A flow cytometric assay of Fc receptor-mediated phagocytosis

A flow cytometric assay was developed that specifically measures Fc receptor-mediated phagocytosis independent of other phagocytosis-related receptors. Suspensions of rat alveolar macrophages were incubated with fluorescein isothiocyanate (FITC)-labeled polystyrene microspheres and subsequently were analyzed by flow cytometry. Coating of microspheres with bovine serum albumin was used to generate ''neutral'' particles demonstrating low phagocytosis by alveolar macrophages (AMs). AM attachment and uptake of these particles was increased tenfold with IgG opsonization. This increase was abolished completely by blocking of AM Fc receptors with IgG. The quenching effect of ethidium bromide (EB) on FITC fluorescence was used for differentiating attached from internalized particles. The assay was standardized and optimized for use in toxicologic studies.