Human basophils activated through high-affinity immunoglobulin E (IgE) receptors (Fc epsilon RI) are involved in the late phase of the allergic reaction, To investigate the possible involvement of protein-tyrosine kinases in this activation we used human acute basophilic leukemia (ABL) cells in culture as well as a pure population of normal basophils in vitro-derived from human bone marrow precursor cells (HBMB), ABL cells were 50-80% basophils at various stages of maturation as assessed by staining, morphology, ultrastructure, and flow cytometry analysis, and only basophils in ABL cells expressed Fc epsilon RI, Aggregation of Fc epsilon RI by IgE and anti-IgE, IgE and antigen, or anti-Fc epsilon RI monoclonal antibodies on ABL cells or on HBMB, led to increased tyrosine phosphorylation of 120-, 100-, 80-, 72-, 50- to 65-, and 38-kDa substrates, Tyrosine phosphorylations in ABL cells were in basophils because 1) they were detected after a 5-s stimulation, 2) they were observed under conditions where mediator release is minimal, i.e., in the absence of extracellular calcium, 3) hapten-addition during antigen stimulation resulted in almost total disappearance of tyrosine phosphorylations within 30 s. There was correlation between histamine release and tyrosine phosphorylation in anti-IgE dose-responses and in dose-responses of the tyrosine kinase inhibitor genistein, The tyrosine kinase p72(syk) was detected in the cells, Stimulation of ABL cells for 1 min resulted in extracellular calcium-independent tyrosine phosphorylation and activation of p72(syk) Therefore, tyrosine kinases are involved in the early steps of human Fc epsilon RI signaling in basophils, Tyrosine kinases and their substrates could represent new potential therapeutic targets to prevent the development of the allergic reaction.
