As Sema4A expression is also elevated in other CD4+ T cell-mediated diseases including, asthma, RA and MS [11,12,19,24], it is tempting to speculate that Sema4A-PlexinD1 signaling is involved in the dysregulation of Th cell homeostasis observed in these diseases and targeting this axis might be a beneficial therapeutic approach. Here, CD4 is linked to rheumatoid arthritis.