Molecular and Cellular Mechanisms of Food Allergy and Food Tolerance

One may not believe it, but there is an entire universe in one's belly.  One's guts, in and of themselves, are over 300 square meters in surface area, and are home to thousands of different species of bacteria, as well as an immune system that is exquisitely tailored towards sensing, which of the 300 kilograms of food ingredients  that we ingest each year are safe, and which are unsafe.  So in this veritable universe of bowel, it is incredibly difficult to figure out what decides whether one becomes allergic or tolerant to food.

Chintharajah et al tackle this problem in this month’s issue of JACI (J Allergy Clin Immunol 2016; 137(4): 984-997).  They begin by surveying the types of immune cells that service our gut.  They highlight the central role of a specific type of immune cell called the dendritic cell, which lives in the walls of the small intestine (among other areas), in capturing the proteins in food particles, processing them, and then presenting them to other types of immune cells.  In certain circumstances, particular food proteins, chemical messengers from the gut, and the genetic makeup of immune cells can move the immune system into a pro-allergic state.  Perhaps just as important is the role of another type of immune cell, the regulatory T-cell, which ensures the proper balance of immune responses.  When these regulatory T-cells don’t work properly, the immune system can go into overdrive and become less likely to see food proteins as safe and tolerable.

Interestingly, a lot of other surprising factors that may lead to food allergies.  The microbiome is not limited to the gut. The skin has its own microbial ecology and skin breakdown and inflammation can alter the skin microbiome and allow sensitization to aerosolized food antigens such as peanut dust.  in addition,  the gut bacteria in children with food allergies are less diverse and have different levels of different types of bacteria compared to children without food allergies. 

All of these factors need to be taken into consideration when one tries to   modify the immune system to nudge it away from producing an allergic response.  There are ongoing studies trying to figure out how to desensitize allergic individuals to certain foods.  Knowing how these approaches alter the immune system will help take those techniques out of research centers and into the allergist’s office.