Urbanized microbiota in infants, immune constitution and later risk of atopic diseases

Urbanization is linked with an increased burden of asthma and atopic traits. A putative mechanism is insufficient exposure to beneficial microbes early in life leading to immune dysregulation as previously shown for indoor microbial exposures. To investigate whether urbanization is associated with the microbiota composition in the infants' body and early immune function, and whether these contribute to the later risk of asthma and atopic traits.

We studied the prospective COPSAC2010 mother-child cohort of 700 children growing up in areas with different degrees of urbanization. During their first year of life, airway and gut microbiota as well as immune marker concentrations were defined. At six years of age, asthma and atopic traits were diagnosed by pediatricians.

In adjusted analyses, the risk of asthma and aeroallergen sensitization were increased in urban infants. The composition of especially airway, but also gut microbiota differed between urban and rural infants. The living environment related structure of the airway microbiota associated with immune mediator concentrations already at one month of age.

An urbanized structure of airway and gut microbiota associated with an increased risk of asthma coherently during multiple time points, and also with the risks of eczema and sensitization. Our findings suggest that urbanization related changes in the infant microbiota may elevate the risk of asthma and atopic traits, probably via crosstalk with the developing immune system.

The airways may facilitate this effect as they are open for colonization by environmental, airborne microbes and serve as immune interface.