CD4 and type 2 diabetes mellitus: Percentages of PD-1+ CD4+ T cells and PD-1+ CD8+ T cells were significantly increased in the T2DM, SS, and SS+T2DM groups than in the healthy control group, and were the highest in the SS+T2DM and SS groups, but no significant difference was detected between the SS+T2DM group and SS group (Fig 1, Table 1).