Circulating T follicular helper (TFH) and T follicular regulatory (TFR) cells are subsets of CD4+ T cells with modulatory properties. TFH cells play a role in maintaining formation and differentiation of B cell follicles within the germinal centre and are also responsible for plasma cell differentiation and class switch recombination. Regulatory T cells have been shown to play a crucial role in regulating germinal centre response. TFR cells shares similar properties with TFH cells with regulatory properties and are thought to play a role in the immune tolerance induction following allergen-specific immunotherapy. This involves the administration of high dose allergen either subcutaneously or sublingually and has been shown to confer benefit to patients by inducing long-term clinical and immunological tolerance. The overall aim of this study is to evaluate the role of circulating interleukin (IL)-21 producing TFH cells in the pathophysiology of grass pollen-induced allergic rhinitis. Furthermore, we will assess the effect of grass pollen subcutaneous and sublingual immunotherapy on IL-21+ TFH cells in peripheral blood.
Seasonal allergic rhinitis is an inflammatory disease of the mucosal lining and is caused by allergens from tree, grass or pollen and it affects 20% of the population in Western Europe. Most patients with seasonal allergic rhinitis responds to medications, however a small proportion of patients do not. Allergen-specific immunotherapy has been shown benefit these patients by inducing long-term tolerance for several years upon termination of treatment, but the mechanism is still unclear. T helper cells play an important part in the pathophysiology of allergy. We aim to investigate T cell subsets namely T follicular helper (TFH), T follicular regulatory (TFR) cells, and TFH cells that produce a protein called interleukin (IL)-21 that are thought to play a part in the tolerance induction in allergic individuals following immunotherapy.