Actin assembly is a crucial factor for superoxide anion generation from adherent human eosinophils

Abstract

Background: Cellular adhesion is crucial for eosinophil effector functions. Objective: We sought to elucidate the role of the actin cytoskeleton in cellular adhesion and superoxide anion generation by human eosinophils. Methods: Eosinophils were stimulated with platelet-activating factor (PAF) or complement component 5a on human serum albumin - coated plates with or without an actin-polymerization inhibitor, cytochalasin B (CB), or cytochalasin D (CD). Superoxide anion generation was measured on the basis of reduction of absorbance associated with cytochrome c. Eosinophil adhesion was assessed on the basis of eosinophil protein X content in adherent cells. Transient stimulus-induced increase of intracellular calcium and translocation of protein kinase C (PKC) βII, PKC δ, PKC ζ, and p47 phagocyte oxidase (a component of nicotinamide adenine dinucleotide phosphate oxidase) were also investigated. Results: CB, CD, or antibodies against CD18 (the β2 chain of integrin, αMβ2) inhibited stimulus-induced eosinophil superoxide anion generation. Stimulus-induced eosinophil adhesion was unaltered by CB, whereas it was significantly suppressed by CD or anti-CD18 antibodies. Transient PAF-induced intracellular calcium increase was also unaffected by CB or CD, but stimulus-induced eosinophil shape changes and translocation of PKCs and p47 phagocyte oxidase to the cell membrane region were completely inhibited by CB. PAF-induced eosinophil degranulation was inhibited by CB, CD, or anti-CD18 antibodies, whereas complement component 5-induced degranulation was not suppressed by CB. Conclusion: By itself, β2 integrin - dependent cellular adhesion is not sufficient for promoting eosinophil effector function. Adequate actin assembly is required for eosinophil adhesion and also for full superoxide anion generation in eosinophils.