Different methods of local allergen-specific immunotherapy.

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In the treatment of allergic disorders, specific immunotherapy (SIT) occupies a central role as the only currently available causal method of treatment. The concept of ‘‘local immunotherapy’’ includes all nonsubcutaneous forms of SIT, which are used to treat allergic disorders such as rhinitis and asthma. Nasal, bronchial, oral and sublingual administration of allergen extracts is regarded as local immunotherapy (LIT). Attempts were made very early to produce tolerance to certain allergens by the oral route. Dakin reported in1829 that North American Indians regularly chewed small amounts of leaves of the ‘‘poison ivy’’ (Rhus toxicodendron) in order to prevent or weaken the severe dermatitides that occur after contact with this plant (Dakin, 1829 quoted after (1)). In 1900, 11 years before the first work on subcutaneous immunotherapy, Curtis published an article about the efficacy of oral allergen-specific immunotherapy (OIT) in hay fever (2). This was followed five years later by other reports about the success of OIT in cow’s milk allergy (3). In the 1920s and 1930s, too, reports of positive experiences with this method appeared again and again. However, a negative, multicentre comparative study of ragweed pollinosis (4) (in which, interestingly, good results were reported in children!) severely limited the use of OIT in adults in the Anglo-Saxon countries. In the early 1950s, Schuppli in Basel, Switzerland took up OIT again. His positive results in children ensured that this method soon became widespread (5–12). New methods of local application were sought, because various studies in recent years showed that OIT is clearly inferior to allergen-specific subcutaneous (injected) immunotherapy (SIT) with regard to both clinical and immunological efficacy. From a clinical aspect however, there is a whole series of arguments to explain the preference for LIT compared to injected IT. Poor compliance can limit the applicability of injected SIT (13). Because LIT can be carried out at home by the patient and the injections in the doctor’s office are no longer necessary, greater compliance is ascribed to LIT than to SIT. However, more precise studies of this subject are lacking, so the effective compliance of LIT patients is not known. Severe systemic side-effects restrict the broad use of SIT, although the risk in hay fever patients is lower compared to asthma patients (14, 15). When SIT is carried out correctly, severe systemic side-effects in patients with allergic rhinitis, who are treated with potent extracts, occur in about 5% of all the SIT injections (16). Based on the published data, on the other hand, systemic side-effects appear to occur only very rarely with LIT. The rapid development of molecular biology and progress not only in general allergen characterization but also in the production of large quantities of recombinant allergens have reawakened interest in recent years in local immunotherapy (LIT), both in science and among the producers of allergen extracts. At present there appears to be a trend away from oral towards sublingual allergen-specific IT (SLIT).