A study of the mechanisms of switching the immune response to the IgG4 synthesis during allergic diseases with specific immunotherapy showed that in the repeated administration of the allergen, a change in the immune response to the antigen occurred with an increase in the concentration of the immunosuppressive cytokine IL-10, and in the level of Treg cells (CD25+Foxp3+CD4+), mediating mechanisms of tolerance to a specific antigen. The gene discussed is IL10; the disease is allergic disease.