Non-specific activation of human eosinophil functional responses by vasoactive intestinal peptide

Eosinophils and neuropeptides are thought to play effector roles in allergic diseases, such as rhinitis; however, little is known about the biological effects of neuromediators, especially vasoactive intestinal peptide (VIP), on eosinophil functional responses. In the present study, it is shown that VIP induces eosinophil chemotaxis and eosinophil-derived neurotoxin (EDN) release in potency comparable with that induced by platelet activator factor, and in a novel synergistic manner with recombinant human interleukin-5. Contrary to chemotaxis, EDN release was sensitive to staurosporine, the protein kinase C inhibitor, as well as intracellular calcium chelation. However, eosinophil treatment with inhibitors of tyrosine kinases (herbimycin A) and phosphatases (pervanadate) resulted in a dose-dependent potentiation and blockage of VIP-induced eosinophil chemotaxis, respectively. Treatment of eosinophils with VIP receptor antagonist did not modify VIP-induced chemotaxis or EDN release. Furthermore, exploration of vasoactive intestinal peptide receptor I expression was lacking in human eosinophils, but not lymphocytes. These results demonstrate two different mechanisms in triggering eosinophil activation of functional responses by VIP, a calcium-dependent degranulation and a calcium-independent chemotaxis, and elaborate on a novel cytokine–neuropeptide interaction in eosinophilic inflammation.