α-BCR–induced signaling in MCL cells is associated with increased surface expression of BCR subunits CD79B and IgM. (A) Contour plots of CD20 expression vs CD79B or IgM expression in CLL, MCL, and healthy donor PBMC sample, respectively. (B) Expression of CD79B in lymphoma cells relative to T cells present in same sample in DLBCL, FL, CLL, MCL, and healthy donor tonsil and PBMC samples. (C) Association between α-BCR–induced p-PLCγ and CD79B surface expression in DLBCL, FL, and MCL. Each dot represents a patient sample. (D) Association between α-BCR–induced p-PLCγ and tumor heavy-chain expression (IgG or IgM for DLBCL, FL, and IgM for MCL). (E) The presence of 2 distinct lymphoma subclones in a MCL patient (MCL-R001), based on expression of CD5 and CD20, demonstrates potentiated α-BCR–induced phosphorylation events in the CD5^hiCD20^hi subclone. The CD20^hiCD5^hi cells are CD79B^hi, as compared with CD20⁺CD5⁺ lymphoma cells (see supplemental Figure 9E). DLBCL (n = 12), FL (n = 27), CLL (n = 14), MCL (n = 42). Healthy donor controls: tonsillar B cells (n = 4) and PBMC B cells (n = 5). Note that surface protein expression of CD79B and IgM were obtained as separate immunophenotypic staining, and not included in the signaling assay. Statistical difference was calculated using the Mann-Whitney nonparametric test (***P < .0001, **P < .005), and correlation was calculated by the Spearman rank test.