Fcgamma receptor-mediated immune phagocytosis depends on the class of FcgammaR and on the immunoglobulin-coated target cell.

BACKGROUND AND OBJECTIVES: Three human Fcgamma receptors (FcgammaR) are known to mediate immune phagocytosis. A variety of different phagocytic assays have been described, but their comparability is complicated by the use of different effector cells and different antibody-coated target cells. The aim of this study was to determine the influence of these variable components on the FcgammaR-mediated phagocytosis.
MATERIALS AND METHODS: We sensitized human red blood cells (RBC) with polyclonal human anti-D (huaD), or with human monoclonal anti-D of the isotypes IgG1 (huIgG1) or IgG3 (huIgG3). Sheep RBC coated with rabbit immunoglobulin (RBC-RAS) were also used. Monocytes or polymorphonuclear neutrophils (PMN) were incubated with different FcgammaR-specific antibodies or their F(ab')2 fragments to determine the contribution of the different FcgammaRs on these effector cells in the phagocytic process of different antibody-coated target cells.
RESULTS: huaD-RBC and huIgG1-RBC were preferentially ingested via the FcgammaRI on monocytes and, to a minor extent, also by the FcgammaRII. PMN ingested these target cells only after induction of the FcgammaRI by interferon-gamma (IFN-gamma). huIgG3-RBC extensively formed rosettes with monocytes but were seldom ingested. RAS-RBC phagocytosis was induced primarily via the FcgammaRI on monocytes and was mediated by the FcgammaRII on PMN.
CONCLUSION: When performing phagocytosis assays with different effector and target cells, one has to take into account that phagocytosis is mediated by different FcgammaR, making comparability of these assays more difficult.