Small GTPases in lymphocyte biology - Rho proteins take center stage

Almost a decade ago, the small GTPase Ras was shown to be activated in resp onse to antigen receptor triggering in T cells. Since then, Ras has been fu rther characterized as a central molecule for the regulation of signal tran sduction pathways in lymphocytes. However, over the last couple of years, i ts exclusive role in lymphocyte biology has been challenged by the emergenc e of its relatives of the Rho family. Today it is well established that Rho GTPases act as unique molecular switches at several critical checkpoints i n lymphocyte development and function. Additionally, a new and critical con cept in GTPase signaling has taken shape over the last couple of years in t hat small GTPases are able to regulate quite diverse cellular processes in the immune response by linking to multiple bio-chemical effector pathways.