Eosinophil tissue recruitment to sites of allergic inflammation in the lung is platelet endothelial cell adhesion molecule independent

Platelet endothelial cell adhesion molecule (PECAM or CD31) is a cell adhes ion molecule expressed on circulating leukocytes and endothelial cells that plays an important role in mediating neutrophil and monocyte transendothel ial migration in vivo. In this study, we investigated whether eosinophils, like neutrophils and monocytes, utilize PECAM for tissue recruitment to sit es of allergic inflammation in vivo. Eosinophils express similar levels of PECAM as neutrophils as assessed by FACS analysis. RT-PCR studies demonstra te that eosinophils like neutrophils; express the six extracellular domains of PECAM. Eosinophils exhibit homophilic binding to recombinant PECAM as a ssessed in a single-cell micropipette adhesion assay able to measure the bi ophysical strength of adhesion of eosinophils to recombinant PECAM. The str ength of eosinophil adhesion to recombinant PECAM is the same as that of ne utrophil binding to recombinant PECAM and can be inhibited with an anti-PEC AM Ab. Although eosinophils express functional PECAM, anti-PECAM Abs did no t inhibit bronchoalveolar lavage eosinophilia, lung eosinophilia, and airwa y hyperreactivity to methacholine in a mouse model of OVA-induced asthma in vivo. Thus, in contrast to studies that have demonstrated that neutrophil and monocyte tissue recruitment is PECAM dependent, these studies demonstra te that eosinophil tissue recruitment in vivo in this model is PECAM indepe ndent.