Reduced phagocytosis in p85α^–/– BMMs. Phagocytosis assay was performed using WT and p85α^–/– BMMs as described in “Materials and methods.” Phagocytosis assay was initiated by subjecting BMMs to IgG-sensitized sRBCs at a target-effector ratio of 100:1 for 15 minutes at 37°C. Nonengulfed sRBCs were lysed by water shock treatment and cells were fixed and stained using Diff-Quik stain before measuring the phagocytic index. (A) Arrows indicate engulfed cells. Images were acquired through a Zeiss Axioskop 2 Plus microscope equipped with a Plan-Neofluar 20×/0.5 objective lens, and were captured with an Axiocam MRC-5 camera and Axiovision 4 software (all from Zeiss, San Marcos, CA). (B) Bars indicate the mean phagocytic index ± SD. Data are from 4 independent experiments. *P<.05 for WT versus p85α^–/–. The ability of WT and p85α^–/– BMMs to bind IgG-sRBCs was assessed as described in “Materials and methods.” (C) Shown is the percent of BMMs bound to IgG sRBCs ± SD. (D) Expression of FcγIII/II receptor on WT and p85α^–/– BMMs was analyzed by using an anti-FcγIII/II receptor (CD16/32) antibody or an isotype control antibody and flow cytometric analysis. Solid histograms indicate the level of FcγIII/II receptor staining on the surface of both WT (97.94% positivity) and p85α^–/– (98.33% positivity) BMMs. Open histograms show the level of staining using an isotype control antibody.