Mechanisms involved in human eosinophil chemotaxis induced by the newly cloned C-C chemokine eotaxin

The present study was performed in order to investigate the mechanism(s) involved in eotaxin-induced normal human eosinophil chemotaxis using a 48-well micro-chemotaxis chamber assay. Eotaxin, at a wide range of doses, induced eosinophil chemotaxis with optimal activity at 100 ng/mL. To elucidate the role of Ca2+ as a second messenger, eosinophils were depleted of intracellular Ca2+ which, per se, did not modify eosinophil chemotaxis. To gain insight of the possible intracellular signal transduction, we blocked pertussis toxin (PTX)-sensitive Gj proteins as well as several protein kinases. It was found that the inhibition of tyrosine kinase with herbimycin A and the inhibition of mitogen-activated protein kinase (MAPK) with MEK-1 inhibitor (PD98059) significantly blocked chemotaxis; however, inhibition of protein kinase C with staurosporine, protein kinase A with H-89 and Gi proteins with PTX did not affect chemotaxis. These results suggest a signal transduction pathway(s) involving Ca2+-independent tyrosine kinase and MAPK activities

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

Evidence for interleukin-5 in nasal polyps in aspirin-induced asthma

Aspirin-induced asthma is often accompanied by nasal polyps, in which tissue eosinophils are abundant and activated. However, the mechanism of eosinophil infiltration remains unknown. We encountered two aspirin-induced asthma patients with nasal polyps and investigated eosinophil infiltration into nasal polyp tissue. Eosinophil chemotactic activity of extracts from the nasal polyp was elevated and could be inhibited by 40% with anti-interleukin (IL)-5 antibody. Interleukin-5 was detectable in the extract. The chemotactic activity of peripheral blood eosinophils to recombinant human (rh)IL-5 was increased compared with normal volunteers. Messenger RNA expression for IL-5 in CD3+ lymphocytes for polyp tissue was detected using the reverse transcription-polymerase chain reaction. These results suggest that IL-5 from local T lymphocytes may be one of the candidates for recruitment of eosinophils into nasal polyps in aspirin- induced asthma