KLRB1 and HIV infectious disease: Loss of Vα7.2++CD161++ MAIT cells in HIV infection has previously been reported.13–16 One potential mechanism for this is through downregulation of CD161, resulting in a change in phenotype rather than loss of TCR+ cells.14 Indeed, in vitro MAIT cells downregulate CD161 upon activation.14,23 Given the disrupted intestinal epithelial integrity in HIV infection and the subsequent translocation of bacteria,13,24–26 activation of MAIT cells and subsequent downregulation of CD161 would be expected.