Bcl10 protects primary B cells from apoptosis. Primary B cells were isolated from Balb/c mouse spleens and activated for 2 days with anti-IgM, anti-CD40, and IL-4. The cells were then infected with a retrovirus encoding Bcl10-IRES-GFP or a control retrovirus expressing only GFP. After another 2 days incubation with anti-IgM, anti-CD40, and IL-4, the cells were cultured in medium without stimuli. Triplicate cultures were sampled at different times via flow cytometry (A) for GFP expression, and the percentage of positive cells was determined (B; squares indicate Bcl10-expressing retrovirus; diamonds, vector only). To confirm that the surviving cells in the Bcl10-expressing cultures were B cells, they were stained with anti-CD19 or an isotype control antibody(C).