Healthy gut microflora and allergy: factors influencing development of the microbiota.

In humans, microbial colonization of the intestine begins just after birth. However, development of the normal flora is a gradual process, which is initially determined by factors such as composition of the maternal gut microflora, environment and possibly also by genetic aspects. A number of variables, such as the degree of hygiene, mode of delivery, use of antibiotics or other medication and a need for nursing in incubators, can all have a substantial effect on microbial colonization and development. Current knowledge on the significance and impact of such alterations on the health of the infant is poor. However, the essential role of the gut microflora in the development of the gut immune system indicates that a close relationship between allergic sensitization and the development of the intestinal microflora may occur in infancy. Intestinal micro-organisms could down-regulate the allergic inflammation by counterbalancing type 2 T-helper cell responses and by enhancing antigen exclusion through an immunoglobulin (Ig)A response. The efficacy of probiotics (microbial food additions) in the management of food allergy has been demonstrated, and these data suggest that also prebiotics, food components that target certain indigenous gut bacteria, can possibly be used for this purpose. In conclusion, the developmental pattern of the normal gut microbiota in allergic infants poses an important research avenue, as the role of the gut microflora in the mechanisms of allergy, and thereby the possible targets for efficient bacteriotherapy, are currently undetermined.