Activation-induced Modification in the CD3 Complex of the γδ T Cell Receptor

The T cell antigen receptor complexes expressed on αβ and γδ T cells differ not only in their respective clonotypic heterodimers but also in the subunit composition of their CD3 complexes. The γδ T cell receptors (TCRs) expressed on ex vivo γδ T cells lack CD3δ, whereas αβ TCRs contain CD3δ. While this result correlates with the phenotype of CD3δ^−/− mice, in which γδ T cell development is unaffected, it is inconsistent with the results of previous studies reporting that CD3δ is a component of the γδ TCR. Since earlier studies examined the subunit composition of γδ TCRs expressed on activated and expanded peripheral γδ T cells or γδ TCR⁺ intestinal intraepithelial lymphocytes, we hypothesized that activation and expansion may lead to changes in the CD3 subunit composition of the γδ TCR. Here, we report that activation and expansion do in fact result in the inclusion of a protein, comparable in mass and mobility to CD3δ, in the γδ TCR. Further analyses revealed that this protein is not CD3δ, but instead is a differentially glycosylated form of CD3γ. These results provide further evidence for a major difference in the subunit composition of αβ- and γδ TCR complexes and raise the possibility that modification of CD3γ may have important functional consequences in activated γδ T cells.