ACTIVATION OF THE RESPIRATORY BURST IN EOSINOPHIL LEUKOCYTES - A TRANSDUCTION SEQUENCE DECOUPLED FROM CYTOSOLIC CA2+ RISE

The activation of the respiratory burst by complement factor 5a (C5a), platelet-activating factor (PAF), formyl-Met-Leu-Phe (fMLP) and neutr ophil-activating peptide IL-8 was explored in eosinophils from patient s with the hypereosinophilic syndrome. The amplitude of the response i ncreased with increasing concentrations of C5a and PAF, but the time f or its induction was unaffected by the amount of stimulus applied. Res piratory burst activity resulting from phorbol 12-myristate, 13-acetat e (PMA)-mediated activation of protein kinase C (PKC) produced longer onset times, which shortened with increasing PMA concentrations. Total inhibition of the C5a- and PMA-mediated burst could be achieved with the PKC inhibitor staurosporine at concentrations of 100 and 5 nM, res pectively. Calcium depletion abolished agonist-induced rises in cytoso lic free calcium ([Ca2+](i)) and respiratory burst activity, but not P MA-mediated NADPH-oxidase activation. While PMA reduced elevations in [Ca2+](i), it restored the burst response to agonists in Ca2+-depleted eosinophils. These results agree with the agonist-induced activation of the NADPH-oxidase via PKC, but suggest a parallel, Ca2+-, phospholi pase C- and PKC-independent signal transduction pathway. Data obtained with B. pertussis toxin showed that the respiratory burst in eosinoph ils is blocked by ADP-ribosylation of Gi-proteins, but that in the pre sence of PMA portions of the agonist response could be recovered.