The exact mechanism of action of allergen extract during allergen immunotherapy (AIT) course is not fully understood till now.

AIT leads to a change in the immune response of T-lymphocytes, followed by an increase in the level of specific antibodies (IgG4 and/or IgG1 and, and in some cases, IgA) and a decrease in the level of specific IgE. A secondary immune response is an immune deviation of specific T cells from Th2 towards Th1.