Allergy as an organ and a systemic disease.

Allergic disorders are viewed generally as organ diseases and thus referred to organ specialists, such as the ear, nose and throat specialist for rhinitis, the pulmonologist for asthma, the dermatologist for dermatitis, and so on. Indeed, the systemic nature of allergy is made evident by the fact that the same individual may develop during the life different manifestations to a given allergen. This is true for example in sensitisation to house dust mites, which may start in childhood as atopic dermatitis and later express as asthma or rhinitis. The major player in driving the immune response is the T lymphocyte, and the T helper subpopulations--Th1 and Th2--as well as the T regulatory cells, are involved in orienting tolerance or reactivity to allergens. Interesting observations on the systemic or organ-specific actions of T cells were obtained by transplantations from allergic donors to non-allergic recipients. Bone marrow is able to transfer all allergic manifestations, while lung transplantation transfers only asthma. A number of factors are involved in the expression of allergy as a systemic or organ disease and deserve deeper investigations. They include the antigen presenting cells, the homing of T cells, the cytokine and chemokine pattern, and the adhesion molecules.