Structurally distinct T cell receptor complexes on developmentally distinct T cell populations in severe combined immunodeficiency mice expressing a TCRβ transgene

T cell differentiation and TCR expression were assessed in severe combined immunodeficiency (SCID) mice possessing an already rearranged TCRVβ8 transgene. Unlike nontransgenic SCID mice, TCRVβ8-transgenic SCID mice contained a broad spectrum of T cell populations, including both immature thymocytes and mature T cells. In TCRVβ8-transgenic SCID mice, immature CD4^-CD8^- and CD4⁺CD8⁺ thymocytes expressed surface TCR complexes structurally distinct from those expressed by mature single-positive T cells. Immature CD4⁺ CD8⁺ thymocytes expressed surface TCRβ chains without a clonotypic TCR partner chain and largely without associated CD3 components. In contrast, mature single-positive T cells expressed fully assembled surface TCR complexes containing disulfide-linked heterodimers consisting of transgenic TCRβ chains and endogenous TCRα chains. The surface TCR complexes on mature T cells were associated with CD3 components and were competent to transduce TCR-mediated proliferative signals. Thus, T cells at different stages of development in TCRVβ8-transgenic SCID mice express structurally distinct surface TCR complexes, demonstrating that the developmental stage achieved by T cells in these mice is related to the structure of the surface TCR complexes they express. Indeed, the present results indicate that successful differentiation into single-positive T cells requires surface expression of fully assembled TCR complexes.