sgp-60, a signal-transducing glycoprotein concerned with T cell activation through the T cell receptor/CD3 complex

T cell activation depends not only on the expression of a TCR, but also on that of accessory molecules that function in cell-cell adhesion and/or signal transduction. The subject of this report is the biochemical and functional characterization of what appears to be a novel murine lymphocyte cell surface antigen, provisionally termed sgp-60. Extensive, higher-order cross-linking of this glycoprotein with an anti-sgp-60 mAb and a second-step antibody reagent results in the activation of resting CD4+ T cells in the presence of a second signal. Monovalent or bivalent engagement of sgp-60 by the anti-sgp-60 antibody results in profound and direct inhibition of anti-CD3- or Con A-driven T cell activation, whereas alternative T cell activation via the phosphatidylinositol-linked proteins Thy-1 and TAP/Ly-6A is not affected. These findings raise the possibility that the sgp-60 molecule may be specifically involved in signal transduction through the TCR/CD3 complex and thus point to an important physiologic role for this protein in CD4+ T cells.