Decreased numbers of B-cell precursors in the bone marrow and mature B cells in the blood of Stat5-deficient mice.

(A, B) FACS analysis of fresh bone marrow isolated from Stat5 (+/−) and Stat5 (−/−) mice. Data represent percent of IgM-negative lymphoid populations. B220 and CD43 staining allows the distinction in B-cell precursor subsets. (C) Peripheral blood was withdrawn from 3-month-old Stat5-deficient mice and their heterozygous littermates. Absolute numbers of B220-positive cells per microliter are shown. (D) B220-positive, Thy1.2-negative cells were sorted by FACS, plated in 96-well round bottom dishes and stimulated as indicated. 48 hours after stimulation, [³H]-thymidine was added. Thymidine incorporation in heterozygous cells (■) and in Stat5-deficient cells (▨) is shown. (E) Determination of the antibody response to the T-cell–dependent antigen ovalbumin. Ovalbumin-specific serum IgM and IgG1 titration curves are shown. Each dilution curve represents the average of 5 mice. ■, heterozygous mice; ▪, Stat5a/b-deficient mice. (F) measurement of the serum IgM response against the T-cell–independent antigen NP-Ficoll. Results are the average of 5 mice. Preimmunization titers, ▪; postimmunization titers, ▨.