Disruption of the <i>Bcl6</i> Gene Results in an Impaired Germinal Center Formation

The Bcl6 gene has been identified from the chromosomal translocation breakpoint in B cell lymphomas, and its products are expressed highly in germinal center (GC) B cells. To investigate the function of Bcl6 in lymphocytes, we have generated RAG1-deficient mice reconstituted with bone marrow cells from Bcl6-deficient mice (Bcl6−/−RM). Lymphogenesis in primary lymphoid tissues of Bcl6−/−RM is normal, and Bcl6−/−RM produced control levels of primary IgG1 antibodies specific to T cell–dependent antigens. However, GCs were not found in these mice. This defect was mainly due to the abnormalities of B cells. Therefore, Bcl6 is essential for the differentiation of GC B cells.