Age-associated alterations in human natural killer cells. 1. Increased activity as per conventional and kinetic analysis

We report a positive association between the human peripheral blood natural killer (NK) cell activity and the age (20-94 years) of 137 healthy volunteers. Irrespective of the methods of data representation, the elderly (greater than 80 years) express a statistically significant (at 0.001 level) higher (35-80.7%) mean NK activity when compared to younger adults (less than 40 years). Results of repeat assays and paired assays support a similar conclusion. This difference can be demonstrated at a wide range of effector or target cell concentrations or times of assay and is not influenced by in vivo lymphocyte count. Single-cell assay results suggest that an increase in the frequency of NK cells may be responsible for the higher NK activity in the elderly. These findings were confirmed by an enzyme-like kinetic analysis. Vmax, the maximum cytotoxic potential of the lymphocytes from the elderly, is nearly four times higher than that of younger adults. It is concluded that unlike the age-related general decline in T- and B-cell reactivity (as demonstrated here with concanavalin A and pokeweed mitogen), the NK cell system is highly active in a majority of the healthy elderly.