Mechanisms of specific immunotherapy: current knowledge.

Induction of specific unresponsiveness (tolerance) in peripheral T cells by IL-10 and/or TGF-beta and recovery by cytokines from the tissue microenvironment represent two key steps in specific immunotherapy of allergy and natural exposure to allergens in healthy individuals. IL-10 and TGF-beta elicit tolerance in T cells and thereby control the suppression and development of antigen-specific immunity. Both cytokines also play an important role on the generation of a non-inflammatory IgG4 and IgA type of allergen--specific antibodies during the course of specific immunotherapy. Histamine plays an important role in upper and lower airway inflammation. In addition to its well-characterized effects in the acute inflammatory and allergic responses, histamine regulates several aspects of antigen-specific immune response development. Histamine affects the maturation of dendritic cells and alters their T cell polarizing capacity. Histamine regulates antigen specific Th1 and Th2 cells as well as related antibody isotype responses. Histamine and four different known histamine receptors (HR) display a very complex system and their expression changes according to the stage of cell differentiation as well as microenvironmental influences.