Cell-mediated food allergies are sometimes called delayed hypersensitivity reactions, because the symptoms of these reactions typically appear 6 to 24 hours after consumption of the offending food. Cell-mediated allergies involve the interaction of food allergens with sensitized lymphocytes, usually in the intestinal tract. These reactions occur without the involvement of IgE or other 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 profound effects on tissues and cells resulting in localized inflammation. Lymphocyte proliferation increases the number of reactive cells thus magnifying the inflammatory process. The generation of cytotoxic or killer T cells results in the destruction of other intestinal cells including the critical absorptive epithelial cells.
The T lymphocytes responsible for cell-mediated allergies abound in the gut-associated lymphoid tissue. Intestinal T lymphocytes are likely to be very critical in food-related, delayed hypersensitivity. However, the inaccessibility of these lymphocytes has hampered experimental studies of the role of cell-mediated reactions in food allergies. As a result, the prevalence and importance of cell-mediated food allergies remains unknown.
Celiac disease, also known as gluten-sensitive enteropathy, is the one illness that seems likely to involve a cellmediated mechanism. Celiac disease occurs in certain individuals following the ingestion of wheat, rye, barley, triticale, and perhaps oats. Although the mechanism of celiac disease is not completely understood, an immunocy-totoxic reaction mediated by intestinal lymphocytes is probable. On ingestion of proteins from the offending grains, the absorptive cells of the small intestinal epithelium are damaged and the absorptive function of the small intestine is severely compromised, resulting in a malabsorption syndrome. The symptoms of celiac disease include diarrhea, bloating, weight loss, anemia from inadequate iron absorption, bone pain from impaired calcium absorption, chronic fatigue, weakness, muscle cramps, and, in children, failure to gain weight and growth retardation. The prevalence of celiac disease in the U.S. is not precisely known but is thought to be about 1 in every 2000 individuals. Celiac disease appears to occur more frequently in Europe and Australia. Celiac disease rarely occurs in individuals of Chinese or African heritage. Celiac disease may manifest at any age. Environmental factors, such as viral illness, may possibly contribute to the onset of celiac disease in some cases.
Celiac disease is triggered by the ingestion of the protein fractions, specifically the gliadin proteins, of wheat and related grains. Other grains, such as corn and rice, do not contain similar gliadin proteins. As with IgE-mediated food allergies, most consumers do not react adversely to the ingestion of these particular grain proteins. In susceptible individuals, a particular segment of the gliadin protein interacts with the sensitized T lymphocytes to elicit a cell-mediated immune response.
The most definitive diagnosis of celiac disease requires taking a small bowel biopsy. The biopsy material is examined for evidence of flattened intestinal villi, a feature that is characteristic of the disease. A normal appearance of the 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 antiendomy-sial antibodies, which are elevated in celiac patients. Because of the invasiveness of the biopsy procedure, the diagnosis is often made tentatively on the basis of symptomatic improvement after avoidance of wheat and related grains.
Celiac disease is also treated with thorough implementation of an avoidance diet. In the case of celiac disease, the total avoidance of wheat, rye, barley, triticale, and perhaps oats is usually advocated. Some, but not all, patients can tolerate oats. Ingredients derived from wheat, rye, barley, and oats that contain protein must also be avoided. The tolerance of celiac sufferers for these grains is not precisely known, but it is thought that small amounts of these foods can provoke reactions.
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