[T gamma-delta lymphocytes and their role in hypersensitivity processes in the digestive and respiratory mucosa]

Specific antigenic recognition by the immune system relies on receptors that T and B lymphocytes display on their plasmatic membranes. Most T cells express an antigen receptor integrated by an a chain and a b chain, the TcR-alphabeta. There is also a second population of T cells, minority in blood, spleen and lymph nodes, which expresses a different type of TcR, the TcR-gammadelta. These cells, termed gammadelta T cells, are probably implicated in the innate immunity, and are preferentially located in epithelia, where they are known as "gammadelta intraepithelial lymphocytes" (gammadelta IEL). The intestinal gammadelta IEL population (gammadelta i-IEL) is particularly abundant and it might have, at least in part, an extrathymic origin. An increase in the gammadelta i-IEL population has been described in intestinal hypersensitivity processes like Alimentary Allergy and, characteristically, Celiac Disease, but its significance is not well known. The second best known gammadelta IEL subset is the one located in the respiratory mucosa. Recent data suggest that these gammadelta IEL might play a role in protecting the normal airway function while being also implicated in allergic airway diseases, like Allergic Rhinitis and Asthma, due to their pro-inflammatory functions. This review focuses on the general characteristics of this yet poorly known and intriguing T cell population, whose relevance is increasingly acknowledged.