Cell-surface immunoglobulin expression in R406-sensitive and -resistant DLBCL cell lines. Cell-surface IgG (blue) and IgM (purple) expression in R406-sensitive (A) and -resistant (B) DLBCL cell lines were evaluated using standard immunophenotyping procedures and flow cytometry. As indicated, 5 of the R406-sensitive DLBCL cell lines expressed high levels of cell-surface IgG and 5 lines expressed surface IgM. Two of the R406-resistant cell lines were surface Ig negative and 3 lines had low/moderate levels of cell-surface IgG. Cells stained with an isotype-matched control Ig are shown in black.