Activation of CLL cells by binding of their autoantigenic BCR target. (A) Binding of the BCR-specific autoantigenic target SMCHD1 from patient 45 to his CLL cells induced an increase of cytoplasmic calcium concentration. [Ca²⁺]_intern was determined by flow cytometry using Fluo-4 dye (final concentration 2 µM). 1, PBMC (negative control); 2, PBMC + αIgM (positive control); 3, PBMC + unspecific antigen PC9; 4, PBMC + specific antigen SMCHD1; 5: PBMC + specific antigen SMCHD1 + ionomycin. (B) Time course of activation of CLL cells after binding of their autoantigenic BCR target. Binding of the BCR-specific autoantigenic target SMCHD1 from patient 45 to his CLL cells induced a fast increase of cytoplasmic calcium concentration followed by a slow decrease. [Ca²⁺]_intern was determined by flow cytometry in intervals of 30 seconds after addition of the antigen SMCHD1 (time [t] = 0). 1, dye-loaded cells without antigen; 2, 30 seconds; 3, 60 seconds; 4, 90 seconds; 5, 120 seconds; 6, 150 seconds. (C) Number of Fluo-4–responding cells after binding of their autoantigenic BCR target. Data taken from panel B.