Induction of apoptosis in FcαRI RBL transfectants and blood monocytes by purified human IgA. (A) Comparison of apoptosis induction in chimeric FcαRI_R209L/γ RBL transfectants treated with different anti-FcαRI Fab fragments. Cells were incubated for 24 hours with 10 μg/mL A77, A62, A59, A3, or control (320) Fab fragments and the percentage of apoptotic cells was determined by analysis of the annexin V/PI double-positive population. One representative experiment of 3 is shown. (B) Induction of apoptosis in chimeric FcαRI_R209L/γ RBL transfectants and blood monocytes by IgA was measured in the presence of 10% or 0.5% serum. Cells were treated with 50 μg/mL human IgA or control human IgG for 10 hours before annexin V/PI staining. Values indicate the percentage of double-positive cells and are means ± SD of at least 3 separate experiments performed in duplicate. *P < .01. (C) Comparison of apoptosis induction in chimeric FcαRI_R209L/γ RBL transfectants after incubation with 50 μg/mL IgA and 10 μg/mL A77 Fab in the presence of 0.5% serum. After 10 hours cells were analyzed for annexin V/PI double-positivity as described in “Materials and methods.” Values indicate the percentage of double-positive cells and are means ± SD of at least 3 separate experiments performed in duplicate. (D) Analysis of apoptosis in chimeric FcαRI_R209L/γ RBL transfectants after treatment with 50 μg/mL human IgA (□) or control IgG (▪) in the presence of various percentages of serum (left panel) and after treatment with various concentrations of immunoglobulin in the presence of 0.5% serum (right panel). After 10 hours cells were analyzed for annexin V/PI double-positivity as described in “Materials and methods.” Values indicate the percentage of double-positive cells and are means ± SD of at least 3 separate experiments performed in duplicate. *P < .01.