Biochemical Evidence for the Presence of a Single CD3δ and CD3γ Chain in the Surface T Cell Receptor/CD3 Complex

The T cell antigen receptor (TCR) consists of an αβ heterodimer and associated invariant CD3γ, δ, ϵ, and ζ chains (TCR/CD3 complex). The general stoichiometry of the receptor complex, which is believed to be one molecule each of TCRα, TCRβ, CD3γ, and CD3δ and two molecules each of CD3ϵ and CD3ζ, is not clearly understood. Although it has been shown that there are two chains of CD3ϵ and CD3ζ, the stoichiometry of CD3γ or CD3δ chains in the surface antigen receptor complex has not been determined. In the present study, transgenic mice expressing an altered form of mouse CD3δ and CD3γ were employed to show that the surface TCR complexes contain one molecule each of CD3δ and CD3γ. Thymocytes from wild type and CD3 chain transgenic mice on the appropriate knockout background were surface-biotinylated and immunoprecipitated using a specific antibody. The immunoprecipitates were resolved in two dimensions under nonreducing/reducing conditions to determine the stoichiometry of CD3δ and CD3γ in the surface antigen receptor complex. Our data clearly show the presence of one molecule each of CD3δ and CD3γ in the surface TCR/CD3 complex.