Phagocytosis mediated by the chimeric receptor I-IIA-IIA in COS-1 cells expressing the I-IIA-IIA chimera alone or the I-IIA-IIA chimera plus the FcγRIIB mutant lacking a cytoplasmic domain, Trun-B2. (A) The percent of cells phagocytosing EA and the phagocytic index for three representative experiments are shown. (B) Expression of the chimeric receptor I-IIA-IIA as determined by flow cytometry. Cells were stained with MoAb 32.2 to measure I-IIA-IIA expression in the presence (–––––) or absence (.........) of Trun-B2. (. . . .), Indicates transfectants stained with isotype control antibody. The expression (MFI) of I-IIA-IIA was the same in the presence or absence of Trun-B2 in each experiment. The expression of Trun-B2 was determined by staining with anti-FcγRII MoAb IV.3. MFI for Trun-B2 in experiments 1, 2, and 3 was 55, 44, and 60, respectively.