NELFCD and airway hyperresponsiveness: By affecting the differentiation of Th1/Th2 cells, the release of Th1 cytokines decreases and Th2 cytokines increases, resulting in chronic airway inflammation [18,19].The decrease in the Th1/Th2 cell ratio is the initiation and maintenance factor of airway inflammation and airway hyperresponsiveness, and Th2 dominance is the central mechanism for the formation and progression of CVA [20].