Abstract
Periostin is an extracellular matrix protein that is up-regulated by T helper cell type 2 cytokines in the asthmatic airway and implicated in mouse studies as promoting eosinophil recruitment. We asked whether periostin modulates eosinophil adhesion and motility in vitro. Periostin adsorbed to polystyrene supported adhesion of purified human blood eosinophils stimulated by IL-5, IL-3, or granulocyte/macrophage colony-stimulating factor, but did not support adhesion of eosinophils treated with IL-4 or IL-13. The degree of adhesion depended on the concentrations of periostin during coating and activating cytokine during the adhesion assay. Both full-length periostin and alternatively spliced periostin, lacking C-terminal exons 17, 18, 19, and 21, supported adhesion. Adhesion was inhibited by monoclonal antibody to α(M) or β(2) integrin subunits, but not by antibodies to other eosinophil integrin subunits. Adsorbed periostin also supported α(M)β(2)-dependent random motility of IL-5-stimulated eosinophils with optimal movement at an intermediate coating concentration. In the presence of IL-5, eosinophils adherent on periostin formed punctate structures positive for filamentous actin, gelsolin, and phosphotyrosine. These structures fit the criteria for podosomes, highly dynamic adhesive contacts that are distinct from classical focal adhesions. The results establish α(M)β(2) (CD11b/CD18, Mac-1) as an adhesive and promigratory periostin receptor on cytokine-stimulated eosinophils, and suggest that periostin may function as a haptotactic stimulus able to guide eosinophils to areas of high periostin density in the asthmatic airway.