Allergen immunotherapy (AIT) is the administration of the causal allergen to control allergic inflammation and symptoms. AIT has been used for over a century and it is really reflected the only disease-modifying therapy for IgE-mediated allergic diseases, because it induces a persistent immunological and clinical tolerance toward the causal allergen. Both subcutaneous AIT (SCIT) and sublingual (SLIT) are used and accepted as effective treatments for adults and children with allergic rhinitis (AR) with or without asthma. Existing studies recommend that both SLIT and SCIT can induce the same immunologic changes.AIT can modify the upper and lower respiratory allergic symptoms by modulating the IgE-mediated response following the allergen exposure. An important mechanism in achieving immunologic tolerance is the upregulation of allergen-specific Tregulatory (Treg) cells and B-regulatory (Breg) cells, which primarily down-regulate the Th2 response Over the last 20 years, sublingual allergen immunotherapy has expanded popularity based on controlled trails that have revealed a favourable safety profile.

Immunotherapy, Bronchial Asthma