B-cell lymphopoiesis in aging is regulated by IGF-1. (A) Sera collected from the indicated mice were analyzed for IGF-1 by enzyme-linked immunosorbent assay (ELISA). Shown are results for individual mice and group means (n = 5 for each group). (B) IL-7–driven BM cultures were prepared, replacing the FCS in media with 1% serum from young mice in the presence or absence of goat–anti-mouse IGF-1 (50 ng/mL). After 5 days, cells were harvested, counted, and stained to quantify B-cell numbers. Graph depicts mean from 4 experiments ± SE. (C-F) Old mice were subcutaneously injected with human GH (hGH) (C-D) or with human IGF-1 (hIGF-1) (E-F) for 10 days. Control mice were injected with phosphate-buffered saline (PBS). One day after the last injection, we analyzed the BM of the mice for B-cell lymphopoiesis (described in the Figure 2 legend) with gates marked for pro-B , pre-B, and immature B cells. Shown are representative plots for a single mouse from each group (C,E) and absolute cell numbers (D,F) for pro-B , pre-B, and immature B-cell populations. Graphs depict means from 5 mice in each group ± SE (in 2 different experiments). Reference values for pro-B , pre-B, and immature B cell numbers in young mice are shown in Figure 2. (G-H) IL-7–driven BM cultures containing 1% fresh serum from young or old mice in the absence or presence of hIGF-1 were prepared. After 5 days, cells were harvested, counted, and stained to quantify B-cell numbers. Shown are representative results from a single experiment (G) and absolute B-cell counts (H) in the cultures. Graph depicts mean from 4 experiments ± SE.