Immunological response to immunotherapy for immediate hypersensitivity: Clinical relevance

Immunotherapy, also called desensitization, is effective in treating allergic rhinitis, insect sting venom hypersensitivity and probably allergic asthma. Administration of gradually increasing doses of the sensitizing antigen induces several immunological changes. The humoral responses include an increase in specific IgG titer, a decrease in specific IgE titer with blunting of its seasonal rise, and an increase in the specific anti-idiotype antibody titer. Cellular changes include diminished responsiveness of the patient's lymphocytes to stimulation by allergen as measured by thymidine incorporation. This is accounted for by the generation of suppressor cells specific for the allergen. These suppressor cells also induce suppression of IgE production by mononuclear cells. An additional effect that is attributed to IT is a decrease in basophil sensitivity to the allergen as measured by histamine release. The clinical correlates of these changes are not clear. Currently, none of the responses can be used as a tool for assessing the response in the treated individual patient. Although the increase in specific IgG was shown to correlate with the clinical response in patient groups, it is not applicable to the individual patient. Currently the best parameter for assessing clinical response is probably the increase in the ratio between the specific IgG and the specific IgE. However further studies are warranted to evaluate the significance of the change in anti-idiotype antibodies, basophil histamine release and perhaps immunological changes yet to be discovered.