Cell-Mediated Food Allergies

Cell-mediated food allergies are sometimes called delayed hypersensitivity reactions. The symptoms of these reactions typically appear 6-24 hr after consumption of the offending food. Cell-mediated allergies involve the interaction of food allergens with sensitized lymphocytes. These reactions occur without the involvement of antibodies. The interaction between the allergen and the sensitized lymphocyte results in lymphokine production and release, lymphocyte proliferation, and the generation of cytotoxic T lymphocytes.

Lymphokines are soluble proteins that exert potent effects on tissues and cells, which results in localized inflammation. Lymphocyte proliferation increases the number of reactive cells, which magnifies the inflammatory process. The generation of cytotoxic or killer T cells results in cell destruction.

The T lymphocytes responsible for cell-mediated allergies are prevalent in the gut-associated lymphoid tissue. Gut lymphocytes are likely to be very critical in food-related, delayed hypersensitivity. However, the inaccessibility of these lymphocytes has made the evaluation of the role of cell-mediated reactions in food allergies quite difficult. As a result, the prevalence and importance of cell-mediated food allergies remain unknown.

Celiac disease, also known as gluten-sensitive enteropathy, is the one illness that seems likely to involve a cell-mediated mechanism. Celiac disease occurs in certain individuals following the ingestion of wheat, rye, barley, triticale, and sometimes oats. Although the mechanism of celiac disease is not completely understood, it appears to involve an immunocytotoxic reaction mediated by intestinal lymphocytes. On ingestion of proteins from the offending grains, the absorptive cells of the small intestinal epithelium are damaged.

The absorptive function of the small intestine is thus severely compromised, resulting in a malabsorption syndrome. The symptoms of celiac disease include diarrhea, bloating, weight loss, anemia from compromised iron absorption, bone pain from inadequate calcium absorption, chronic fatigue, weakness, muscle cramps, and, in children, failure to gain weight and growth retardation. Celiac disease is an inherited trait, but its inheritance is complex. The prevalence of this disease in the United States is about 1 in every 3000 individuals, although it occurs more frequently in Europe and Australia. Celiac disease rarely occurs in people of Chinese or African heritage. Its symptoms may begin at any age, and environmental factors, such as viral illness, may contribute to the onset of celiac disease in some cases. No evidence has been found of spontaneous recovery from the illness.

Celiac disease is triggered by the ingestion of the protein fractions, specifically the gluten proteins, of wheat and related grains. The gluten proteins are storage proteins in these grains that give them their characteristic baking functionality. Other grains, such as corn and rice, do not contain gluten proteins. As with IgE-mediated food allergies, most consumers do not react adversely to the ingestion of gluten. It is thought that the gluten proteins elicit a cell-mediated immune response in the intestinal lymphocytes.

A definitive diagnosis of celiac disease would necessitate a small bowel biopsy, in which the biopsy material is examined for evidence of flattened intestinal villi, which is characteristic of the disease. A normal appearance of subsequent biopsy material is restored after avoidance of wheat and related grains. Alternatively, a blood sample from the patient can be examined for the presence of antigluten antibodies. Many times, the diagnosis is made tentatively on the basis of symptomatic improvement after avoidance of wheat and related grains.

The treatment of celiac disease involves the total avoidance of wheat, rye, barley, triticale, and usually oats. Some, but not all, patients can tolerate oats. Ingredients that contain protein and are made from these grains must also be avoided, for small amounts of these foods can elicit adverse reactions. Unlike IgE- mediated allergies, the symptoms are usually delayed in onset by several hours to days. The normal absorptive function of the small intestine is restored within a few days with gluten avoidance.