The findings – published in the Journal of Allergy and Clinical Immunology – report that diversity of the gut ecosystem, rather than the presence of certain strains of bacteria, is essential in protecting against allergies.
The researchers, from the Linköping University in Sweden, studied the intestinal microflora in allergic and healthy children, to test whether they could find evidence to back up the so called ‘hygiene hypothesis.’
This hypothesis is based on the idea that our immune system encounters too few bacteria during childhood, thus explaining the increasing proportion of allergic children.
"Children acquire intestinal microflora from their environment, and in our society they are probably exposed to insufficient bacteria that are necessary for the immune system to mature," said Dr Thomas Abrahamsson of Linköping University – the first author of the study.
The hygiene hypothesis states that a lack of early childhood exposure to infectious agents, symbiotic microorganisms (such as probiotics or those found in gut flora), and parasites increases susceptibility to allergic diseases by suppressing natural development of the immune system.
The rising level of allergies and autoimmune diseases seen in young people has been seen as evidence to suggest a basis for this theory. However, it has been difficult to substantiate the premise scientifically.
Abrahamsson and his team noted that researchers previously believed diversity and variability -microbial diversity - is significant for allergy development in infants. However, not until now, could a clear connection be established – thanks to new developments in DNA-based technologies.
The research team analysed stool samples from 40 children: 20 with atopic eczema and allergic IgE antibodies to foods, and another 20 in a control group with no conditions.
Used genetic sequencing techniques the team then identified the DNA of bacteria present in the guts of the children.
Microflora diversity was found to be significantly greater in healthy children at one month of age compared to those children who later developed allergies.
The team added that diversity in certain groups also appears to be particularly important, whilst others appeared to show no benefit. They said that Proteobacteria were found to be associated with protection against allergies, whilst Bacteroides were shown to counteract inflammation.
However, the results of other studies – such as those supporting a role for Bifidobacteria – appear to be called in to question, they suggested.
One example is Bifidobacteria that used as a supplement in dairy products.
Abrahamsson and his team noted that although Bifidobacteria were abundant in the study, they could not identify support for any protective effect. Instead they said that it is the overall composition of intestinal microflora during the first weeks of life that show signs of being critical to the immune system's development.
In the absence of sufficient stimuli from many different bacteria, the system may overreact against harmless antigens in the environment, such as foods, they suggested.
Source: Journal of Allergy and Clinical Immunology
Published online ahead of print, doi: 10.1016/j.jaci.2011.10.025
“Low diversity of the gut microbiota in infants with atopic eczema”
Authors: T.R. Abrahamsson, H.E. Jakobsson, A.F. Andersson, B. Björkstén, L. Engstrand, M.C. Jenmalm