High intestinal microbial diversity safeguards against allergies, study suggests

One hypothesis is that our immune system encounters too few bacteria during childhood, which explains the increasing proportion of allergic children. However it has been difficult to substantiate the hypothesis scientifically.

"We conducted the study in collaboration with Karolinska Institute and the KTH Royal Institute of Technology which substantiates the so-called hygiene hypothesis. 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," says Thomas Abrahamsson, paediatric physician and a researcher at Linköping University.

Abrahamsson is the lead author of the study recently published in the Journal of Allergy and Clinical Immunology.

Researchers previously believed that diversity and variability -microbial diversity -- is significant for allergy development in infants. However, not until now, can a clear connection be established due to the latest DNA-based technologies. Employing these cogent methods enables a complete overhaul of the microbiological framework.

Stool samples from 40 children were analysed: 20 children with atopic eczema and allergic IgE antibodies to foods, and another 20 in a control group that lacked these conditions. Using the so-called 454-pyrosequencing, the researchers identified DNA sequences that were then simultaneously linked with a database to determine which bacterial genera was present in the samples.

The results show that diversity was significantly greater in the healthy children at one month of age compared to those children who later developed allergies. Diversity in certain groups appears to be particularly important: Proteobacteria consists of so-called gram-negative bacteria which are associated with protection against allergies and are common in children who grew up on livestock farms with cattle, and even Bacteroides which as shown in the experiments counteract inflammation.

Meanwhile, the results of other studies would appear to be discredited.

One example is Bifidobacteria that used as a supplement in dairy products. They were abundant in the study however the researchers could not identify support for any protective effect.

It is the 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. The risk of developing asthma at school age for children afflicted by these allergies is five to six times higher.