A stage-dependent analysis revealed a negative correlation between CD28 + CD4 + T cells and total tau (p = 0.0005; Table 2b), between CTLA-4 + CD4 + T cells and Amyloid-β 1–40 (p = 0.0362) and Amyloid-β 1–42 (p = 0.0243; Table 2c) and between ICOS + CD4 + T cells and Amyloid-β 1–40 (p = 0.0194) and Amyloid-β 1–42 (p = 0.0323) in mild AD. Here, CD28 is linked to Alzheimer disease.