Splenic T1 B cells are lost in tPtch^−/− mice. Splenocytes of vehicle-treated Ptch^flox/floxERT2^+/− or tamoxifen-treated Ptch^flox/floxERT2^−/− controls and of day-19 tPtch^−/− mice were analyzed by flow cytometry using antibodies against B220, CD21, CD24, IgM, and IgD to distinguish T1, T2, and mature (M) B cells. (Left panels) Within the B220-positive fraction, T1 cells are CD24⁺CD21⁻, T2 are CD24⁺CD21⁺, and mature B cells are CD24^lowCD21^low. (Right panels) Within the B220-positive fraction, T1 cells are IgM^highIgD^low, T2 cells are IgM^highIgD^high, and mature B cells are IgM^lowIgD^high/B220⁺. The number of cells present in each fraction is presented as relative percentage of the total cell number plotted. Data are representative of 4 independent experiments (each experiment consisted of 1 vehicle-treated Ptch^flox/floxERT2^+/−, 1 tamoxifen-treated Ptch^flox/floxERT2^−/−, and 1 tPtch^−/− mouse).