γδ T cells — innate immune lymphocytes?

It is unclear what the antigen recognition determinants of γδ T-cell receptors (TCRs) are. Compared with immunoglobulin and αβ TCRs, γδ TCRs have the highest potential CDR3 diversity generated by VDJ recombination. However, γδ T-cell reactivities seem to segregate with V gene usage, which has been taken to suggest that rearrangement has little role in generating different antigen specificities. During the past year, the CDR3 regions were found to determine the antigen specificities of T10- and T22-reactive γδ TCRs, a surface protein complex was identified as a ligand for human phosphoantigen-reactive γδ T cells, and the first co-crystal structure of a γδ TCR bound to its ligand was reported. These advances warrant a fresh look at γδ T-cell antigen recognition.