Microbiota-derived bDNA is systemically circulating and sensed by BM CX3CR1⁺ MNCs. (A) Reverse-transcription quantitative polymerase chain reaction analysis of bacterial 16S ribosomal RNA (rRNA) in the BM of SPF, GF, and CoH-GF mice (n = 8-11). (B) Quantification of bacterial 16S rRNA in lineage cells of the BM in SPF mice, with cells pooled from 3 mice per group. (C) Composition of bacterial phylum of CX3CR1⁺ MNCs in the BM from WT SPF mice. Quantification of bacterial 16S rRNA in lineage cells from BM of Myd88^−/− (D) and 3d mice (G) vs 16S rRNA in BM of GF mice as control (n = 3). Quantification of inflammatory cytokines in the mRNA (E,H; n = 3 or 4 mice) and protein (F [n = 4 or 5 mice] and I [n = 6-8 mice]) from Myd88^−/− mice (E-F) and 3d mice (H-I) in comparison with their WT controls. mRNA level of each cytokine was measured in the CX3CR1⁺ MNCs of each group of mice by reverse-transcription quantitative polymerase chain reaction (pooled samples from 3 or 4 mice per group), and protein was measured in the BM lavage fluids by enzyme-linked immunosorbent assay. Data are representative of 2 (A-B,D-E,G-H) or 3 (F,I) independent experiments with similar results. Data are mean ± standard error of the mean. *CX3CR1⁺ MNCs vs other cell types. ^#Each cell type vs GF_BM control. Each circle represents an individual mouse. *^/#P < .05, **^/##P < .01, ***^/###P < .001, unpaired 2-tailed Student t test (E-F,H-I), 1-way ANOVA with Bonferroni multiple comparison (B,D,G), 1-way ANOVA with Newman-Keuls’ multiple comparison (A). N.S., not significant; U.D., undetermined.