Routinely, human natural killer (NK) lymphocytes are identified as CD3eneg CD56bright or dim. CD3neg CD56neg cells with low perforin are found in viremic patients infected with human immunodeficiency virus and hepatitis C virus (reviewed, N.K. Bjorkstorm et al., Trends Immunol. 31:401, 2010). To our surprise, we found by flow cytometry that CD3neg perforin(PRF1) positive NK cells included as many as 50% CD56neg cells within the blood of 97 healthy subjects. Among these subjects (aged 21 to 62 years), the CD3eneg PRF1positive cells included at least 10% CD56neg cells in 24 of 97 (~25%) subjects. CD56neg perforin high CD3neg cells were over 50 cells/mm3 of blood in 14% of the healthy donors. As anticipated, the CD56dim cells had ~7 fold higher perforin MFI than the CD56bright cells. Notably in the healthy donors with high frequencies of CD56neg cells, these cells had bimodal perforin levels comparable to the levels in the CD56bright and CD56dim subsets. The perforin levels indicate that many CD56neg NK cells may have strong cytotoxicity in healthy donors in contrast to the low perforin and cytotoxicity observed in CD56neg NK cells of the viremic patients. We conclude that CD56neg NK cells now warrant attention as potential cytotoxic cells after receiving considerable attention as high chemokine-secreting cells.
- Copyright © 2011 by The American Association of Immunologists, Inc.