CHEMOTACTIC AGONISTS INDUCE CYTOKINE GENERATION IN EOSINOPHILS

Recent studies have shown that eosinophils are capable of generating a nd releasing cytokines, providing a novel biologic aspect of eosinophi ls for regulating allergic inflammation by an autocrine or paracrine m echanism. Eosinophils synthesize various cytokines; however, the physi ologic stimuli that trigger eosinophils to generate cytokines have not been fully elucidated. We examined the effect of chemotactic agonists on eosinophil cytokine generation by employing the determination of I L-8 as the main parameter. Both C5a and FMLP stimulated eosinophils to release IL-8, whereas platelet-activating factor and C-C chemokines d id not exert any significant effects. On a molar basis, C5a was two or ders of magnitude more potent than FMLP. The generation of IL-8 by che moattractants was absolutely dependent on the presence of cytochalasin B. Pertussis toxin completely attenuated C5a- and FMLP-induced IL-8 p roduction, indicating the involvement of pertussis toxin-sensitive G-p roteins in the signal-transduction process leading to these responses. Experiments of in situ hybridization and PCR amplification revealed t hat both C5a and FMLP promoted eosinophil IL-8 production through tran scriptional gene activation. Pyrrolidine dithiocarbamate completely ab rogated chemoattractant-induced IL-8 production, indicating the involv ement of NF-kappa B cytoplasmic/nuclear signal-transduction process. F urthermore, chemoattractant-induced cytokine production was not limite d to IL-8; C5a and FMLP but not platelet-activating factor induced sig nificant secretion of granulocyte-macrophage-CSF from eosinophils. The se results indicate that C5a and FMLP stimulate eosinophils to elabora te cytokines, which could be an important mechanism in the regulation of allergic inflammation.