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Essentially pure preparations of normal density eosinophils obtained from patients with hypereosinophilic syndrome (HES) were stimulated with complement factor 5a (C5a), platelet-activating factor (PAF), FMLP and neutrophil-activating peptide (NAP-1/IL-8). Three responses were studied, the transient rise in cytosolic free calcium concentration (ICa2+j (derived from indo-1 fluorescence), shape changes (measured by laser turbidimetry), and exocytosis of eosinophil peroxidase (EPO) (assessed by H202/luminol-dependent chemiluminescence). Responses were obtained with all four agonists, but C5a and PAF were by far more potent than FMLP and NAP-1/IL-8, which induced only minor effects. Pretreatment of the cells with pertussis toxin attenuated ICa2+h changes, EPO release and, to a lesser extent, shape changes, indicating that GTP-binding proteins of Gi-type are involved in receptor-dependent signal transduction processes leading to these responses. A clear dissociation was observed in the control of the shape change response and EPO exocytosis. The shape change was not affected by Ca2' depletion or treatment with the protein kinase inhibitor staurosporine, but exocytosis was prevented by Ca2' depletion and markedly enhanced by staurosporine. The activation of the contractile system, leading to shape changes and motility, thus appears to be independent of the classical signal transduction pathway involving phospholipase C, a [Ca2j11 rise and protein kinase C activation. Exocytosis is, as expected, CIO+ dependent and appears to be under a negative control involving protein phosphorylations. (J. Clin. Invest.

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The effects of anaphylatoxin C3a on human neutrophils were studied in comparison with C5a. Both peptides induced a transient shape change response and a respiratory burst. In both cases C3a was 50-to 100-times less potent than C5a. A marked chemotactic response with bimodal concentration dependence was obtained with C5a, but no neutrophil chemotaxis was observed with C3a. Repeated stimulation led to homologous desensitization of shape changes and respiratory burst but no cross-desensitization, indicating that the two anaphylatoxins act through separate receptors. The lack of chemotactic activity suggests that C3a is not involved in neutrophil recruitment into infected or inflamed tissues.