The FcR γ chain is essential for both surface expression of and phagocytosis by hFcRI. (A) Genomic DNA from wild-type and FcR γ chain-deficient mice was checked for the presence of hFcRI and FcR γ chain by PCR. Wild-type FcR γ chain PCR products are marked by the closed arrowhead and positions of mutant FcR γ chains are marked by the open arrowhead. (B) Surface expression of hFcRI on granulocytes of Tg,γ⌈+/− (bold line), Tg,γ−/− (thin line), or NTg,γ⌈+/− (filled area) analyzed by flow cytometry. Cells were stained with A77-FITC. (C) Physical interaction between FcR γ chain and hFcRI was shown in Tg mice by FcR γ chain immunoadsorption with MoAb directed to hFcRI. The gel was run under nonreducing conditions and the blot was stained with a rabbit anti-FcR γ chain antiserum. Position of FcR γ chain homodimers is marked by the arrowhead. (D) Phagocytosis of IgA-coated PKH26-labeled bacteria by hFcRI/γ chain transfectants is dependent on a functional ITAM. Human secretory IgA-opsonized bacteria were incubated with hFcRI transfectant cells. FL-2 fluorescence represents bacterial binding to transfectants. After incubation at either 4°C or 37°C, remaining cell-surface bound bacteria was detected using GhIgA-FITC. A decrease in FITC-fluorescence (FL-1) reflects phagocytosis. One representative experiment of five is shown.