Crucial mechanism driving colliding epidemics of smoking, TB unlocked by scientists

Tuberculosis spreads from person to person by inhaling infected droplets made when the TB sufferer coughs. The World Health Organization has designated TB a global emergency. Nine million people fall ill with TB each year, and it is the greatest killer worldwide due to a single bacterial infection. Many countries have recurring outbreaks and multi-drug resistant TB cases.

After infection most people do not become ill with TB, but immunosuppressed patients are susceptible. Smoking increases a person's susceptibility to infection by TB, risk of recurrence, mortality and persistent infectiousness. However, until now the exact reason or mechanism behind this connection between smoking and TB has been unknown.

The research team conducted the study with smokers, ex-smokers and non-smokers attending the bronchoscopy suite at St James's Hospital in Dublin. They found that the white blood cells located in the lungs of smokers and ex-smokers, which are responsible for fighting infections, showed a weakened response to the TB infection. In the smoker's lungs, these cells malfunction, and fail to make the chemical messengers that would normally fight the TB bacteria. In fact, the researchers found that these cells suppress the lungs' immunity after infection, which gives the TB bacteria a chance to take over.

Joseph Keane is Professor of Medicine at Trinity and St James's Hospital, HRB Clinician Scientist, and the senior author of the study. He said: "TB remains a huge global health problem, affecting millions worldwide. It has been known for some time that smokers are more susceptible to getting TB and nearly 80% of the world's one billion smokers live in countries of high TB prevalence. Therefore, while HIV is a key driver of the disease, numerically, smoking is more prevalent than HIV, making smoking the biggest global driver of the TB epidemic."

"This study provides evidence which explains the link between smoking and TB and should considerably strengthen anti-smoking efforts to control TB. However, the widespread emergence of multi-drug resistance TB means we badly need new therapy and vaccine options for TB. We are already applying the findings of this study to develop new treatment options."