Gut Microbiome, Allergies

The “hygiene hypothesis” suggests that the increase in allergic and autoimmune diseases such as asthma, allergic rhinitis (hayfever), and multiple sclerosis in developed countries is linked to a decline in infectious burden that causes an immune imbalance. One particular theory is that certain infectious agents that co-evolved with us, including probiotics such as Lactobacillus, are protective against the development of allergic disease. New research into the infant gut microbiome and the development of childhood allergies adds weight to this theory. In a study published online in the Journal of Allergy and Clinical Immunology, Dr. Hans Bisgaard and colleagues show that infants with a less diverse gut microbiome have an increased risk of developing allergic sensitization and allergic rhinitis as they grow up.

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In the study Dr. Bisgaard and colleagues used 16S rRNA PCR and conventional culturing to identify the fecal bacteria present in 253 infants. Samples were taken when the children were 1 month and 12 months old and the children were then monitored every 6 months until they were 6 years old. In addition to the fecal bacterial analysis IgE levels in response to a panel of allergens were assessed as was the response to a skin prick test for the same allergens and the levels of peripheral blood eosinophils. When the children reached 6 years old the presence or absence of allergic rhinitis, asthma, and atopic dermatitis was identified.

The analysis of fecal bacteria showed that the diversity of the gut microbiome increases between 1 month and 12 months of age. In particular the prevalence of enterobacteriaceae, enterococcaceae, yeast, and fungi increased but the abundance of staphylococcaceae decreased. The level of diversity present was inversely associated with the development of sensitization as measured by serum IgE levels, skin prick test results, peripheral blood eosinophilia, and the presence of allergic rhinitis at 6 years of age. There was, however, no increase in the risk of asthma or atopic dermatitis at the age of 6, possibly indicating differences in the mechanisms of development of these two conditions.

Interestingly, sensitization as measured by IgE levels was associated with the presence of staphylococcaceae at 1 month but not at 12 months and no other single bacterial genera was implicated in the development of allergic sensitization. This suggests that having a diverse range of microbiota in the gut is more important than the presence or absence of a particular bacterial strain. The next step in this research is to identify the mechanisms by which the gut microbiome influences the development of allergic responses.

About the author: Ruth Warre is a freelance scientific writer and editor currently living in Toronto. She writes on a variety of subjects from microbiomes to neuroscience, in a variety of mediums from blogs to peer-reviewed articles.

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