The identification of new T-cell subsets, such as follicular helper T (Tfh) cells, has increased our understanding of the complex immunological networks involved in allergic disorders. This paper reviews the evidence supporting Tfh cells in regulating immunological responses to allergens, with a particular emphasis on IgE production, and addresses the implications of such regulation in allergen-specific immunotherapy. In animal models of allergic disorders, Tfh cells aid in the synthesis of IgE. The type 2 fraction (Tfh2) of Tfh cells is thought to be the main actor in secreting IL-4 and promoting isotype flipping to IgE. Notably, the frequency of Dermatophagoides pteronyssinus group 1 (Der p 1)-specific IL-4+ Tfh cells in blood was shown to be positively associated with serum Der p-specific IgE levels in individuals with allergic rhinitis. Der p 1-specific IL-4+ Tfh cells decreased after allergen immunotherapy (AIT) in allergic rhinitis patients, which was linked with clinical symptom remission.
Allergen-specific IL-4+ Tfh cells contribute to allergen-specific IgE production and correlate with clinical effectiveness of AIT in allergic rhinitis patients, implying that allergen-specific Tfh cells are a viable therapeutic target and biomarker for AIT in allergic rhinitis.