Although Smad1/5/8 signaling is not activated by inflammatory stimuli in the absence of activin B, this has no impact on the induction of hepcidin expression. (A-B) Fresh protein extracts were prepared from livers of wild-type (WT) and activin B (Inhbb)–deficient mice 4 hours after a LPS challenge or infection with E coli. Phospho-Smad2, phospho-Smad5, phospho-Stat3, total Smad2, total Smad5, and total Stat3 were detected by immunoblot techniques on a Chemidoc MP Imaging System (Bio-Rad). (C-F) Evolution over time of activin B (Inhbb) (C-D) and hepcidin (Hamp) (E-F) mRNA expression was examined in wild-type mice and (for hepcidin) Inhbb^−/− mice challenged with LPS or infected with E coli. Point estimates of the fold change (FC) in gene expression relative to baseline (2^−ΔΔCt) are shown on the graphs, together with their 95% confidence intervals (CIs). When the lower limit of the fold-change CI exceeds 1, gene expression is significantly induced relative to baseline. (G) Serum hepcidin levels were measured by competitive ELISA in wild-type and Inhbb^−/− mice at baseline and 4 hours after LPS challenge. Values shown are geometric means ± 95% CIs. Comparisons of log-transformed serum hepcidin levels were made by 2-way analysis of variance followed by Sidak’s multiple comparison tests of planned contrasts. Results of comparisons with baseline levels in mice of the same genotype are shown above the bars. ****P < .0001.