Topographic Distribution of CD18 Integrin on Human Neutrophils as Related to Shape Changes and Movement Induced by Chemotactic Peptide and Phorbol Esters

The acquisition of high-affinity ligand binding may result from a topographical redistribution of β2 integrins (CD11/CD18) in the plane of the membrane in response to agonist-induced neutrophil stimulation. We examined the topographical distribution of CD18 on human neutrophils in relation with shapes changes and movements induced by stimulation with 10−8M N-formylmethionyl-leucyl-phenylalanine (fMLP) and 10−7Mphorbol myristate acetate (PMA). To localize CD18, we used immunogold-labeling methods and backscattered electron images obtained with scanning electron microscopy. On unstimulated neutrophils, CD18 integrin was randomly distributed on the nonvillous planar cell body. Stimulation of neutrophils with 10−8MfMLP and 10−7MPMA for 10 min induced distinctive shape changes, i.e., polar and nonpolar ruffled shapes, and upregulation of the surface membrane content of CD18. These changes were accompanied by a specific topographic distribution of CD18. fMLP-stimulated (10−8M) cells accumulated CD18 on the ruffled plasma membrane at the frontal pole of polar neutrophils. PMA-stimulated (10−7M) cells displayed CD18 aggregates on all plasma membrane domains, mainly on ruffles of nonpolar ruffled neutrophils. We conclude that the motile neutrophil responses elicited by chemotactic peptide and phorbol ester are associated with distinct patterns of topographic distribution of CD18 integrin. These features of CD18 expression may influence adhesive interactions mediated by human neutrophils.