Regarding PD-1, the expression level of PD-1 and the percentage of the PD-1+ population in the AD patients’ T-cell subsets (CD3+, CD3+CD56+, CD4+, CD8+, and CD8+CD25+ T cells) were similar to those in the healthy volunteers, and only a higher PD-1 expression trend was found in CD4+CD25+ T cells (Fig. 2A, Additional file 1: Figure 2). This evidence concerns the gene NCAM1 and Alzheimer disease.