BCL6 represses many oncogenes in centroblasts. (A) A heatmap is shown representing the transcript abundance (data from Basso²⁶ ) of oncogenes and related genes that are direct transcriptional targets of BCL6 (NBC indicates naive B cells; CB, centroblasts; and CC, centrocytes). (B) The relative ratio of BCL2 to BCL6 mRNA abundance versus GAPDH was measured in 3 independent sets of human tonsilar NBC and CBs by quantitative PCR (error bars represent the SEM for triplicates), and (C) Western blots. (D) Human tonsil sections were submitted to immunohistochemistry with BCL2 and nuclear counterstain (right panel and inset), BCL6 antibody and counterstain (middle), and with PAX5 and BCL2 costaining. The data show inverse staining patterns of BCL6 and BCL2 in GCs and show that the PAX5-positive GC B cells lack BCL2, indicating the BCL2-positive GC cells are not of the B-cell lineage. Slides were viewed with a light microscope (AxioSkop2; Carl Zeiss Microimaging, Thornwood, NY) using Plan-Neofluar lens at a 10×/0.50 air objective, 40×/0.90 oil objective, 100×/1.30 oil objective. Images were taken using a color camera (AxioCam; Carl Zeiss Microimaging) and were processed using Axiovision software (Carl Zeiss Microimaging).