Increased expression of CD11b and functional changes in eosinophils after migration across endothelial cell monolayers

Abstract

Eosinophils from sputum, nasal polyps, and bronchoalveolar lavages of asthmatics demonstrated a considerably increased CD11b expression, compared with blood eosinophils. Furthermore, the tissue eosinophils expressed ICAM-1 (CD54) and HLA-DR, whereas peripheral blood eosinophils did not. In vitro migration of peripheral blood eosinophils across IL-1-activated human umbilical vein endothelial cell monolayers caused a considerable up-regulation of CD11b and CD35 expression, no induction of ICAM-1 or HLA-DR, and a small but significant decrease in CD11a, CD29, and CD32 expression. These changes were only partially inducible with supernatants from nonactivated or IL-1-activated endothelial cells, platelet-activating factor, or a variety of recombinant cytokines. Thus, cell-cell interactions mediated by receptor-ligand binding or endothelial cell membrane-bound mediators, rather than soluble factors, are responsible for the altered eosinophil surface marker expression. Indeed, preparations of membrane fragments from IL-1-stimulated endothelial cells were able to induce up-regulation of CD11b, which was not inhibitable with the platelet-activating factor antagonist WEB 2086 or antibodies against ELAM-1, VCAM-1, or ICAM-1. Investigation of the functional significance of the increased CD11b expression on eosinophils revealed only minimal changes in the adherence or transmigration capacity. Nevertheless, increased CD11b expression was related to an increased capacity to generate superoxide after stimulation with opsonized zymosan. Thus, cell-cell interactions between eosinophils and endothelial cells induce a considerable up-regulation of CD11b and CD35 on eosinophils and an increased capacity to generate an oxidative burst.