Investigating the immune system of extremely preterm infants and the effect of diet

Abstract

Extremely preterm infants are susceptible to life-threatening diseases, specifically late onset sepsis (LOS) and necrotising enterocolitis (NEC). Both these diseases are associated with changes in the gut microbiota and an immature immune response. Mother’s own milk (MOM) has been shown to reduce the incidence of both NEC and LOS. When MOM is not available, the alternatives are donor human milk (DHM) or cow’s milk formula (CMF). Clinical trials have shown an inconsistent effect on rates of NEC or LOS when DHM is used instead of CMF to make up any shortfall of MOM, although the use of DHM or CMF as sole diet tends to favour DHM. Inconsistencies or lack of effect could be due to differences in the concentration of bioactive components of DHM compared to MOM, as DHM is usually from donors who are longer post-partum, and is usually pasteurised and frozen. The diet of preterm infants affects both their gut microbiota and gut mucosal T cells, which may be instrumental to any impact on LOS and NEC. This study aimed to identify differences in gut microbial or T cell composition if infants were fed an exclusively human milk (MOM+/-DHM) diet (Intervention) compared to a diet containing bovine products (MOM+/-CMF) (Control). The hypothesis was that an exclusively human milk diet would be associated with changes in microbial diversity, abundance of Bifidobacteria, Regulatory T cells, Mucosa-associated invariant T cells and invariant natural killer T cells. Infants of less than 30 weeks gestational age (GA) were recruited to a randomised controlled trial comparing the two diets until 34 weeks GA. Stool samples were taken throughout the trial period, which were analysed using 16S rRNA sequencing at 5 time-points, and blood samples taken at 2 time-points were analysed using mass cytometry. This report provides data from a pilot study of 59 infants. Infants in the intervention group paradoxically received less MOM overall and had decreased rate of growth (weight). There was a significant difference in unweighted microbial beta-diversity at 34 weeks GA and a significantly increased abundance of lactobacillus at 34 weeks GA in the control group. There was no difference in T cell populations between the trial populations, however clear differences were noted when compared to adult control samples. In conclusion, an exclusively human milk diet did not result in measurable changes in gut bacterial community structure or changes in T cell immunophenotype when compared to a diet containing bovine products. However, the routine use of supplemental probiotics containing Bifidobacteria and Lactobacillus in this study population may mask important effects