ABSTRACT
I. INTRODUCTION "Immunologic tolerance" describes the inhibition or absence of an immune response and, when used in the therapeutic sense, inhibition or elimination of only pathogenic immune responses, leaving the beneficial functions, such as protective immunity, intact (1). Although tolerance is often used to refer to responses to self-antigens, tolerant T-and B-cell responses can occur to both self and non-self antigens. In contrast to immunosuppressive and/or anti-inflammatory drugs, tolerizing agents induce an altered immune response that persists after the agent has been stopped. Tolerance in this chapter denotes a clinical state in which the allergen, after the discontinuation of allergen immunotherapy, no longer induces allergic symptoms. Studies to demonstrate that allergen immunotherapy
induces long-term changes in the natural history of allergy have only recently become convincing because they included critical controls. The most detailed studies of immunotherapy have focused on I year or less of allergen injections, and such short duration of therapy does not generally induce tolerance. Several studies have demonstrated that, following prolonged insect venom immunotherapy, patients are protected from systemic reactions to stings for at least several years after therapy is stopped. In addition, a carefully controlled study of immunotherapy with grass pollen allergen provides strong evidence that allergen immunotherapy induces a clinical effect which persists at least 3 years after therapy is stopped (2).
