CD4 and Alzheimer disease: Specifically, CD39+ resting CD4+ Treg % CD4+ Treg, HVEM on TD CD4+ T cell, and CD4RA on TD CD4+ T cell may act as harmful factors in AD, whereas CD45RA-CD4+ T-cell AC, CD45RA-CD4+ T cell % CD4+ T cell, EM CD4+ T-cell AC, CD25 on switched memory B cell, and CD4 on CD45RA+ CD4+ T cell may serve as protective factors.