Stoichiometry of the murine γδ T cell receptor

The T cell receptor for antigen (TCR) complex is organized into two functional domains: the antigen-binding clonotypic heterodimer and the signal-transducing invariant CD3 and TCR zeta chains. In most vertebrates, there are two different clonotypic heterodimers (TCR alpha beta and TCR gamma delta) that define the alpha beta and gamma delta T cell lineages, respectively. alpha beta- and gamma delta TCRs also differ in their invariant chain subunit composition, in that alpha beta TCRs contain CD3 gamma epsilon and CD3 delta epsilon dimers, whereas gamma delta TCRs contain only CD3 gamma epsilon dimers. This difference in subunit composition of the alpha beta- and gamma delta TCRs raises the question of whether the stoichiometries of these receptor complexes are different. As the stoichiometry of the murine gamma delta TCR has not been previously investigated, we used two quantitative immunofluorescent approaches to determine the valency of TCR gamma delta heterodimers and CD3 gamma epsilon dimers in surface murine gamma delta TCR complexes. Our results support a model of murine gamma delta TCR stoichiometry in which there are two CD3 gamma epsilon dimers for every TCR gamma epsilon heterodimer.