Researchers have found that particulate matter can knock the body’s immune system out of balance, promoting allergic inflammation.
A team at Pusan National University in South Korea exposed mice to PM10 and PM2.5 every day for 16 weeks before analysing lung tissue, plasma and immune cell profiles.
Compared to the control group, the exposed mice had inflamed and darkened lungs due to particle buildup. Their lung tissues showed clear signs of injury: increased inflammatory cells, thickened lung walls, and more proteins in lung fluid (an indicator of inflammation). These effects were worse in the PM2.5 group
The air pollution also triggered oxidative stress, an internal chemical stress that damages cells. The researchers found high levels of reactive oxygen species (ROS), oxidative DNA damage and cell death (apoptosis) in the lungs of exposed mice, along with a decrease in antioxidant activity. These harmful effects were seen in both PM10 and PM2.5 groups.
Interestingly, the team also saw that particulate matter had disrupted the balance of the immune system.
The immune system has different ways to deal with different kinds of threats. Two of the most important are TH1 responses which help attack viruses and bacteria, and TH2 responses which deal with parasites and allergens.
The study found that when mice were exposed to PM2.5, instead of staying in a healthy mix of TH1 and TH2 responses, their bodies moved toward a TH2-dominant state.
This is caused by part of the body’s natural defence system – a molecule called Nrf2.
When PM2.5 is inhaled, the stress it creates in the lungs activates Nrf2 to help protect against damage. However, in this study, the extra activation of Nrf2 didn’t just help with protection, it also changed how the immune system responded. Specifically, it pushed the immune system toward a TH2-type response, the kind of immune reaction linked to allergies and asthma.
So, instead of simply protecting the lungs, high Nrf2 activity seemed to accidentally encourage the type of immune response that makes asthma and other allergic conditions worse.
Additionally, particulate matter was seen to reduce the number of other immune cells that help defend against infections and cancer. This weakened immune function could explain why pollution exposure is especially harmful for people with asthma, COPD, or weakened immune systems.
Professor Changwan Hong from Pusan National University School of Medicine said: ‘This mechanistic link explains why air pollution can worsen asthma and other allergic diseases, identifying NRF2 as a key driver of this shift.
‘Our findings suggest that targeting oxidative stress or modulating NRF2 activity could be a new strategy to treat or prevent pollution-induced allergic inflammation, such as asthma.’
The full research can be read here.
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