A molecular basis for thymic selection: regulation of T11 induced thymocyte expansion by the T3-Ti antigen/MHC receptor pathway.

T-cell activation is mediated through either the T3-Ti molecular complex or the TII sheep erythrocyte bindingglycoprotein. The former represents the nominal antigen/MHC receptor whereas the latter is a surface component of an alternative pathway which appears much earlier in intrathymic differentiation. Recent studies indicate that the T3-Ti complex regulates the TII activation pathway. Here, taking account of the ontogeny and physiology of this pathway, Ellis Reinherz offers a simple model to account for the selection in thymus against T cells with high-affinity, potentially autoreactive antigen receptors.