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Cell surface distribution of Fc receptors II and III on living human neutrophils before and during antibody dependent cellular cytotoxicity

Microscopic techniques have been employed to study the cell surface distributions of the immunoglobulin Fc receptors (FcR) II and III on living human neutrophils. Fluorescein‐ or rhodamine‐conjugated monoclonal IgG or Fab fragments directed against FcRII (CDw32) and FcRIII (CD16) were employed to label receptors. FcRII and III were found to be uniformly distributed at neutrophil surfaces during resting conditions. During neutrophil polarization and migration FcRII but not FcRIII preferentially accumulated at the uropod. Sheep erythrocytes (SRBCs) were opsonized with IgG and then incubated with neutrophils. When neutrophils were labeled prior to target addition, FcRII but not FcRIII were found to cluster at the target‐effector interface. Little or no clustering of FcRs was observed if labeling was performed after target binding. SRBC oxidation was observed using Soret band illumination during transmitted light microscopy. Time‐lapse studies of FcRII distribution and target oxidation were performed. FcRII formed clusters at target‐effector interfaces prior to target oxidation. Three lines of evidence suggest that clustering is not a general plasma membrane response. Firstly, FcRIII do not cluster. Tannic acid‐modified erythrocytes avidly bound to neutrophils but did not trigger clustering of FcRII. Furthermore, irrelevant neutrophil membrane labels were unaffected by the presence of IgG‐opsonized erythrocytes. We suggest that FcRII clustering is one important component leading to the oxidative destruction of target cells.