Infant Gut Bacteria May Reveal Asthma and Allergy Risk

Infants who have unusual immunoglobulin A (IgA) patterns in their gut microbiota tend to become children with asthma and allergies, according to the results of a recent study. Majda Dzidic, MSc, of the Department of Clinical and Experimental Medicine at Linkoping University in Sweden authored the study, along with colleagues.

The authors objective when they began the study was to characterize the dominant bacteria and to determine what proportion of those bacteria had IgA coating in the context of allergy development, in stool samples of infants. Previous studies have shown that “the gut microbiota differs in composition and diversity during the first months of life in children who later do or do not have allergic disease,” say the authors. However, scientists have not yet determined specific microbes are consistently involved in either the development of disease or in providing protection from disease.

In the present study, the researchers chose to investigate IgA because they theorized that an impaired or reduced mucosal barrier could make allergy development more likely, and IgA is the main mediator of humoral mucosal immunity. Furthermore, IgA is the most abundant antibody in humans, and it is most secreted in the intestines. The authors say, “Secretory IgA (SIgA) has a crucial role in the gut through its binding to bacterial antigens, thus preventing their direct interaction with the host through immune exclusion and maintaining mucosal homeostasis.”

Additionally, it appears that SIgA from breast milk has an important role in immune regulation and protection against various infections in infants. In order to learn more, the researchers used flow cytometry to sort the cells and determine which bacteria were most dominant in the gut and whether or not those cells were IgA coated.

The present study drew participants from a previously conducted study, and included stool samples from 20 children who had developed allergies, 10 of whom had asthma, and 28 children who remained healthy.

On the general level, the researchers report that an important finding of this study is that “the first year of life represents an early critical period in which aberrant gut microbiota IgA responses are linked to the risk of asthma and allergic disease.” SIgA is, according to the authors, “a first line of defense” against asthma and allergy.

More specifically, the researchers found that SIgA limits the overgrowth of certain bacteria, allowing for more diversity of microbiota in the intestinal tract, and such diversity is particularly important for a healthy immune response in childhood. The researchers also note that development of allergic disease, especially asthma, “was associated with a reduced proportion of IgA bound to fecal bacteria at 12 months of age”. They further observed that there was a clear difference in IgA index patterns between healthy children and those with allergic symptoms as early as 1 month of age.

In infants who are exclusively breastfed, IgA is derived mostly from breast milk, leading the authors to say, “the divergent responses observed at this time suggest that immunologic interactions between mother and offspring influence allergy development,” adding that this finding is in line with those of previous studies.

The authors conclude by saying that IgA responses could be helpful in determining what the development of normal mucosal immunity looks like, as well as in what ways maternal immunity may affect the process. The full study, titled “Aberrant IgA Responses to the Gut Microbiota During Infancy Precede Asthma and Allergy Development” was published online in August 2016, and is currently in print in the Journal of Allergy and Clinical Immunology.

Related Coverage:

Role of Gut Bacteria in Asthma and Allergic Disease Becoming Clearer

Infants’ Risk of Asthma Depends on Gut Microbiome

Paternal Tobacco Use Raises Asthma Risk in Offspring, Even Years Before Conception