Researchers in Trudeau Institute in Saranac Lake, New York have identified a potential target that could help boost immune system function in older individuals.
The decreases in immune system function that accompany aging leave elderly individuals more susceptible to numerous infectious agents than younger people.
Thus many vaccines now in use are not nearly as effective in protecting older people.
Previous study has shown that a specific type of immune cells, called CD4 T cells, which are critical to vaccine response, become less effective with age.
Robust CD4 activity is necessary for antibody production in response to infection or vaccination.
Specifically, naive CD4 T cells, those that have not come into contact with or become specialized to respond to a particular pathogen, are needed to ensure protection against new pathogens as well as vigorous responses to vaccination.
In the new study, lead researcher Susan Swain and her colleagues showed that naive CD4 T cells from older mice survived longer than the corresponding cells from young mice when transplanted into normal intact hosts.
This finding helps to explain how older animals maintain populations of circulating CD4 T cells, even though generation of new cells in the thymus decreases dramatically with age.
The Trudeau team demonstrated that the older cells were relatively resistant to cues that trigger a process known as apoptosis (from the Greek "falling leaves"), a type of orchestrated cell death, and that these cells contained lower levels of a molecule that promotes apoptosis.
But even though aged CD4 T cells enjoy longer lives, their function decays.
Since age exposes cells to increasing levels of stressors such as oxidative damage (aka "free radicals") that promote changes associated with cancer, the authors speculate that the strategy of maintaining CD4 cell numbers by increasing the life spans of individual cells rather than by promoting proliferation of new cells may be a safeguard of sorts against tumor development.
The study appears in Proceedings of the National Academy of Sciences.