Natural killer cells in healthy aging.

Immunosenescence is a process that affects all cell compartments of the immune system. Age-associated changes have been demonstrated not only on T lymphocytes but also in different aspects of the innate immunity including natural killer (NK) cells. A significant expansion in the percentage of NK cells showing a mature phenotype has been found in healthy elderly donors, and the NK-cytotoxic capacity of total peripheral blood lymphocytes is well preserved in these individuals. However, NK-cell killing of K562 is impaired when considered on a per-cell basis. Furthermore, NK cells from elderly people show a decreased proliferative response to interleukin 2 and a parallel impaired expression of the CD69 activation antigen. The response to interleukin 2 of NK cells from aged donors is also impaired in terms of their capacity to kill NK-resistant cell lines, but not when K562 killing, perforin synthesis, or tumor necrosis factor alpha production are considered. Therefore phenotypic and functional alterations can be shown in NK cells in healthy aging. These changes are compatible with the expansion of a mature NK subset.