Food antigen handling by the gut
1981
Levinsky, R.J.
Although the intestinal mucosa serves as a barrier between gut contents and body tissues, the barrier is incomplete. Food protein antigens may be absorbed intact into the circulation; antibodies to food proteins have been demonstrated in healthy persons. Most individuals do not exhibit hypersensitivity reactions to foods. Neonates acquire passive immunity to antigens from the mother via breast milk, because the newborn gut is initially freely permeable to macromolecules such as immunoglobulins. Later, breast milk stimulates gut closure, reducing enteric antigen entry. Despite immunoglobulin antibodies lining the mucosal surface, some macromolecular proteins are absorbed. These proteins help to maintain mucosal immunity at sites other than the gastrointestinal tract, and orally induce tolerance to foods. Immune complexes containing food antigens usually do not provoke allergic symptoms. The composition of these complexes appears to be different, however, in healthy and atopic subjects, with IgA deficiency being associated with food allergies. Breakdowns in food tolerance cause excessive entry of food macromolecules and the formation of harmful immune complexes which may lead to many diseases. (nm)
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