Heme oxygenase-1 confers protection and alters T-cell populations in a mouse model of neonatal intestinal inflammation

BACKGROUND: Necrotizing enterocolitis (NEC), an intestinal inflammatory disease affecting premature infants, is associated with low regulatory T (Treg) to effector T (Teff) cell ratios. We recently demonstrated that heme oxygenase-1 (HO-1) deficiency leads to increased NEC development. Here, we investigated the effects of HO-1 on T-cell proportions in a murine NEC-like injury model. METHODS: Intestinal injury was induced in 7-d-old wildtype (WT) or HO-1 heterozygous (HO-1 Het) pups by formula-feeding every 4h for 24-78h by oral gavage and exposures to 5%O-2. Controls remained breastfed. HO-1 was induced in WT pups by administering heme preinjury induction. Lamina propria T cells were identified by flow cytometry. For adoptive transfer studies, WT splenic/thymic Tregs were injected intraperitoneally into HO-1 Het pups 12-24 h preinduction. Results: Het mice showed increased intestinal injury and decreased Treg/Teff ratios. Genes for pattern recognition (Toll-like receptor-4, C-reactive protein, MyD88) and neutrophil recruitment increased in Het pups after NEC induction. Inducing intestinal HO-1 decreased NEC scores and incidence, and increased Treg/Teff ratios. Moreover, adoptive transfer of Tregs from WT to HO-1 Het pups decreased NEC scores and incidence and restored Treg/Teff ratios. Conclusion: HO-1 can change Treg proportions in the lamina propria of young mice under inflammatory conditions, which might, in part, confer intestinal protection