Mechanisms of immunotherapy.

Specific allergen injection immunotherapy is highly effective in IgE-mediated diseases, such as allergic rhinitis and venom anaphylaxis. Immunotherapy inhibits both early and late responses to allergen exposure. Immunotherapy is accompanied by increases in allergen-specific IgG, particularly the IgG4 isotype, which blocks not only IgE-dependent histamine release from basophils but also IgE-mediated antigen presentation to T cells. Immunotherapy acts on T cells to modify peripheral and mucosal T(H)2 responses to allergen in favor of T(H)1 responses. Recent studies have identified increased IL-10 production in peripheral blood and mucosal surfaces after immunotherapy. IL-10 has numerous potential antiallergic properties, including suppression of mast cell, eosinophil, and T-cell responses, as well as acting on B cells to favor heavy chain class switching to IgG4. These IL-10-producing cells might be so-called regulatory T cells and appear to be identified by the CD4(+)CD25(+) phenotype. Studies in mice suggest that dendritic cells play a vital role in induction of regulatory T cells. Novel approaches to immunotherapy currently being explored include the use of adjuvants, such as monophosphoryl lipid A or nucleotide immunostimulatory sequences derived from bacteria that potentiate T(H)1 responses. Alternative strategies include the use of allergen-derived peptides or modified recombinant allergen vaccines that act on T cells while minimizing the IgE-dependent mast cell activation that is dependent on the native allergen conformation.