One of the well-known features of human milk, is the capacity to protect against the risk and impact of neonatal infections, as well as to influence the onset of allergic and metabolic disease manifestations. The major objective of this review is to provide a detailed overview regarding the role of human milk, more specifically the diversity in human milk oligosaccharides (HMOS), on early life immune development. Novel insights in immune modulatory effects of HMOS obtained by in vitro as well as in vivo studies, adds to the understanding on how early life nutrition may impact immune development. Extensive description and analysis of single HMOS contributing to the diversity within the composition provided during breastfeeding will be discussed with specific emphasis on immune development and the susceptibility to neonatal and childhood infections.

The development of infant gut microbiota is strongly influenced by nutrition. Human milk oligosaccharides (HMOSs) in breast milk selectively promote the growth of glycan-degrading microbes, which lays the basis of the microbial network. In this study, we investigated the trophic interaction between Bacteroides thetaiotaomicron and the butyrate-producing Anaerostipes caccae in the presence of early-life carbohydrates. Anaerobic bioreactors were set up to study the monocultures of B. thetaiotaomicron and the co-cultures of B. thetaiotaomicron with A. caccae in minimal media supplemented with lactose or a total human milk carbohydrate fraction. Bacterial growth (qPCR), metabolites (HPLC), and HMOS utilization (LC-ESI-MS²) were monitored. B. thetaiotaomicron displayed potent glycan catabolic capability with differential preference in degrading specific low molecular weight HMOSs, including the neutral trioses (2′-FL and 3-FL), neutral tetraoses (DFL, LNT, LNnT), neutral pentaoses (LNFP I, II, III, V), and acidic trioses (3′-SL and 6′-SL). In contrast, A. caccae was not able to utilize lactose and HMOSs. However, the signature metabolite of A. caccae, butyrate, was detected in co-culture with B. thetaiotaomicron. As such, A. caccae cross-fed on B. thetaiotaomicron-derived monosaccharides, acetate, and d-lactate for growth and concomitant butyrate production. This study provides a proof of concept that B. thetaiotaomicron could drive the butyrogenic metabolic network in the infant gut.

Gangliosides are considered bioactive components in human infant nutrition, and their fatty acid composition alters their biological effects. We used matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) MS and GLC to analyze the fatty acid composition of the predominant gangliosides, the monosialoganglioside GM₃ [sialic acid (Sia) α2–3 galactose (Gal) β1–4 glucose (Glc) β1–1 ceramide] and the disialoganglioside GD₃ (Sia α2–8 Sia α2–3 Gal β1–4 Glc β1–1 ceramide), in pooled human and bovine milk, the latter being a source for gangliosides in infant formula. Compared with whole milk lipids, both human and bovine milk gangliosides were selectively enriched with certain fatty acids, and the fatty acid composition of milk gangliosides in the 2 species was significantly different. The amount of long-chain fatty acids (≥20 C atoms) was higher in bovine milk gangliosides (GM₃: 73.71 ± 3.39%; GD₃: 79.19 ± 2.79%) than in human milk gangliosides (GM₃: 51.25 ± 0.65%; GD₃: 34.04 ± 1.80%). Tricosanoic acid (23:0) dominated in bovine milk gangliosides (GM₃: 24.05 ± 1.37%; GD₃: 26.66 ± 1.24%), whereas it only played a minor role in human milk gangliosides (GM₃: 2.88 ± 0.10%; GD₃: 1.84 ± 0.29%). We hypothesized that the differences in the fatty acid composition of milk gangliosides result in physiological distinctions between breast-fed and formula-fed infants and therefore are of importance for human infant nutrition.

Human milk oligosaccharides (HMOs) have specific dose-dependent effects on child health outcomes. The HMO profile differs across mothers and is largely dependent on gene expression of specific transferase enzymes in the lactocytes. This study investigated the trajectories of absolute HMO concentrations at three time points during lactation, using a more accurate, robust, and extensively validated method for HMO quantification. We analyzed human milk sampled at 6 weeks (n = 682), 6 months (n = 448), and 12 months (n = 73) of lactation in a birth cohort study conducted in south Germany, using label-free targeted liquid chromatography mass spectrometry (LC-MS²). We assessed trajectories of HMO concentrations over time and used linear mixed models to explore the effect of secretor status and milk group on these trajectories. Generalized linear model-based analysis was used to examine associations between HMOs measured at 6 weeks of lactation and maternal characteristics. Results: Overall, 74%, 18%, 7%, and 1% of human milk samples were attributed to milk groups I, II, III, and IV, respectively. Most HMO concentrations declined over lactation, but some increased. Cross-sectionally, HMOs presented high variations within milk groups and secretor groups. The trajectories of HMO concentrations during lactation were largely attributed to the milk group and secretor status. None of the other maternal characteristics were associated with the HMO concentrations. The observed changes in the HMO concentrations at different time points during lactation and variations of HMOs between milk groups warrant further investigation of their potential impact on child health outcomes. These results will aid in the evaluation and determination of adequate nutrient intakes, as well as further (or future) investigation of the dose-dependent impact of these biological components on infant and child health outcomes.