Activation of T lymphocytes by cross-linking of glycophospholipid-anchored Thy-1 mobilizes separate pools of intracellular second messengers to those induced by the antigen-receptor/CD3 complex.

T cells can be activated, not only by the conventional (antigen-receptor/CD3 complex) route, but also by cross-linking any one of their lipid-anchored surface glycoproteins. We have compared early transmembrane signalling events mediated through CD3 with those mediated through Thy-1, a lipid-linked surface glycoprotein, on the human lymphoid cell line Jurkat and transfectants expressing higher levels of Thy-1. Cross-linking of Thy-1 causes immediate phosphatidylinositol (PI) turnover and an influx of extracellular Ca2+, while releasing very little Ca2+ from intracellular stores. CD3 activation, on the other hand, causes PI turnover which releases intracellular Ca2+, and only secondarily induces an influx of extracellular ions. The Thy-1 response is detectable at very low levels of surface Thy-1, and is not mimicked by enzymatic removal of lipid-linked proteins from the cell surface. The Thy-1-induced Ca2+ influx is more sensitive to L channel blockers than the CD3-mediated flux. These results indicate that the initial stages of Thy-1-mediated activation involve the rapid and extensive mobilization of the intracellular second messengers, PI and Ca2+, by mechanisms separate to those activated by the antigen-receptor/CD3 complex.