Diversity, Development, Ligands and Probable Functions of γδ T Cells

The most critical step in the vertebrate immune response is the recognition of antigens by lymphocytes. This task is accomplished by two sets of glycoproteins, immunoglobulins and T cell antigen-receptors (TCRs). The most extraordinary feature of these proteins is their structural variability, much of which originates from the ability of the encoding gene segments to undergo somatic rearrangement.1 All TCRs were initially thought to be composed of a heterodimeric protein composed of α and β subunits. However, the search for the genes encoding these polypeptides led to the identification of a third rearranging gene2,3 which was later shown to code for one of the two subunits of another heterodimeric, TCR γδ.4–6