Antigen absorption: food, fire or fuel?

The epithelium of the gastrointestinal tract is constantly exposed to varieties of antigens. In healthy individuals, only small amounts of ingested dietary antigens are absorbed. The normal immune response to absorbed food antigens is one of tolerance, which enables food to play its nutritive ("food") role without causing disease. Breakdown in tolerance may result in a spectrum of clinical problems, including food allergy, food sensitive enteropathy and food intolerance ("fire"). When food-sensitive enteropathy is subclinical, continued ingestion of the offending food antigen sometimes results in development of tolerance and resolution of the enteropathy. The development of tolerance to a specific food antigen under these circumstances may be prevented by briefly excluding the antigen from the diet, substituting it with a different antigen and then reintroducing the first antigen. In this situation, the second food antigen not only prevents the mucosal recovery expected if the infant had been continuously fed food containing the first antigen alone, but frequently seems to worsen the damage when the first antigen is reintroduced ("fuel"). While genetic constitution seems to be the major player in the heightened IgE responsiveness in atopic subjects, the pathophysiology of food-sensitive enteropathy in non-atopic children is less well understood. Complex interplay between environmental factors such as breast feeding, and host factors such as the integrity of the absorptive gut epithelium and its immunological responsiveness at the time of introduction of various food antigens seems to be important in its genesis as well as in its tendency to be a transient disorder of infancy.