Potential confusion of contaminating CD16+ myeloid DCs with anergic CD16+ NK cells in chimpanzees.

Precise identification of NK-cell populations in humans and nonhuman primates has been confounded by imprecise phenotypic definitions. A common definition used in nonhuman primates, including chimpanzees, is CD3(-) CD8α(+) CD16(+) , and this is the dominant NK-cell phenotype in peripheral blood. However, recent data suggest that in chimpanzees a rare CD8α(-) CD16(+) population also exists. Herein, we present evidence validating the existence of this rare subset in chimpanzee peripheral blood, but also demonstrating that gating on CD3(-) CD8α(-) CD16(+) cells can inadvertently include a large number of CD16(+) myeloid DCs (mDCs). We confirmed the inclusion of mDCs in CD3(-) CD8α(-) CD16(+) gated cells by demonstrating high expression of CD11c, BDCA-1 and HLA-DR, and by the lack of expression of NKp46 and intracellular perforin. We also functionally validated the CD8α(-) NK-cell and mDC populations by mutually exclusive responsiveness to a classical NK-cell stimulus, MHC class I-deficient cells, and a prototypic mDC stimulus, poly I:C, respectively. Overall, these data demonstrate common problems with gating of NK cells that can lead to erroneous conclusions and highlight a critical need for consensus protocols for NK-cell phenotyping.