Effects of Aging on Natural Killer Cell Activity and Activation by Interleukin-2 and IFN-α

To address the conflicting reports concerning both innate and lymphokine-inducible NK activity of elderly individuals, NK activity of peripheral blood mononuclear cells (PBMC) of 21 young (23 to 35 years old) and 43 elderly (65 to 100 years old) subjects was assessed using a 4-hr chromium release assay with K562 or Daudi cells as targets. Significantly higher innate NK cell activity was observed in elderly compared to young individuals (P < 0.001, Student t test). NK activity of both groups was enhanced to the same degree by IL-2. Although intermediate amounts of IFN-α (100 500 u/106 cells) induced comparable maximal NK activity of both young and elderly subjects, young subjects responded better than elderly to low amounts of IFN-α (10 u/106 cells), while higher amounts (103 u/106 cells) reduced the NK activity of the elderly, but not young, to basal levels. IFN-α also expanded the range of target cells susceptible to NK activity. Untreated cells of neither young nor elderly showed activity against Daudi targets. Two-hour treatment with IFN-α resulted in significant activity against Daudi cells; however, this activity was significantly lower in the elderly compared to the young subjects.