IL17A and Alzheimer disease: Th1 cytokines TNF-α (P < 0.001) and IFN-γ (P < 0.01) peaked on day 14 but decreased on day 21 after AD, whereas Th2 cytokines (IL-4 and IL-6) and Th17 (IL-17A) persistently up-regulated and peaked on day 21 (P < 0.001).