Knockdown of claudin-1 expression level in the mouse models of AD (130) and AA (109) significantly exacerbated allergic inflammation, while the upregulation of claudin-1 expression level restored epithelial barrier function and decreased the severity of allergic diseases in these mouse models (131, 133), proving that downregulation of claudin-1 expression level contributes to the pathogenesis of allergic inflammation. The gene discussed is CLDN1; the disease is Alzheimer disease.