A new investigation by a group of researchers from Trinity College Dublin, the University of Liverpool, and Queen Mary’s University in London shows that exposure to diesel exhaust particles (DEPs) can increase a person’s chances of contracting pneumococcal disease. The research has been published in the Journal of Allergy and Clinical Immunology.
The principal cause of meningitis and pneumonia is the bacterium Streptococcus pneumoniae. It is the primary source of infectious disease deaths in people under five years old and elderly groups worldwide. For most healthy people, the bacterium lives harmlessly in the back of the nose and throat. Things go wrong when the pneumococcus migrates to normally sterile sites in the body, such as the lungs and blood. There, it has the potential to cause deadly diseases.
Prof Aras Kadioglu from the University of Liverpool’s Institute of Infection & Global Health led the team. Their goal was to find out more regarding the conditions that allow this ordinarily harmless bacterium to progress into such severe invasive diseases. Hence, they began by examining the role of DEPs in the development of pneumococcal disease. Air pollution was an appropriate condition to concentrate on, seeing as the World Health Organisation (WHO) estimates approximately 7 million people die annually from air pollution – and 7% of these are attributable to pneumonia.
DEPs constitute a significant component of air pollution in many parts of the world. Approximately 37% of the world’s population reside in regions where levels of airborne pollution, such as DEPs, exceed WHO guideline limits. What are DEPs exactly? They are the particulate matter component of diesel exhaust, which involves diesel soot, as well as aerosols such as ash particulates, sulfates, silicates, and metallic abrasion particles.
The Study
A combination of lab-based assays and mouse models was used. Both human and mouse cells were analyzed to provide insight into possible connections between DEP exposure and pneumococcal disease.
The Results
Airway macrophages – the body’s vital immune cells for controlling bacterial infections and removing debris – become congested with DEPs if exposed to them. This blockage of particles reduces the macrophages ability to kill the pneumococcus.
As a result, the bacteria can survive easily in the airways and move on to invade the lungs, where they cause significant inflammation. From there, the bacteria translocate into the blood, where they cause severe disease.
Professor Kadioglu said:
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.
Dr. Rebecca Shears, first author of the study, added:
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 colonization of the nasal tissues to severe diseases, such as pneumonia.
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.
Their findings provide additional insight to support previous observations of increased pneumonia hospital admissions. For example, in countries with poor air quality such as China, where airborne pollution levels are highest.
