Involvement of protein tyrosine kinases in activation of human eosinophils by platelet-activating factor

Activation of human eosinophils by platelet-activating factor (PAF) involves multiple signal transduction pathways. Among these, protein kinase C has been demonstrated both to mediate respiratory burst and to suppress an alternative pathway of activation of respiratory burst and arachidonic acid metabolism in eosinophils. We utilized inhibitors of protein tyrosine kinases (PTK) to elucidate the role of PTK in PAF-induced activation of eosinophils. Eosinophils were isolated from peripheral blood of atopic donors and stimulated with PAF in the absence or presence of broad-spectrum PTK inhibitors - genistein or lavendustin A; an inhibitor of mitogen-activated protein (MAP) kinase activation - tyrphostin AG126; or an inhibitor of Janus kinase 2 (Jak2) - tyrphostin B42 (AG490). PAF induced superoxide anion (O-2 .(-)) generation, leukotriene C-4 (LTC4) release, intracellular calcium ion mobilization and tyrosine phosphorylation of multiple eosinophil proteins in a concentration-dependent manner. All of these responses were concentration-dependently inhibited by genistein; lavendustin A also exhibited potent inhibition of PAF-induced LTC4 release. AG126 had no effect on either O-2 .(-) generation or LTC4 release, while AG490 inhibited both responses, albeit less effectively than genistein. We conclude that PAF activates PTK in human eosinophils and that this signalling pathway is involved in eliciting respiratory burst and leukotriene production. The specific PTK(s) involved are unknown but may include Jak2.