BCR activation in normal and malignant GC B cells. (A) B cells were purified from tonsils and FL samples and were stimulated with soluble goat anti-human IgM or IgG Abs for indicated time points. BCR activation was revealed using intracellular staining for pSYK, pBLNK, and pERK. GC B cells were gated based on CD38^hi expression whereas IgM⁺ or IgG⁺ malignant FL B cells were further gated based on the expression of an appropriate tumor light chain (n = 5 for each subset). rMFI was obtained as the rMFI with/without BCR stimulation. Bars, mean ± SD. (B) GC B cells were sorted from purified tonsil B cells based on CD44⁻IgD⁻ phenotype. Sorted GC B cells and purified FL B cells were stimulated for 10 minutes with coated mouse anti-human IgM or IgG mAbs before fixation, permeabilization, and staining with rabbit anti-pCD79a primary mAbs followed by A488-donkey anti-rabbit secondary Ab, and A549-goat anti-human IgM or A549-donkey anti-human IgG Abs. pCD79a MFI was obtained for 50 cells per sample (pool of 3 GC B-cell samples, 6 IgM FL samples, 6 IgG FL samples). Scale bar, 2.5 µm. **P < .01; ***P < .001; FL-G, IgG⁺ FL; FL-M, IgM⁺ FL; GC-G, IgM⁺ GC B cells; GC-M, IgM⁺ GC B cells; ns, not significant; Uns, unstimulated.