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The diminished power of the immune system in older adults is usually blamed on the aging process. But a new study by immunologists shows that decades of particulate air pollution also take a toll.
The study 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—published Nov. 21 in Nature Medicine—offer a new reason why individuals become more susceptible to respiratory diseases with age.
Lung lymph nodes from six non-smokers between the ages of 20 and 62. Particles of air pollution darken the lymph nodes and impair immune cells within the nodes. Credit: Donna Farber / Columbia University Irving Medical Center
The work started more than ten years ago, when the researchers 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.
When they looked at people's lymph nodes, they were struck by how many of the nodes in the lung appeared black in color, while those in the GI tract and other areas of the body were the typical beige color.
And 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.
When they imaged the lung's blackened lymph nodes and found they were clogged with particles from airborne pollutants, they started to think about their impact on the lung's ability to fight infection as people age.
In the new study, the researchers examined tissues from 84 deceased human organ donors ranging in age from 11 to 93, all nonsmokers.
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.
These immune cells are simply choked with particulates and could not perform essential functions that help defend us against pathogens.
This study shows that 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.
Basak B. Ural et al, Inhaled particulate accumulation with age impairs immune function and architecture in human lung lymph nodes, Nature Medicine (2022). DOI: 10.1038/s41591-022-02073-x