A FLOW CYTOMETRIC ASSAY OF FC RECEPTOR-MEDIATED PHAGOCYTOSIS

A flow cytometric assay was developed that specifically measures Fc re ceptor-mediated phagocytosis independent of other phagocytosis-related receptors. Suspensions of rat alveolar macrophages were incubated wit h fluorescein isothiocyanate (FITC)-labeled polystyrene microspheres a nd subsequently were analyzed by flow cytometry. Coating of microspher es with bovine serum albumin was used to generate ''neutral'' particle s demonstrating low phagocytosis by alveolar macrophages (AMs). AM att achment and uptake of these particles was increased tenfold with IgG o psonization. This increase was abolished completely by blocking of AM Fc receptors with IgG. The quenching effect of ethidium bromide (EB) o n FITC fluorescence was used for differentiating attached from interna lized particles. The assay was standardized and optimized for use in t oxicologic studies.