HRH2 and Alzheimer disease: IL-18 acts on receptors (IL-18Rα) overexpressed on eosinophils in patients with AD and the histamine released by mast cells and basophils increases the expression of IL-18 on eosinophils by binding histamine with H2R and H4R, suggesting a relevant function of IL-18 and histamine in eosinophilic inflammation in AD.61