T cell receptor-mediated signaling occurs in the absence of inositol phosphate production

Murine cytotoxic T lymphocytes (CTL) can lyse certain target cells in the presence or absence of extracellular Ca²⁺ (Ostergaard, H.L., Kane, K.P., Mescher, M.F., and Clark, W.R. (1987) Nature 330, 71-72). We have examined the effect of extracellular Ca²⁺ on the inositol phosphate response to antigen by CTL. In Ca²⁺-containing medium relevant antigen-bearing target cells and the mitogen concanavalin A induce a rapid accumulation of inositol phosphates in CTL. In the presence of 4 mM EGTA the antigen- and mitogen-stimulated increases in inositol mono-, bis-, and tris-phosphates cannot be detected, even with 10 mM LiCl added. Abrogation of the inositol phosphate response occurs whether CTL are preincubated in EGTA or EGTA is added with the stimulus. The results indicate that the killing of certain target cells by murine CTL may be independent of the involvement of the phosphatidylinositol pathway. Furthermore, since Ca²⁺-independent cytolysis remains antigen-specific, the data strongly support the existence of additional T cell receptor-mediated second messenger pathway(s) in CTL.