Purpose: To investigate the effects of low dose endotoxin on transcriptional activity in intestinal epithelium, and its role in necrotizing enterocolitis (NEC). Methods: Lipopolysaccharides (LPS) were injected into the amniotic cavity of pregnant mice under ultrasound guidance. The effects of LPS on fetal and neonatal intestines were determined. Mouse pups were exposed to low dose LPS (0.01 mu g per fetus) prenatally and subjected to experimental NEC after birth. The incidence and severity of NEC, as well as intestinal permeability, NF-kappa B activation, and IL-6 expression were studied. The signaling pathways in the intestinal epithelial cells (IECs) that were activated by LPS were also investigated. Results: Low dose LPS did not increase apoptosis, myeloperoxidase activity, histological injury or NF-kappa B activity in fetal intestines. However, prenatal low dose LPS exposure disturbed the transient and self-limited activation of NF-kappa B in neonatal intestines after birth. Importantly, it increased the incidence and severity of experimental NEC in neonatal mice. In primary IECs, low dose LPS induced IRAK-1 expression via activation of GSK3 beta. Elevated IRAK-1 levels prolonged the activation of IECs upon stimulation by high dose LPS. Conclusion: Prenatal low dose endotoxin exposure disturbs self-limited postnatal epithelial cell activation and predisposes the neonatal intestine to NEC. Level of evidence: Not applicable (experimental animal study). (c) 2020 Elsevier Inc. All rights reserved.