IL9 and Alzheimer disease: Although the mechanism underlying the decrease in IgE levels in patients with AD remains unclear, polymorphisms in several cytokine genes, such as interleukin (IL)-3, IL-4, IL-5, IL-9, IL-13, and granulocyte-macrophage colony-stimulating factor (GM-CSF), regulate total serum IgE levels and are associated with atopy-related traits [31].