Researchers from the University of Liverpool, Queen Mary University, London and Trinity College Dublin have linked exposure to diesel exhaust particles (DEPs) to susceptibility to pneumococcal disease. An open-access paper on the work is published in the Journal of Allergy and Clinical Immunology.

The World Health Organization (WHO) estimates that air pollution is responsible for 7 million deaths per year, with 7% of these attributable to pneumonia. Many of these fatalities have been linked to exposure to high levels of airborne particulates, such as diesel exhaust particles (DEPs).

The bacterium Streptococcus pneumoniae is the most common cause of pneumonia and meningitis and the leading cause of infectious disease deaths in under-5s and elderly groups worldwide. In the majority of healthy people, this bacterium lives harmlessly in the back of the nose and throat without causing any symptom. However, if the pneumococcus gains access to normally sterile sites in the body, such as the lungs and blood, it has the potential to cause life-threatening diseases.

The researchers sought to determine whether exposure to DEPs could promote the progression of asymptomatic nasopharyngeal carriage of Streptococcus pneumoniae to invasive pneumococcal disease.

The researchers, led by Professor Aras Kadioglu from the University of Liverpool’s Institute of Infection & Global Health, used a combination of mouse models and lab-based assays in both mouse and human cells to provide insight into the link between DEP exposure and pneumococcal disease.

The researchers found that following exposure to DEPs, airway macrophages, which are key immune cells for controlling bacterial infections and removing debris from the body, become congested with DEPs, reducing their ability to kill the pneumococcus.

from Shears et al.

This allows the bacteria to survive more easily in the airways, invade the lungs, and cause significant inflammation, which eventually leads to bacterial translocation into blood, thereby causing severe disease.

We know that exposure to air pollution is harmful, responsible for millions of deaths every year, of which a significant proportion is due to pneumonia. What we did not know however, was how pollution, such as diesel exhaust particles, actually causes airway disease. In this study, we have now discovered the cellular mechanisms behind this. Our study highlights an urgent need to tackle airway pollution if we are to reduce life threatening respiratory diseases such as pneumonia.

—Professor Aras Kadioglu

Our study shows that exposure to DEPs, which is a major airborne particulate pollutant both here in the UK and abroad, may be one of the key factors involved in the switch from harmless pneumococcal colonisation of the nasal tissues to severe disease, such as pneumonia.

Our data provides further insight to support previous observations of increased pneumonia hospital admissions in countries such as China, where airborne pollution levels are highest.

The reduced ability of DEP exposed airway macrophages to control the infection appears to be key in the increased number of cases of pneumococcal disease. This study adds further impetus to reduce global pollution levels.

—Dr Rebecca Shears, first author

Resources

• Shears, Rebecca K. et al. (2020) “Exposure to diesel exhaust particles increases susceptibility to invasive pneumococcal disease” Journal of Allergy and Clinical Immunology doi: 10.1016/j.jaci.2019.11.039