Bacteria diversity protects against allergies

Broad diversity and rich variation of intestinal bacteria protects children against allergies, rather than certain individual species of bacterium. This has been shown by a thorough inventory of intestinal flora in children with allergies and healthy children carried out at Linköping University.

One explanation being promoted for the increasing number of children with allergies is that our immune systems encounter too few bacteria during infancy. However it has been difficult to scientifically support this hypothesis.

“The studies we did in cooperation with Karolinska Institutet and the Royal Institute of Technology (KTH)strengthens what we call the hygiene hypothesis. Children get their intestinal flora from their surroundings; in our society they are probably not exposed enough to the bacteria needed for their immune systems to mature, says Thomas Abrahamsson, chief paediatrician and researcher at LiU.

He is the main author of the study, now being published in the highly-ranked Journal of Allergy and Clinical Immunology.

Researchers had previously suspected that diversity was significant for the development of allergies in infants. Only now could a clear connection be established, thanks to new DNA-based technology. The microbiological map is being completely redrawn with such incredibly powerful methods.

Stool samples from 40 children: 20 with atopic dermatitis and IgE antibodies against foodstuffs, and 20 without such symptoms were analysed. Using what’s called 454 pyrosequencing, DNA sequences were identified that were then merged with a database to determine which species of bacterium were found in the samples.

The results show that diversity was significantly greater in healthy children at the age of one month, compared with the children who later developed allergies. The diversity in certain groups, however, appears to be especially important: Proteobacteria, which consist of what are called gram-negative bacteria that were linked to protection against allergies and which are common in children who grew up on farms with livestock, and Bacteroides, which in experiments appeared to counteract inflammation.

At the same time, the results imply that other interpretations appear to be discredited. Bifidobacteria, used as a supplement in dairy products, is one example. They were in abundance in the study, but the researchers found no support for any protective effect.
It is the combination of intestinal flora during the first weeks of life that seem to be important for the immune system maturing. Lacking sufficient stimulation from many different bacteria, the system can overreact to harmless antigens in the environment, for example foodstuffs. Children who suffer from such allergies run five to six times the risk of developing asthma at school age.

Article: Abrahamsson TR, Jakobsson HE, Andersson AF, Björkstén B, Engstrand L, Jenmalm MC:Low diversity of the gut microbiota in infants developing atopic eczema. Journal of Allergy and Clinical Immunology, online 6 December 2011.
Contact: Thomas Abrahamsson, +46 (0) 101 030 000, mobile +46 (0) 709-566 815

Åke Hjelm 2011-12-08