The Expanding Universe of γ δ T Lymphocytes: Subsets, Generation and Function

γδ T cells which express the Vγ9 and Vδ2 gene products are unique to primates and represent only a minor population of peripheral blood T lymphocytes. They recognize nonpeptidic phosphoantigens in an MHC-unrestricted fashion and show low dependence on costimulation. The ability of Vγ9Vδ2 T cells to develop immunological memory remains debated. Vγ9Vδ2 T cells are able to mount both immediate effector functions and memory anamnestic responses upon microbial reinfection, suggestive of the existence of different functional subsets. However, how Vγ9Vδ2 T cells mediate the different facets of a memory response remains largely obscure. In this review we highlight recent findings that demonstrate that Vγ9Vδ2 cells are a very heterogeneous population of T lymphocytes and possess phenotypic and functional features very close to those of conventional αβ T lymphocytes: they comprise distinct naive, memory and effector populations that can be distinguished on the basis of surface markers expression, migratory properties and effector functions.