ABSTRACT
Allergen immunotherapy for inhalant allergens is effective when products of proven value are used in carefully selected patients with symptoms on exposure to the relevant allergen(s) and objective confirmation of IgE sensitivity. The traditional subcutaneous route is highly effective and safe when administered in a specialist clinic by trained and experienced staff. The sublingual route has emerged as an effective and safe alternative for specialist prescription that may be safely self-administered in the patients’ home. Allergen immunotherapy in contrast to anti-allergic drugs, including modern anti–type 2 biologics, is disease modifying and may result in durable disease remission. The mechanism of this long-term tolerance has been shown to involve suppression of allergen-specific Th2 type T-lymphocyte responses. This occurs as a consequence of preferential early induction of regulatory T cells and B cells, followed by immune deviation in favor of allergen-specific type 1 responses. As a consequence, there is a reduction in tissue eosinophilia and increases in allergen-specific IgG and IgA antibodies. These “blocking” antibodies compete with IgE for the binding of allergen with consequent reduction in IgE-dependent activation of mast cells and a decrease in IgE-facilitated allergen presentation. Broadly similar mechanisms have been shown to be involved for oral immunotherapy for food allergy that has been shown to reduce the risk of allergic reactions following accidental exposure to the relevant food, whereas in contrast to inhalant allergen immunotherapy, there is no evidence that oral immunotherapy may induce durable tolerance after discontinuation of the treatment.
