Binding of carbonate-released exosomal IgM to apoptotic cells. Apoptosis was induced in Jurkat cells by treatment with an anti-FAS antibody (CD95) for 16 hours. Cells were then incubated with dialyzed carbonate wash from exosomes. After washing, cells were analyzed by flow cytometry for the presence of IgM. (Top panel) Dot plot (FCS vs SSC) defining 2 regions, R1 and R2, corresponding to apoptotic and nonapoptotic cells, respectively. (R1 and R2 panels) The 2 regions were analyzed for annexin V and IgM binding. (Bottom panels) IgM binding to apoptotic cells was carried out after preincubation of the carbonate wash to microplates coated with phosphatidylcholine (+PC; tinted pattern) or lysophosphatidylcholine (+LPC; tinted pattern) to deplete specific natural IgM antibodies. CTRL (–) carbonate wash was directly incubated with cells.