[The T-lymphocyte antigen receptor]

The precise knowledge of the T-cells antigen receptor (TCR) is of paramount importance; it is the first structure involved in the antigen (allergen) recognition, provided this one is presented in the right conditions; that is in the context of HLA molecules present at the surface of macrophages, after being processed inside. The TCR alpha/beta, present on more than 90% of peripheral T cells, is formed of two glyco-protein chains of similar molecular weight. The cytoplasmic end of the TCR is two short to transmit the message of recognition. The signal is transduced by neighbouring molecules forming the CD3 complex. Other membrane proteins such as CD2, LFA1, reinforce adhesion between immuno-competent cells. The presence or absence of CD4 or CD8 surface antigens, permit to distinguish two T cell subpopulations, namely helper and suppressor/cytotoxic lymphocytes. The TCR gene organization is very similar to that of light and heavy chains of immunoglobulins. Their fortuitous rearrangement explains the very large diversity of the T-cell repertoire. The TCR gamma/delta, although first appeared on the thymic cells, is present on less than 5% of peripheral lymphocytes, where its exact role is still unknown.