Colonization of mice lungs by microbes shortly after birth helps protect them from developing asthma in adulthood, according to a study published this week in Nature Medicine. These findings highlight the influence of environmental factors early in life on the appropriate development and maturation of the immune system.

Although the lungs are sterile at birth, they progressively are colonized by microbes. Whether this event alters immune cell development or susceptibility to disease later in life remains unclear.

Benjamin J Marsland and colleagues show that newborn mice were prone to develop airway disease, including inflammation in the lungs, when challenged with an allergen, but were later tolerant to the allergen and did not develop disease as adults. Over the course of two months, the lungs were colonized by microbes, which led to the development of a subset of immune cells that are anti-inflammatory and can suppress airway disease and asthma. Keeping mice in sterile conditions to prevent this colonization rendered these mice sensitive to allergens and resulted in airway disease as adults. This research uncovers a developmental window early in life during which colonization of the lung by microbes influences immune cell development and supports epidemiological data on the protective role of certain microbes in neonates.