T lymphocytes and food allergy

Food allergy is a hypersensitivity reaction to normally harmless substances and involves humoral immune responses, mediated by immunoglobulin (IgE) synthesized by B lymphocytes, and cellular immune responses mediated by T lymphocytes. An IgE-mediated mechanism leads to clinical symptoms occurring immediately after food ingestion, e.g., the oral allergy syndrome. For delayed reactions involving the gastrointestinal tract or the skin, the underlying immune mechanisms are less clear. In order to elucidate the cellular response to food allergens, human allergen-specific T cell cultures generated in vitro represent helpful tools. The majority of food allergen-specific CD4(+) T lymphocytes isolated from food-allergic individuals was found to synthesize high levels of IL-4 and IL-13, two cytokines required for initiation of IgE synthesis. Due to selective homing profiles, food-specific T cells seem also to be involved in defining the target organ of the allergic inflammation. Recent data provide evidence that in addition to IgE-mediated inflammation, food allergen-specific T lymphocytes may also cause inflammatory responses independently of IgE-mediated mechanisms.