Implications of nasopharynx-associated lymphoid tissue (NALT) in the development of allergic responses in an allergic rhinitis mouse model

Background Nasopharynx‐associated lymphoid tissue (NALT) serves as an important inductive site for mucosal immunity in the upper respiratory tract. Despite its importance in the mucosal immune system, little is known regarding the role of NALT in airway allergic immune responses. We aimed to elucidate the role of NALT in the induction of upper airway allergic responses in a mouse model. Methods Inhibitor of DNA binding/differentiation 2 (Id2)−/− and Id2+/− mice was exposed to the ovalbumin (OVA)‐induced allergic rhinitis model, because the former resulted in the NALT deficiency. The allergic parameters, such as allergic symptoms, serum OVA‐specific immunoglobulin E (IgE) levels, eosinophil infiltration, and cytokine profiles in the nasal mucosa, were compared between Id2−/− and Id2+/− groups. Results NALT‐null, Id2−/− mice displayed significantly lower allergic responses compared with Id2+/− mice, as demonstrated by lower levels of allergic symptoms, serum OVA‐specific IgE, eosinophilic infiltration, and local Th2 cytokine transcriptions. To determine which of two factors, that is, the absence of NALT or the alteration of immunocompetent cell populations caused by the Id2 deficiency, has a larger effect on the attenuated allergic immune responses in Id2−/− mice, lethally irradiated Id2−/− mice were engrafted with C57BL/6 wild‐type bone marrow cells and showed still significantly lower allergic immune responses compared with equally treated Id2+/− mice. In addition, IgE class switch recombination‐associated molecules, such as ε immunoglobulin heavy‐chain germline gene transcript, ε mRNA, and activation‐induced cytidine deaminase mRNA, were detected in NALT from OVA‐sensitized wild‐type mice. Conclusion These results show the critical role of NALT for the induction of allergic responses in the upper airway at least in part by means of class switching to IgE in situ.