Staphylococcus aureus directly activates eosinophils via platelet-activating factor receptor

Staphylococcus aureus (SA) directly activates eosinophils via PAF receptor to induce degranulation, superoxide, and cytokine production, suggesting that SA colonization has pathological significance in atopic dermatitis. Colonization by SA is associated with exacerbation of AD. Eosinophilic inflammation is a cardinal pathological feature of AD, but little is known about possible direct interaction between SA and eosinophils. PAFR appears to be involved in phagocytosis of Gram‐positive bacteria by leukocytes. The objective of this study was to investigate whether SA directly induces eosinophil effector functions via PAFR in the context of AD pathogenesis. Peripheral blood eosinophils were cultured with heat‐killed SA, and EDN release, superoxide generation, and adhesion to fibronectin‐coated plates were measured. Cytokines, released in the supernatants, were quantified by multiplex bead immunoassays. FISH‐labeled SA was incubated with eosinophils and visualized by confocal laser‐scanning microscopy. PAFR‐blocking peptide and PAFR antagonists were tested for inhibitory effects on SA‐induced reactions. SA induced EDN release and superoxide generation by eosinophils in a dose‐dependent manner. IL‐5 significantly enhanced SA‐induced EDN release. IL‐5 and IL‐17A significantly enhanced SA‐induced superoxide generation. SA enhanced eosinophil adhesion to fibronectin, which was blocked by anti‐CD49d, and induced eosinophil secretion of various cytokines/chemokines (IL‐2R, IL‐9, TNFR, IL‐1β, IL‐17A, IP‐10, TNF‐α, PDGF‐bb, VEGF, and FGF‐basic). After incubation of eosinophils with SA, FISH‐labeled SA was visualized in the eosinophilsˈ cytoplasm, indicating phagocytosis. A PAFR‐blocking peptide and two PAFR antagonists completely inhibited those reactions. In conclusion, SA directly induced eosinophil activation via PAFR. Blockade of PAFR may be a novel, therapeutic approach for AD colonized by SA.