Structure and function of the T3/T cell receptor complex.

The T3/T cell receptor 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, alpha and beta chains are distinct), the gamma, delta and epsilon chains are invariant between human 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 three 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 or target cell and an activating signal is transduced to the cytoplasmatic side of the plasma membrane via the T3 complex. Thus, T cell responses are initiated immediately upon binding of ligand. In our model, Ca+2 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.