Early immune system development

The neo-natal period is a critical development window for the immune system and many other biological systems, which are driven in part by environmental stimuli, including microbes.
The in utero environment requires that the baby’s immune system is subdued to tolerate maternal alloantigens and the changes and stress involved in development.[1] After birth however, there is a sudden enormous exposure to environmental antigens, many of them derived from intestinal commensal bacteria. This means that the baby’s immune system must adapt quickly to produce immune responses to support early life. Microbes play a critical role in these postnatal immune responses.

Establishing a healthy gut microbiome

The infant microbiota is established immediately at birth when bacteria are transmitted from mother to baby. Research has shown a significant difference between the microbiome of vaginally-delivered and C-section infants. Babies delivered vaginally have been shown to harbour bacteria resembling their own mother’s vaginal microbiota, whilst C-section infants acquire bacteria similar to those found on the skin surface.[2] During the first year of life, the diversity of the bacteria in the microbiota then increases to drive the development of the immune system and ultimately ensure that the bacteria is recognised by the immune system as ‘self’.[3]

Development of the infant gut bacteria

As well as mode of birth, a number of factors have been shown to influence this development, including breastfeeding[4][5] and antibiotic exposure[6].

Breast milk has been shown to be a source of a wide range of bacteria for the infant gut and potentially to be specific for each infant. Interestingly, breast milk has been shown to contain microbes typically associated with the gut.[7]

Antibiotics given, even briefly, during the first year of life have been shown to alter the constitution of the infant microbiota by depleting the bacterial diversity and its ability to colonise the gut.[6] This change to the development of the microbiota is likely to have long-term implications for health[8], as a higher level of beneficial bacteria is associated with lower levels of atopic disease and obesity in children and adults.

Probiotics have been shown to support the development of the infant gut bacteria[9] and specifically to help reduce the incidence of allergy[10] [11]. They may be particularly efficacious in instances where antibiotics have been required.
[1] Simon AK et al (2015) Evolution of the immune system in humans from infancy to old age. Proc R Soc B 282:20143085
[2] Dominguez-Bello MG et al (2010), Delivery mode shapes the acquisition and structure of the initial microbiota across multiple body habitats in newborns. PNAS 107:11971-5
[3] Del Chierico F et al (2015) Phylogenetic and Metabolic Tracking of Gut Microbiota during Perinatal Development. PLOS ONE; DOI:10.1371/journal.pone.0137347
[4] Backhed F et al (2015) Dynamics and stabilization of the human gut microbiome during the first year of life. Cell Host Microbe 17:690-703
[5] Tannock GW et al (2013) Comparison of the compositions of the stool microbiotas of infants fed goat milk formula, cow milk-based formula, or breast milk. Appl Environ Microbiol 79:3040-8
[6] Hussey S et al (2012) Parenteral antibiotics reduce bifidobacteria colonization and diversity in neonates. Int J Microbiol; doi: 10/1155/2011/130574
[7] Murphy K et al (2017) The Composition of Human Milk and Infant Faecal Microbiota Over the First Three Months of Life: A Pilot Study. Sci Rep 7; doi: 10.1038/srep40597
[8] Rodriguez JM et al (2015) The composition of the gut microbiota throughout life, with an emphasis on early life. Microb Ecol Health Dis; 26:26050
[9] Rinne et al (2005) Similar bifidogenic effects of prebiotic-supplemented partially hydrolysed infant formula and breastfeeding on infant gut microbiota. FEMS Immunol Med Microbiol; 43:59-65
[10] Vieira AT et al (2013) The role of probiotics and prebiotics in inducing gut immunity. Front Immunol 4;445
[11] Allen SJ et al (2014) Probiotics in the prevention of eczema: a randomised controlled trial. Arch Dis Child; DOI:10.1136/archdischild-2013-305799

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