TIGIT and HIV-1 infection: Compared with healthy donors, proportionally increased TIGIT expression on NK cell subpopulations, including NKG2A+NK cells, NKG2C+NK cells, NKG2A+NKG2C−NK cells and NKG2A−NKG2C+NK cells was only observed in chronic HIV-1 infection over 2 years (Figures 4E,F, all P < 0.05).