Tumor cell–specific BCR-mediated Btk, Syk, Erk1/2, and p38 signaling. Flow cytometry contour plots of FL patient biopsy cells (FL-P09) stimulated by BCR cross-linking plus H₂O₂ (α-μ/γ + H₂O₂) for 4 or 30 minutes or left unstimulated (0 minute). BCR-mediated phosphorylation of Btk, Syk, Erk1/2, and p38 was compared in FL B cells (CD20⁺ Bcl-2^hi λ^–, dark arrow) and nonmalignant B cells (CD20^hi Bcl-2^lo, light arrow).