Researchers from Boston Children’s Hospital have discovered skin-gut communication which explains a link between food allergy and atopic dermatitis. The research shows that the immune response triggered on scratching the skin can lead to an increased number of activated mast cells in the small intestine resulting in an allergic reaction.
Atopic dermatitis is a type of eczema characterised by dry, itchy skin. It is a strong risk factor for developing food allergy, but the exact relationship between the two conditions remained unclear. As itching is a major symptom of atopic dermatitis, people with the disease, especially babies, often scratch their skin. The current study reveals that scratching the skin initiates mast-cell expansion in the intestine.
The study was conducted on mice. Scratching was induced by tape stripping mouse skin (by applying and removing small strips of tape on the skin of mice). Researchers found that on scratching some cells produced a cell-signalling protein called IL-33, which entered the bloodstream. On reaching the gut IL-33 works in concert with IL-25, a protein secreted by cells in the lining of the intestine, to activate type 2 innate lymphoid cells (ILC2s). Activated ILC2s made two additional cell-signalling proteins, IL-13 and IL-4, which were found to be responsible for the expansion of intestinal mast cells.
Expansion of intestinal mast cells made the intestinal lining more permeable making it easier for allergens to enter the tissues. The researchers revealed that the mice that underwent tape stripping had more severe reactions to food allergen than mice that did not.
Finally, the intestinal biopsies from four children with atopic dermatitis also showed to contain more mast cells than those from four children without the condition, reported the National Institute of Allergy and Infectious Diseases (NIAID) who supported the study.
Although additional work is needed to determine the relevance of the findings to humans, the researchers suggest that interventions to reduce itching could potentially lessen the severity of food allergy among people with atopic dermatitis.