The harmful effect of CD4+ T lymphocytes in the pathogenesis of AD was also demonstrated via infiltration of T helper 17 (TH17) cells, a subtype of CD4+ T cells into the brain parenchyma, resulting in an increased level of IL-17 and IL-22 cytokines in the CSF, serum, and hippocampus of AD models. The gene discussed is IL17A; the disease is Alzheimer disease.