Fig. 4. Bacterial putrescine regulates the development of macrophage subsets.

CX₃CR1 and Ly6C expression were analysed in CD45⁺CD11b⁺F4/80⁺ cells via flow cytometry. Representative flow cytometry images (a), frequency (b), number (c) of CX₃CR1^lowLy6C⁺ monocyte/macrophage and CX₃CR1^highLy6C⁻ macrophages and representative flow cytometry images (d), frequency (e), number (f) of NOS2⁺Arg1⁻ and NOS2⁻Arg1⁺ macrophages and the ratio of the former to the latter subset (g) in cLP of gnotobiotic mice colonised with WT (n = 7) or SK930 (n = 8) strain and GF mice (n = 6). CX₃CR1 and Ly6C expression in CD45⁺CD11c⁻CD11b⁺F4/80⁺cells from BMDMs cultured in medium with or without putrescine (n = 4). Representative flow cytometry images (h) and frequency (i). j, k Isotope ratio of putrescine and spermidine in BMDMs cultured with isotope-labelled ¹⁵N₂-putrescine were analysed via GC-MS. The black bar indicates the percent putrescine (PUT) or spermidine (SPD) of ¹⁵N₂-putrescine or ¹⁵N₂-spermidine enrichment in total corresponding polyamines, respectively (n = 3, independent cultures). All data shown represent the mean ± SEM. Kruskal-Wallis followed by Steel-Dwass post hoc test (b–g) and Student’s t-test (i) (two-sided).