Dysbiosis of the intestinal microbiota has been associated with development of allergies in infants.
However, it is not clear what microbes might contribute to this process.
Dr Yen-Hsuan Ni and colleagues from Taiwan investigated what microbe(s) might be involved in analyses of infant twins and mice.
The research team studied fecal specimens prospectively in a twin cohort, and age-matched singletons born at National Taiwan University Children’s Hospital, Taipei, Taiwan, from 2011 to 2013.
The team recorded clinical parameters.
Fecal samples were collected beginning immediately after birth and for 1 year.
The researchers followed up the children until 3 years of age and allergic symptoms were noted.
A skin prick test was used to ascertain atopy.
The team profiled bacterial communities in fecal samples by 16S ribosomal RNA-based polymerase chain reaction−temporal temperature gradient gel electrophoresis and next-generation sequencing.
BALB/c mice without and with ovalbumin sensitization/challenge were infected with candidate bacteria by oral gauge intragastric intubation.
Fecal, serum, lung, and colon tissue samples were collected from mice and analyzed for mechanisms of allergy development.
|Respiratory allergies were associated with an increased fecal abundance of Ruminococcus gnavus|
During the investigation period, 46% of children developed allergic diseases, including respiratory, and skin allergies.
The researchers deteced Lachnospiraceae at significantly higher frequency in allergic infants than nonallergic infants.
The high fecal count of Lachnospiraceae in allergic subjects appeared at 2 months of age and persisted until 12 months of age.
The enrichment of Lachnospiraceae in allergic infants was attributed to the overgrowth of Ruminococcus gnavus, which tended to have a low frequency in nonallergic subjects.
The team observed an increased Ruminococcus gnavus before the onset of allergic manifestations, and was associated with respiratory allergies or respiratory allergies coexistent with atopic eczema.
In mice, endogenous Ruminococcus gnavus grew rapidly after sensitization and challenge with ovalbumin.
Mice gavaged with purified Ruminococcus gnavus developed airway hyper-responsiveness and had histologic evidence of airway inflammation.
The team noted that expansion of Ruminococcus gnavus in mice stimulated secretion of cytokines by colon tissues, which activated type 2 innate lymphoid cells and dendritic cells to promote differentiation of T-helper 2 cells and production of their cytokines.
This led to infiltration of the colon and lung parenchyma by eosinophils and mast cells.
Dr Ni's team concludes, "In a study of a twin cohort, we associated development of allergies, particularly respiratory allergies, with increased fecal abundance of Ruminococcus gnavus."
"Mice fed Ruminococcus gnavus developed airway inflammation, characterized by expansion of T-helper 2 cells in the colon and lung, and infiltration of colon and lung parenchyma by eosinophils and mast cells."