Polymorphonuclear leukocyte, T-lymphocyte, and natural killer cell activities in elderly nursing home residents

Senescence and cytokines modulate the NK cell expression

We have been investigating senescence-related changes in human peripheral blood natural killer (NK2) cells. Data accumulated so far consistently and clearly show that both basal and cytokine (IL-2 and interferon alpha and gamma) induced antitumor MHC-unrestricted cytotoxic activity of NK cells are well-preserved in the healthy elderly. To investigate if the non-cytotoxic functions of NK cells are also spared from the influence of senescence, recombinant IL-2-inducible secretion of IFN-gamma, which serves as a first line of defense, was examined. The amount of IFN-gamma secreted by purified, 18 h activated NK cells from the elderly was only 25 percent of that released by the cells from the young. Thus, the type 1 cytokine-inducible cytotoxic and cytokine secretory functions appear to be dissociable properties of NK cells, at least in the elderly. However, this aging-related early phase secretory deficit could be overcome by chronic stimulation with IL-2 (7 day culture). Since different subsets could perform different functions, we analyzed the NK subsets by flow cytometry. A minor CD56bright subset and a major CD56dim subset could be distinguished based on the density of expression of the cell surface CD56 molecule (N-CAM). We inquired if immunosenescence is likely to impact the steady-state level of circulating NK subsets. A significant decrease (P < 0.01) in percent CD56bright among CD56+ cells was observed in the elderly with a relative sparing of the CD56dim subset. The CD56bright/CD56dim ratio, perhaps representing NK cell maturity status, declined with age. This maturation-related subset redistribution and partial loss during aging of high affinity IL-2 alpha beta gamma receptor bearing 'immature' CD56bright NK cells has not been reported before. It could be a consequence of the decline in the level of IL-2 during aging. It is concluded that post-adolescent age-associated modulations in human NK cells are not expressed uniformly; they are pronounced in some, subtle in others but negligible in yet other biological parameters.

Neutrophil function in elderly persons assessed by flow cytometry

It is well known that the immune response declines with senescence and it is suggested that these changes render an individual susceptible to infection, autoimmune phenomena and cancer. Bacterial and viral infections are a major cause of illness and death amongst aged subjects, and once infection is established, the elderly also have a diminished capacity to prevent its spread (1). The cellular and molecular basis for this age-related decline in immunocompetence are still unknown and, possibly, are related to an alteration in cell transduction mechanisms (2).