Impaired development of different B lineages in the BM of STAT3KO mice. BM cells of control (•) or STAT3KO (○) mice were stained with anti-B220, anti-CD43, anti-IgM, and anti-IgD antibodies, then FACS analysis was performed. (A) Reduced percentages of pro-B (B220⁺CD43⁺IgM^–), pre-B (B220⁺CD43^–IgM^–), immature B (IMB; B220⁺ CD43^–IgM⁺), and mature B (MB; IgD⁺IgM⁺) in the BM of STAT3KO mice. (B) Reduced numbers of pro-B, pre-B, IMB, and MB in the BM of STAT3KO mice. Numbers were calculated from the total number of BM multiplied by the percentage of corresponding B lineages. (C) Accumulation of pre–pro-B cells in the BM of STAT3KO mice. BM cells of control (•) and STAT3KO (○) mice were 4-color stained with anti-CD43, anti-B220, anti–BP-1, and anti-CD24, followed by FACS analysis. Individual percentages of fraction A (CD43⁺B220⁺BP-1^–CD24^– or pre-pro B), fraction B (CD43⁺B220⁺BP-1^–CD24⁺ or early pro-B), and fraction C (CD43⁺B220⁺BP-1⁺CD24⁺ or late pro-B) are indicated. *P < .05; Student t test (control mice, n = 7; STAT3KO mice, n = 4). Horizontal bars indicate the mean value for each group.