Normal B-cell development, but elevated serum IgE in mut-Stat3 mice. (A) Flow cytometry analysis of isolated BM cells from mut-Stat3 and WT mice. Populations were defined as: pro-B [B220lowCD25⁻IgM⁻], pre-B [B220lowCD25⁺IgM⁻], immature (Imm.) [B220lowCD25⁻IgM⁺], and recirculating (Rec.) [B220hiIgM⁺]. Populations are depicted as either percentage of B200 low cells (upper row), or absolute number of cells per BM (lower row). N = 7, not significant (ns): P > .05. Dead cells were excluded from analysis by DAPI staining. (B) ELISA measurement of serum immunoglobulin levels from naïve WT and mut-Stat3 mice aged 8 to 15 weeks (N = 23). (C) Serum Schistosoma mansoni soluble egg antigen–specific immunoglobulin levels were measured by ELISA 3 weeks after peritoneal injections of Serum Schistosoma mansoni soluble egg antigen in WT and mut-Stat3 mice. Shown is a representative result of 3 independent experiments (N = 4 for each experiment).