Studies on the molecular basis of eosinophil adhesion to endothelium

Selective adhesion may be important for the preferential accumulation of eosinophils in asthma and allergic diseases. The Stamper-Woodruff frozen section assay (FSA) was used to define the adhesion of human peripheral blood eosinophils and neutrophils to endothelium in a model of chronic airway inflammation, the nasal polyp. Eosinophil and neutrophil adhesion to nasal polyp endothelium (NPE) was (32 integrin-dependent. Eosinophil adhesion was inhibited to a lesser extent by mAbs against pi integrins and VCAM-1. Adhesion of both eosinophils and neutrophils to NPE was activation-dependent. as shown by inhibition with azide. Neutrophil adhesion was mediated by PAF and IL-8 signalling through pertussis toxin (PTX)-scnsitive G-protein coupled receptors (GPCR). In contrast, eosinophil adhesion was PTX-insensitive. and the chemokine receptor CCR3 was not involved. The eosinophil activation step was further explored under shear flow conditions. Neutrophils firmly arrested on TNF-a-stimulated human umbilical vein endothelial cells (HUVEC) under flow. In contrast, eosinophils rolled unless exogenous chemoattractants such as PAF, eotaxin, and RANTES were added. Priming eosinophils with IL-5 before addition to HUVEC caused arrest of the entire population. The flow assay was also used to investigate the receptors involved in leukocyte adhesion to IL-13- stimulated HUVEC. Eosinophils but not neutrophils showed enhanced binding to IL-13- stimulated HUVEC compared to medium-cultured cells. This adhesion was mediated by P-selectin/ PSGL-1. and to a lesser extent VLA-4/ VCAM-1. These findings were consistent with the pattern of adhesion receptor expression in nasal mucosa, with weak expression of VCAM-1 compared with P-selectin. In summary, I have demonstrated a difference in integrin usage and the mechanism of integrin activation between eosinophils and neutrophils. An additional priming step in the adhesion cascade appears to be required for eosinophils, but not neutrophils, to respond to an activating stimulus and arrest on endothelium. P-selectin/ PSGL-1 interactions were pivotal to eosinophil arrest on Th2- cytokine-stimulated endothelium and are potential targets for inhibition of eosinophil migration.