If you’ve spent decades living in a polluted city, there’s a strong chance your lymph nodes will become visibly riddled with black particles, impairing your immune system’s ability to fight off disease.
To understand the impact of air pollution on the immune system, scientists from Columbia University carried out an autopsy of 84 people’s lymph nodes. This included people within the huge age range of 11 to 93 years, all of whom were non-smokers.
When examining the older people who had been exposed to air pollution for longer, the researchers discovered that their lymph nodes had literally turned black as a result of breathing decades of dirty air.
Lymph nodes from children and teenagers tended to be a pinky-beige color – but those from donors over 30 years old began to become tinged with black, becoming increasingly darker as the donors aged.
"When we looked at people's lymph nodes, we 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," Donna Farber, lead study author and professor of microbiology & immunology at Columbia University Vagelos College of Physicians and Surgeons, said in a statement.
"When we imaged the lung's blackened lymph nodes and found they were clogged with particles from airborne pollutants, we started to think about their impact on the lung's ability to fight infection as people age," added Farber.
Lymph nodes are bean-sized organs found throughout the body. They are important hubs of the adaptive immune system, filtering the body’s lymphatic fluid which helps rid the body of germs and remove waste products. For this study, the team specifically looked at the lymph nodes close to the lungs since they were dealing with inhaled air pollution.
Just as you’d no doubt expect from lymph nodes chock-full of black pollutant particles, the researchers found evidence that their ability to ward off infections and disease was hampered.
The dark pollutant particles were found inside the lymph node’s macrophages: a type of immune cell that engulfs bacteria, viruses, cellular debris, and other foreign invaders. This left them less capable of ingesting other particles and reduced their ability to produce cytokines, proteins that act as chemical "help" signals.
"These immune cells are simply choked with particulates and could not perform essential functions that help defend us against pathogens," explained Farber.
While it’s hardly ground-breaking news that air pollution is bad for your health, the researchers believe their work clearly highlights how air pollution can contribute to elderly people’s ability to fight off respiratory infections, whether it’s COVID-19 or a common cold.
The study was published in the journal Nature Medicine.