Structure and Specificity of a Class II MHC Alloreactive $\gamma \delta $ T Cell Receptor Heterodimer

Two distinct CD3-associated T cell receptors (TCR$\alpha \beta $ and TCR$\gamma \delta $) are expressed in a mutually exclusive fashion on separate subsets of T lymphocytes. While the specificity of the TCR$\alpha \beta $ repertoire for major histocompatibility complex (MHC) antigens is well established, the diversity of expressed $\gamma \delta $ receptors and the ligands they recognize are less well understood. An alloreactive CD3$^{+}$CD4$^{-}$CD8$^{-}$ T cell line specific for murine class II MHC (Ia) antigens encoded in the I-E subregion of the H-2 gene complex was identified, and the primary structure of its $\gamma \delta $ receptor heterodimer was characterized. In contrast to a TCR$\alpha \beta $-expressing alloreactive T cell line selected for similar specificity, the TCR $\gamma \delta $ line displayed broad cross-reactivity for multiple distinct I-E--encoded allogeneic Ia molecules.