CD2 SIGNALING IN T-CELLS INVOLVES TYROSINE PHOSPHORYLATION AND ACTIVATION OF THE TEC FAMILY KINASE, EMT ITK/TSK/

Ligation of the CD2 cell surface glycoprotein expressed on T lymphocyt es and NK cells induces protein tyrosine phosphorylation and activatio n of the Src kinases, LCK and FYN. We show here that in Jurkat T leuke mia cells and in peripheral blood T cells, CD2 stimulation also leads to tyrosine phosphorylation and activation of the Tec family kinase, E MT/ITK/TSK. Activation of EMT by CD2 was induced by mitogenic pairs of CD2 mAb, certain single CD2 mAb followed by secondary antibody cross- linking, and CD58-bearing sheep red blood cells. With the use of diffe rent Jurkat cell mutants it was demonstrated that CD2-mediated activat ion of EMT required expression of LCK, but did not require surface exp ression of the CD3 zeta chain. Receptor-mediated activation of LCK doe s not in itself lead to activation of this Tec kinase since induction of LCK by ligation of CD4 or CD5 did not result in activation of EMT. The activation of EMT during CD2 signaling suggests an important role for this kinase in CD2 co-stimulation of T cell responses.