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Decades of air pollution undermine the immune system, lymph nodes study finds
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
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Aged biomass emissions could pose greater risk to lungs than fresh wildfire smoke
Biomass burning—whether from wildfires, wood stoves or agricultural fires—sends massive amounts of tiny particles and chemicals into the air. These emissions are not just an environmental issue; they pose serious health risks, especially for our lungs.
An Environmental Pollution study reveals how two key components of biomass smoke—levoglucosan and 4-nitrocatechol—affect human lung cells. Their findings suggest that aged smoke, which has undergone chemical changes in the atmosphere, could be even more dangerous than fresh smoke.
Biomass burning refers to the combustion of organic materials like wood, leaves and crop residues. This process releases large amounts of carbon-based aerosols, which contribute to air pollution. Among the many chemicals produced in the smoke, levoglucosan and 4-nitrocatechol serve as important markers.
Levoglucosan is a sugar-like compound released when wood burns, while 4-nitrocatechol forms when smoke interacts with nitrogen oxides in the atmosphere, a process known as chemical aging. While scientists have long studied the environmental effects of biomass burning, less is known about how these compounds directly impact human health.
Researchers used two different types of lung cells: BEAS-2B cells, which represent normal lung-lining cells, and A549 cells, which come from lung cancer tissue and are commonly used in respiratory studies. The researchers exposed these cells to different concentrations of levoglucosan and 4-nitrocatechol over 24 and 48 hours. They then measured cell survival, stress levels and signs of damage to the cells' mitochondria—the "power plants" of cells that generate energy.
Their key findings were that aged smoke is more toxic:
The study found that 4-nitrocatechol was significantly more toxic to lung cells than levoglucosan. At relatively low doses, 4-nitrocatechol reduced cell survival and caused oxidative stress—an imbalance that damages cells and can lead to lung diseases.
Exposure to 4-nitrocatechol disrupted the function of mitochondria in lung cells, leading to a process called apoptosis, or programmed cell death. This damage could contribute to long-term lung problems.
While levoglucosan exposure also led to cellular stress, its effects were much less severe compared to 4-nitrocatechol. Cells exposed to levoglucosan showed signs of mitochondrial stress, but they were able to recover over time.
Since 4-nitrocatechol forms when biomass smoke reacts with urban air pollutants like nitrogen oxides, areas affected by both wildfires and traffic pollution may be particularly at risk.
While wearing an N95 or P100 mask can help filter out fine particles, it may not fully protect against toxic gases and chemicals present in aged smoke. Here are some steps individuals can take:Use HEPA air purifiers to remove fine particles from indoor air, and keeping windows and doors closed can help minimize smoke infiltration.
Ensure that homes are properly sealed to prevent smoke from entering through cracks, vents or poorly fitted windows and doors; avoid using candles, gas stoves or burning wood indoors, as these can add to indoor air pollution;
In extreme conditions, individuals with respiratory issues or prolonged exposure may consider investing in gas masks with activated carbon filters, which can help remove both particles and harmful gases.
If air quality levels are hazardous and exposure is prolonged, relocating to an area with cleaner air—either indoors with filtered ventilation or to a different location—might be the safest option.
This study reinforces concerns that exposure to biomass smoke—especially aged smoke containing 4-nitrocatechol—can have serious health consequences.
Long-term exposure to these pollutants has been linked to respiratory diseases such as asthma, chronic obstructive pulmonary disease and lung cancer. People who live in wildfire-prone areas or who frequently burn wood for heating should take extra precautions, say the researchers.Faria Khan et al, Evidence for cytotoxicity and mitochondrial dysfunction in human lung cells exposed to biomass burning aerosol constituents: Levoglucosan and 4-nitrocatechol, Environmental Pollution (2024). DOI: 10.1016/j.envpol.2024.125173
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