B-cell development in TC-PTP^+/+ and TC-PTP^−/− bone marrow. Whole bone marrow was harvested from TC-PTP^+/+ (WT) and TC-PTP^−/− (KO) mice at P1 (3 WT, 3 KO), P3 (3 WT, 3 KO), P4 (4 WT, 4 KO), and P7 (11 WT, 6 KO). (A) Cells were stained for flow cytometry and analysis was gated on B220⁺ cells to include only B cells (∼20% B220⁺ at P1, P3 and ∼25% B220⁺ at P4, P7). Representative data are shown for each time point. The percentage of each subpopulation is shown in the upper right quadrant. (B) Absolute cell counts for each B-cell subset from TC-PTP^+/+ (□) and TC-PTP^−/− (▪) are illustrated. Cell counts were derived by multiplying the percentage of total cells, obtained by flow cytometry for each subpopulation, by the whole marrow cell count, obtained by manual counting with a hemocytometer. Cell counts are reported as mean ± SD. *P < .01. (C) Whole bone marrow was harvested from TC-PTP^+/+ (WT) and TC-PTP^−/− (KO) mice at P7 (5 WT, 5 KO). Cells (1 × 10⁶) were stained for surface expression of CD25, CD43, and B220, and with annexin V and propidium iodide (PI), and analyzed by flow cytometry. Analysis was gated on B220⁺ cells to include only B cells. The combined percentage of preapoptotic (annexin V⁺, PI⁻) and apoptotic (annexin V⁺, PI⁺) cells is provided. Representative data are shown for each subset. All experiments were repeated at least 3 times.