Carboxyfluorescein diacetate labeling does not affect adhesion molecule expression or function in human neutrophils or eosinophils

Fluorescently labeled leukocytes are commonly used in in vitro and in vivo experimental systems. However, the effects of fluorescent labeling on the expression and function of leukocyte adhesion molecules has not been examined in part because the extreme intensity of fluorescence tends to obscure signals from other fluorochromes used for dual color analysis. We have utilized a novel technique involving a 7-amino-4-methylcoumarin-3-acetic acid (AMCA) fluorophore-conjugated F(ab′)₂ fragment excitable in the ultraviolet wavelength range (350-450 nm) and dual-laser flow cytometry to determine if labeling of human neutrophils and eosinophils with the fluorescent dye 5-(6)-carboxyfluorescein diacetate (CFDA) alters surface expression of the primary leukocyte adhesion molecules involved in leukocyte-endothelial interactions. Simultaneously, adhesion molecule function was assessed by comparing the ability of CFDA-labeled vs. control cells to adhere to cultured human umbilical vein endothelial cells (HUVEC) and purified immobilized adhesion molecules. Isolated human eosinophils and neutrophils were fluorescently labeled by incubation with CFDA. Flow cytometric comparisons of labeled and unlabeled cells demonstrated that fluorescence labeling of neutrophils and eosinophils with CFDA did not alter basal surface expression of the β₂ integrins (i.e., CD11a CD11b or, CD18). Stimulation of neutrophils with fMLP and eosinophils with PMA resulted in increased surface expression of CD11b and CD18 which was not altered by CFDA labeling. Likewise, CFDA labeling of neutrophils and eosinophils did not significantly alter their integrin-dependent adhesion to activated HUVEC under static or rotational conditions. Similarly, adhesion to immobilized recombinant E- and P-selectin was unaltered. These data demonstrate that fluorescent labeling of human neutrophils and eosinophils with CFDA does not alter surface expression or function of several adhesion molecules necessary for leukocyte-endothelial interactions. The use of CFDA-labeled cells in experiments employing intravital microscopy should therefore provide valid information on adhesion molecule function in vivo.