IL21 and Alzheimer disease: Both AD patients and AD animal models present high CD4+/CD8+ T cell ratios indicative of Th1 skewing in the periphery (Browne et al., 2013), and elevated levels of IL-6, IL-21, IL-22, IL-23 in the serum of AD patients point to a Th17 polarization in the periphery during early disease (Oberstein et al., 2018).