The T-cell receptor/T3 complex.

The T-cell receptor/T3 complex is a protein ensemble inserted in the plasma membrane of human thymus-derived lymphocytes. Whereas the alpha and beta chains are variable elements (i.e. between different T-cell clones, the alpha and beta chains are variable elements (i.e. between different T-cell clones, the alpha and beta chains are related but distinct), the gamma, delta and epsilon chains are invariant between T-cell clones. Recently, genes coding for the alpha, beta and delta chains have been isolated. Functional studies in several laboratories, including our own, suggest a 'division of labor' between the alpha/beta-chain heterodimer (T-cell receptor) and the 3 other polypeptide chains (T3-gamma, -delta, -epsilon): the T-cell receptor alpha and beta chains together recognize antigen and MHC product on the antigen-presenting target cell and an activation signal is transduced to the cytoplasmic side of the plasma membrane via the T3 complex. Thus T-cell responses are initiated immediately upon binding of ligand. In our model, Ca2+ influx plays a pivotal role in the signal-transducing event. In fact, we postulate that the T3-epsilon chain itself might be a calcium gate.