Increased killer cell activity in aged humans.

Natural cell-mediated cytotoxicity (NCMC) against a cell line (K-562) and antibody-dependent cellular cytotoxicity (ADCC) against the same target and against chicken red blood cells were investigated in two age groups (20--45 and 70--98 years old). Proliferative response to PHA and to allogenic cells as well as some subpopulation determinations were also carried out only lymphocytes of the same subjects. In contrast to the significantly decreased proliferative responses, NCMC showed a moderate, and the two ADCC values a highly significant increase in the group of aged subjects. These increased values showed some similarities with the quantitative changes within the T-lymphocyte subpopulations. The incidence of serum samples of NCMC inhibitory activity was only moderately increased in the group of aged subjects as compared to that of the young individuals. On the basis of these results, we concluded that the immune system of healthy aged subjects seems altered or inbalanced rather than depressed to that of the young individuals.