Impairment of B-cell development in the absence of STAT3 is cell autonomous. BM of control (▪) or STAT3KO (□) mice was intravenously transplanted into lethally irradiated RAG1KO mice for 2 months. Total cell extracts prepared from BM (A) or spleen (E) were subjected to immunoblot using antibodies to STAT3 or β-actin. BM cells of chimeric mice were stained with anti-CD43, anti-IgM, and anti-B220 antibodies, followed by FACS analysis. Percentage (B) and cellularity (C) of reconstituted B-cell lineages were determined. (D) Similarly, splenocytes of control→RAG1KO (left panel) or STAT3→RAG1KO (right panel) chimeric mice were isolated after transplantation and were stained with anti-IgM and anti-IgD followed by FACS analysis. Percentages of T1 and T2+MB are shown. Percentage (F) and cellularity (G-H) are shown. IgM^high IgD^low represent T1 cells. IgM^{intermediate-high} IgD^high represent T2 or mature B (MB) cells. Results are presented as mean ± SE of replicate samples.