IL17A and Alzheimer disease: Although further research is needed on the role and regulatory mechanism of Th17 cells in AD occurrence and development, current research practices reveal that their functions are related to released cytokines, such as Th17 cell infiltration in AD patients’ brains induced by β-42 injection, and in an AD rat model, levels of IL-17 and IL-22 were found to be higher in the brain parenchyma, cerebrospinal fluid, and serum (Zhang et al., 2013).