Diesel exhaust particles can disturb the function of human brain immune cells, known as microglia, according to a recent study led by the University of Eastern Finland. The findings, published in Environment International, shed light on how traffic-related air pollution could contribute to brain inflammation and neurodegenerative diseases.

Using human induced pluripotent stem cell–derived microglia (iMGLs), the team examined how particles from different diesel engines and fuels affect these critical immune cells. The results were striking: particles from engines with older emission control technology caused extensive transcriptional and functional changes in microglia, while particles from renewable diesel used in modern Euro 6–compliant cars had only minor effects.

Microglia play a vital role in clearing cellular waste and maintaining brain homeostasis. Disruption of these processes can lead to chronic neuroinflammation and increase the risk of neurodegenerative diseases.

“Microglia are the brain’s first line of defence,” says Dr Sohvi Ohtonen, the first author of the study. “We observed that particles from diesel engines with older emission technology significantly impaired microglial functions, including waste clearance and inflammation control. Although modern filtration systems reduce these harmful effects, traffic-related pollution remains a serious health concern.”

Diesel particles rich in black carbon and polycyclic aromatic hydrocarbons (PAHs) activated stress and immune signalling pathways such as TREM1 and Toll-like receptor signalling. The affected microglia showed impaired lysosomal function and phagocytosis, key processes that keep the brain environment healthy.

While modern emission control technology appears to mitigate the most harmful effects on microglia, the study highlights that long-term exposure to diesel pollution could increase the risk of neuroinflammation and neurodegenerative disease through chronic alterations in microglial activity.

This project has received funding from the European Union's Horizon 2020 and MSCA COFUND programmes, the Research Council of Finland and Päivikki and Sakari Sohlberg Foundation. The Czech partners received funding from the Ministry of Education, Youth and Sports of the Czech Republic and the European Structural and Investments Funds.

Publication

Ohtonen, S., et al. (2025). Traffic-related diesel pollution particles impair the lysosomal functions of human iPSC-derived microglia. Environment International, 199, 109467. https://doi.org/10.1016/j.envint.2025.109467