Microbiota-induced inflammatory cytokines expand hematopoietic progenitors. (A) Reverse-transcription quantitative polymerase chain reaction analysis of mRNA expression levels of the indicated inflammatory cytokines in the BM cells of SPF and GF mice (n = 8-10). (B) Quantification of TNF-α, IL-1β, and IL-6 by enzyme-linked immunosorbent assay of the BM lavage fluids from SPF, GF, and CoH-GF mice (n = 8–10). (C) Numbers of HSPCs (n = 10) and lineage cells (n = 8) in the BM of SPF mice injected with a cocktail of neutralizing antibodies against TNF-α, IL-1β, and IL-6. (D) Flow cytometry of cytokine receptor expression by HSPCs of SPF mice. Concatenated graphs of each cell type from 3 or 4 mice. Data are representative of 2 or 3 independent experiments (A-B,D) and are pooled from 2 independent experiments (C). Data are mean ± standard error of the mean, and each circle represents an individual mouse. *P < .05, **P < .01, ***P < .001, unpaired 2-tailed Student t test (A,C) or 1-way ANOVA with Bonferroni multiple comparison (B). IL-1R, IL-1 receptor; IL-6R, IL-6 receptor; TNFR1, TNF receptor 1; TNFR2, TNF receptor 2.