Allergic diseases affect millions of people worldwide, and are on the rise. An increase in the prevalence of these diseases has been associated with alterations in the gut microbiome, i.e., the microorganisms within the gastrointestinal tract. Maturation of the infant immune system and gut microbiota occur in parallel; thus, the normal development of the microbiome likely determines tolerant immune programming in the infant. Antigens are substances that can produce an immune response, and tolerant immune programming is a mechanism of immune tolerance where the self-antigen is protected from the immune system’s destructive response. Thus the immune system is programmed to be destructive against non-self-antigens (bacteria and viruses contain non-delf antigens, for example), but not self antigens. 

A new study reported that a trend in maturation alteration is characterized by depletions in the bacterial species A. hadrus, F. saccharivorans, E. hallii, and B. wexlerae in participants who later developed allergic diseases, as well as enrichments in E. lenta, C. innocuum, E. faecalis, E. coli, and T. nexilis in these participants. The depleted bacterial populations are known short-chain fatty acid (SCFA) producers, notably the butyrate producers A. hadrus, E. hallii, and F. saccharivorans and the acetate producer B. wexlerae; SCFAs are metabolites that mediate well-defined host benefits within the gut. The authors also reported a depletion of butyrate in allergy-prone participants and significant associations between A. hadrus and F. saccharivorans respective relative abundance and butyrate concentration. This strengthens the postulation that the production of butyrate and its effect on immune cells is a mode by which optimal immune modulation occurs during early life. In contrast, species enriched in allergy-prone participants have been linked to pathogenic activity and poor health outcomes, with many of these microbiome features associating with metabolites enriched within these same participants.

Most diseases are consequence of our exposome, and not hereditary genetic factors. Our exposome greatly affects our microbiome. Established primarily during infancy, the developing microbiota’s initial expansion and fluctuation are particularly sensitive to external influences before reaching a more stable community. Sensitivity of the microbiome is most pronounced during infancy, and abnormal exposures, such as that in a hospital setting, especially during a C-section, that can drastically alter the microbiome. The number of C-Sections in 2015 doubled in comparison to those registered in 2000, and jurisdictions such as California have instituted programs to stop the medical practice of performing unneeded C-sections. Indeed, many risk factors for allergic diseases, including mode of delivery, diet, urban living, and antibiotic exposure (such as the overprescribed broad spectrum antibiotic Amoxicillin), also influence early microbiota membership and structure. Note: the broad spectrum antibiotics are particularly harmful because the drug kills so many beneficial types of bacteria. While this maturation process usually coincides with the development of healthy immune tolerance, allergic sensitization can emerge in many children because of their exposome during the same period as the microbiota is being established.

Overall, the authors compared 1115 children with asthma, allergic rhinitis, food allergy, or Eczema (atopic dermatitis) to a rigorously defined, non-allergic comparator group. They described detailed underpinnings driving this decrease in gut microbiome maturation, encompassed within the alteration of a core group of bacterial species, functional pathways (i.e., potential intestinal mucous integrity breakdown, elevated oxidative stress levels, and subsequently oxidized monosaccharides, and diminished secondary fermentation), and metabolic imbalance i.e., elevated trace amines that can be involved in inflammation and neural function, and associated with reduced microbiota-maturation age and elevated risk of allergy.

Bottom line, the infant exposome is critical for the development of a normal microbiome and a life without allergy and skin conditions without Eczema.