Decreased numbers of B, but not T, cells in the BM and periphery of STAT3KO mice. (A) STAT3 deletion was complete in BM but was partial in the spleens and PBLs. Genomic DNA prepared from BM, spleen (SPN), and peripheral blood (PBL) of control (cre^–) or STAT3KO (cre⁺) mice was subjected to PCR using primers that differentiated deleted allele (STAT3^Δ) and flox allele (STAT3^flox). Total cell extracts prepared from the BM of control or STATKO mice were subjected to immunoblot using antibodies to STAT3 or β-actin (right panels). (B) Decreased numbers of B cells in the periphery. Peripheral blood cells of control (•) or STAT3KO (○) mice were stained with anti-CD3 and anti-CD19, and then FACS analysis for B cells (CD19⁺) or T cells (CD3⁺) was performed. (C) Decreased numbers of mature B cells in the BM and the periphery. BM or PBL of control (•) or STAT3KO (○) mice were stained with anti-IgD and anti-IgM, then FACS analysis was performed. *P < .05; Student t test. Horizontal bars indicate mean values for each group.