Natural Killer Cell Numbers Increase with Age
The immune system ages in ways that are harmful to tissue function and health, becoming both less effective and overly inflammatory. Not all of the observed changes in immune cell activities and immune cell population sizes are harmful, however. Some are compensatory, even though this compensation isn't enough to stop the overall decline. With that in mind, researchers here report on an analysis of the size of immune cell populations in old individuals, including centenarians. They find that natural killer cells increase in number with age, which they characterize as an adaptation to the aged environment.
The immune system of semi-centenarians and super-centenarians (i.e., the oldest centenarians) is believed to have peculiar characteristics that enable them to reach extreme longevity in a relatively healthy state. Therefore, in previous papers, we investigated, through flow cytometry, variations in the percentages of the main subsets of αβ T cells and γδ T cells in a Sicilian cohort of 28 women and 26 men (age range 19-110 years), including 11 long-living individuals (older than 90 years) and 8 oldest centenarians. These investigations suggested that some observed immunophenotypic changes may contribute to the extreme longevity of the oldest centenarians.
In the present study, to further characterize the immunophenotype of the oldest centenarians, we examined the percentages of Natural Killer (NK) cells identified as CD3-CD56+CD16+ in the previously described Sicilian cohort. We found a highly significant increase in NK cell percentages with age. When stratified by gender, this significant increase with age was maintained in both sexes, with higher significance observed in males.
Our findings on NK cells, together with the previously obtained results, discussed in the context of the literature, suggest that these changes are not unfavourable for centenarians, including the oldest ones, supporting the hypothesis that immune aging should be considered as a differential adaptation rather than a general immune alteration. These adapted immune mechanisms allow the oldest centenarians to successfully adapt to a history of insults and achieve remarkable longevity.