Stoichiometry of the T cell Antigen Receptor ( TCR ) Complex : Each TCR / CD 3 Complex Contains One TCR ol , One TCR [

The stoichiometry of the subunits that comprise the T cell antigen receptor (TCR) complex is not completely known. In particular, it is uncertain whether TCR ot and TCR/5 proteins are present in the TCR complex as one or multiple heterodimeric pairs. In this study we have used mice transgenic for two different TCR ot and two different TCR/5 proteins to determine the number of TCR a and TCR/5 chains in a single TCR complex. Individual thymocytes and splenic T cells from double TCR transgenic mice simultaneously expressed all four transgenic TCR proteins on their surfaces. Because the individual TCR ot and individual TCR/5 proteins were biochemically distinguishable, we were able to examine associations among the transgenic TCR products. We found that each TCR ct chain paired with each TCR/5 chain, but that each TCR complex contained only one TCR ot and one TCR B protein. Furthermore, quantitative immunofluorescence revealed that T cells expressed twice as many CD3e as TCR/5 proteins. These findings demonstrate that there are precisely one TCR a , one TCR/5, and two CD3e chains in each TCR/CD3 complex expressed on the surfaces of both thymocytes and mature T cells.