Regulated T-cell development: a victim of multiple conspiracies.

Abstract

Over about 400 million years there has been a conserved subdivision of T cells into those bearing a γδ T-cell receptor (TCR) and those bearing an αβ TCR. No one is sure why this is, but the two cell types have some interesting distinguishing characteristics, particularly their antigen specificities and their anatomical homing.1 In addition, the development of γδ cells seems always to precede that of αβ T cells. This is a good thing for γδ cells, because the TCRδ locus lies embedded within the TCRα locus, and when TCR Vα and Jα gene segments rearrange, they delete the TCRδ genes. Unchecked, this would substantially reduce the chances of making γδ cells.