IL17A and Alzheimer disease: Compared with control group, patients with AD had an increased proportion of Th22 cells [weighted mean difference (WMD) = 2.07, 95% CI (1.33, 2.81), <i>p</i> < 0.001], Th17 cells [WMD = 1.04, 95% CI [0.66, 1.43], <i>p</i> < 0.001], IL-17 [WMD = 17.56, 95% CI (11.1, 24.03), <i>p</i> < 0.001], and a decreased proportion of Tregs [WMD = -2.49, 95% CI (-2.93, -2.05), <i>p</i> < 0.001] in peripheral blood.