (FcRL4)+ B cells, a unique B-cell subset observed in RA synovium but not in the peripheral blood (PB), are proposed as potent effectors expressing RANKL at high levels, although the impact of RANKL+ B cells on osteoclastogenesis has yet to be clarified [14].