PDCD1 and Cognitive impairment: Saresellaa et al. [24] found that PD-1neg Treg cells might play an important role in the pathogenesis of Alzheimer's disease; loss of such cells and their functional ability is associated with development of Alzheimer's disease by studying the expression of PD-1 in different subgroups of Treg cells in patients with cognitive impairment and Alzheimer's disease.