Objective To investigate the expressions of IL-18,IL-18 binding protein isoform a(IL-18BPa)and IL-18Rα in blood CD4+Th1 cells of patients with allergic asthma(AA),and with allergic rhinitis and asthma syndrome(ARA),and the effects of allergens on their expressions.Methods Blood samples were collected from patients with AA,ARA and healthy control(HC)subjects.Flow cytometry was used to evaluate the actions of allergens on the expressions of IL-18,IL-18BPa and IL-18Rα in CD4+Th1 cells.Ovalbumin(OVA)-induced AA mouse models were established,and the expression level of IL-18Rα along with the influence of IL-18 on its expression in blood and lung Th1 cells was also explored by flow cytometry.Results Compared with HC,we observed increased IL-18 while decreased IL-18BPa expression in blood Th1 cells of AA and ARA patients.Moreover,allergens upregulated the expression levels of IL-18,IL-18BPa and IL-18Rα in Th1 cells of patients with AA and ARA.Additionally,intratracheal challenge with OVA plus IL-18 increased the proportions of blood and lung Th1 cells of HC and AA mice,and upregulated IL-18Rα expression on blood and lung Th1 cells of HC mice.Conclusion Allergens may be involved in the pathogenesis of airway allergic diseases by inducing the expressions of IL-18 and IL-18Rα in CD4+Th1 cells.