a, Flow cytometry analysis of aged neutrophils in control, antibiotics (ABX)-treated mice and ABX-treated mice fed with LPS (n = 12,7,5 mice). b, Numbers of aged neutrophils in specific pathogen free (SPF) mice, Germ-free (GF) mice, GF mice reconstituted by fecal transplantation (GF-FT), and GF mice treated with antibiotics (GF-ABX; n = 5,5,5,3 mice). c, Ageing kinetics of donor neutrophils after adoptive transfer into control, ABX-treated or GF recipients (n = 4 mice). d, EdU pulse-chase analysis of neutrophil release-clearance kinetics in control and ABX-treated mice (Ctrl: n = 5,5,6,8,5 mice; ABX: n = 5,5,5,6,6 mice for day 3,4,5,6,7). e–g, Representative images (e) and quantification of neutrophil adhesion (dotted lines; f) and Mac-1 activation on adherent neutrophils (g) in control and ABX-treated mice (n = 4 mice). Scale bar, 10 μm. Error bars, mean ± s.e.m. * P < 0.05, ** P < 0.01, *** P < 0.001, data representing ≥2 independent experiments analysed with unpaired Student’s t-test.