The VavP-Bcl2 germinal center phenotype depends on CD4 T cells. Total number of splenic B cells of the indicated surface phenotype in C57BL/6 (n = 3), VavP-Bcl2 69 (n = 5), GK5 (n = 3), and GK5-VavP-Bcl2 69 (n = 5) mice. Although the expression of the GK5 transgene in otherwise healthy mice did not alter the number of B220⁺ B cells of either mature (IgM⁺ IgD⁺ κ⁺) or immunoglobulin class–switched (IgM^- IgD^- κ⁺) phenotype, it reduced the number of class-switched B cells in VavP-Bcl2 transgenic mice approximately 10-fold, while reducing the total number of mature B cells less than 2-fold.