Early life antibiotics induce in vivo precocious maturation of the intestinal epithelium. (A) Whole-tissue real-time qPCR analysis of adult maturation markers Sis and Arg2 and of fetal maturation markers FcRn and Ass1 in proximal and distal small intestine. Relative expression to reference genes Cyp and Ppib. Immunohistochemistry of (B) adult marker Sis and (C) fetal marker Ass1 in proximal and distal small intestine. Black triangles indicate positive cells and white triangles indicate negative cells. Scale bars: 100 μm. Statistical analysis was performed by 1-tailed unpaired t test (Sis, FcRn, and Ass1) or Mann–Whitney test because data were not distributed normally when assessed by the D’Agostino and Pearson normality test (Arg2). Error bars indicate means ± SD (Sis, FcRn, and Ass1) or medians with interquartile range (Arg2). Levels of significance are indicated: ∗P < .05, ∗∗P < .01. n = 10–12 pups per group.