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Secretory Phospholipases A₂ Activate Selective Functions in Human Eosinophils¹

Massimo Triggiani^2,*, Francescopaolo Granata^*, Barbara Balestrieri^*, Angelica Petraroli^*, Giulia Scalia, Luigi Del Vecchio and Gianni Marone^*

^* Division of Clinical Immunology and Allergy, University of Naples Federico II, Naples, Italy; and Division of Hematology, A. Cardarelli Hospital, Naples, Italy

Secretory phospholipases A₂ (sPLA₂s) are released in large amounts in the blood of patients with systemic inflammatory diseases and accumulate at sites of chronic inflammation, such as the airways of patients with bronchial asthma. Blood eosinophils or eosinophils recruited in inflammatory areas therefore can be exposed in vivo to high concentrations of sPLA₂. We have examined the effects of two structurally different sPLA₂s (group IA and group IIA) on several functions of eosinophils isolated from normal donors and patients with hypereosinophilia. Both group IA and IIA sPLA₂ induced a concentration-dependent release of -glucuronidase, IL-6, and IL-8. Release of the two cytokines was associated with the accumulation of their specific mRNA. In addition, sPLA₂s induced the surface expression of CD44 and CD69, two major activation markers of eosinophils. In contrast, none of the sPLA₂s examined induced the production of IL-5, the de novo synthesis of leukotriene C₄ and platelet-activating factor, or the generation of superoxide anion from human eosinophils. Incubation of eosinophils with the major enzymatic products of the sPLA₂s (arachidonic acid, lysophosphatidylcholine, or lysophosphatidic acid) did not reproduce any of the enzymes’ effects. In addition, inactivation of sPLA₂ enzymatic activity by bromophenacyl bromide did not influence the release of -glucuronidase or of cytokines. Stimulation of eosinophils by sPLA₂s was associated with activation of extracellular signal-regulated kinases 1/2. These results indicate that sPLA₂s selectively activate certain proinflammatory and immunoregulatory functions of human eosinophils through mechanism(s) independent from enzymatic activity and from the generation of arachidonic acid.

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