The diminished power of the immune system in older adults is usually blamed on the aging process.
In a study from Columbia University, scientists found that decades of particulate air pollution also take a toll.
They found that inhaled particles from environmental pollutants accumulate over decades inside immune cells in lymph nodes associated with the lung, eventually weakening the cells’ ability to fight respiratory infections.
The findings offer a new reason why individuals become more susceptible to respiratory diseases with age.
Elderly people are especially vulnerable to respiratory infections, a fact brought into stark relief by the COVID pandemic.
The death rate from COVID is 80 times greater in people over age 75 than in younger adults, and the elderly are also more vulnerable to influenza and other infections of the lung.
More than ten years ago, the team began to collect tissues from deceased organ donors to study immune cells in multiple mucosal and lymphoid tissues.
Such cells have been largely inaccessible to researchers studying the immune system where sampling is limited to peripheral blood.
As the researchers collected more tissue from younger donors, they also noticed an age difference in the appearance of the lung’s lymph nodes:
Those from children and teenagers were largely beige while those from donors over age 30 looked were tinged with black and got darker with increasing age.
In the new study, the team examined tissues from 84 deceased human organ donors ranging in age from 11 to 93, all non-smokers.
They found that the pollutant particles in the lung’s lymph nodes were located inside macrophages, immune cells that engulf and destroy bacteria, viruses, cellular debris, and other potentially dangerous substances.
The macrophages containing particulates were significantly impaired: they were much less capable of ingesting other particles and producing cytokines—chemical “help” signals—that activate other parts of the immune system.
Macrophages in those same lymph nodes that did not contain particulates were unimpaired.
The team says pollution undoubtedly plays a role in creating more dangerous respiratory infections in elderly individuals and is another reason to continue the work in improving air quality.
These findings underscore the importance of additional research to better understand the lung effects of inhaled particulates and the interactions between air pollution and chronic lung diseases.
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The study was conducted by Donna Farber et al and published in Nature Medicine.
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