Differential Basal Protein Tyrosine Phosphorylation in Natural Killer (NK) and T Cells: A Biochemical Correlate of Lymphoid Functional Activity

Despite the similarities between natural killer (NK) and T cells, these lymphocytes have dramatically different functional phenotypes. To identify potential biochemical parameters that correlate with the “primed” NK phenotype, we have investigated protein tyrosine phosphorylation in NK and T cells. Examination of tyrosyl phosphorylation in NK cells showed that they have higher levels of phosphorylation than resting T cells. Consistent with this, the concentrations of the tyrosine kinase inhibitor, herbimycin A, required to inhibit FcR-mediated Ca2+flux in NK cells were much higher than those required for inhibition of T cell receptor-mediated Ca2+mobilization. Differences in phosphorylation were not due to purification artifact or explained by differential expression of the prominent lymphocyte src-family kinase, p56lckor the protein tyrosine phosphatase CD45. Thus, we have identified high basal tyrosyl phosphorylation as a striking biochemical feature of NK cells that correlates with the unique functions of this subset.