Natural killer cell function is not diminished in the healthy aged and is proportional to the number of NK cells in the peripheral blood.

We studied natural killer (NK) cell subsets and NK function in young (25-35 years) and aged (75-84 years) persons by means of the single-cell assay. The subjects admitted to the study all fulfilled the SENIEUR health criteria in order to avoid confounding factors such as underlying disease or the influence of medication. We found no significant difference in the NK function between healthy young and aged persons on a per cell basis. A new application of the two-wavelength immunofluorescence technique during the single cell assay made it possible to define the phenotypes of the conjugate-forming cells responsible for the natural killer function. Most of the conjugate-forming cells were CD 16-positive, and half of these were also positive for Leu 7. The CD 16 antigen disappeared from the cell surface during the effector:target interaction. T-cell markers were found on some of the conjugate-forming cells but not on the strongly bound effector cells. The NK cell function was directly proportional to the number of NK (CD 16) cells in the peripheral blood.