Study of Cellular Antigen Stimulation Test (CAST) in the Diagnosis of Cellular Allergy to Food Additives

Abstract

Food allergy is an adverse health effect due to a specific immune response occurring on exposure to a particular food substance. This immune response is; in the most part; the consequence of either loss of or failure to induce oral tolerance. Food allergy is a major health problem affecting 1-10% of the population with a significant impact on the quality of life. Food allergies are usually categorized into IgE-mediated and non IgE-mediated (cell-mediated) types. The latter type remains the entity of food allergy with less understanding and under-estimation. This owes to delayed onset of symptoms and inconvenient accessible diagnostic tools. Accurate and meticulous diagnosis of food allergy is mandatory. After detailed history, specific diagnosis relies on skin tests and allergen specific IgE. However; being the gold standard for diagnosis of food allergy; oral food challenge test remains the reference against which all approaches are verified. Food additives by all its categories especially preservatives, are an entity that contribute to a significant number of cases of food allergies according to data of medical history. Many theories were postulated for the underlying pathophysiology of sensitivity to food additives. The most accepted one is pseudoallergy through Cox enzyme inhibition with the subsequent release of leukotrienes. Therefore, approaches for identification of the culprit food additive in hypersensitive patients should be sufficiently conclusive. Depending on the traditional diagnostic tools; including oral food challenge test; is unsatisfactory due to difficulties such as varying doses of individual additives and difficulty in standardization of the outcome. As a result of the fore-mentioned details, novel cellular tests were developed with principles dependant on determination of the reactivity of blood cells in vitro, particularly basophils. An important illustration is the cellular antigen stimulation test (CAST-ELISA). It is based on the quantification of the sulphidoleukotrienes (LTC4, D4, E4) released from allergen-activated IL-3 primed basophils in vitro. The main application of CAST is in evaluation of non IgE-mediated reactions. Moreover, it is somewhat reliable in assessment of food allergy and drug allergies. CAST can also be helpful in evaluation of sensitivity to food additives and preservatives, owing to the fore-mentioned principle pathophysiologic mechanism accused of being involved in this category of sensitivities. However, its implementation as a first line test in diagnostic workup of allergy is deferred due to the elevated cost and low sensitivity compared to specific IgE.