MedWire News: Cigarette smoke selectively augments the airway and alveolar inflammatory and remodeling responses induced in lungs by viral pathogen-associated molecular patterns (PAMPs) and viruses, a study in mice reveals.

The findings could explain why the cold and influenza virus symptoms that are often mild and transient in non-smokers are often much more severe in smokers, the authors suggest in the Journal of Clinical Investigation.

Smokers are more likely to die during influenza epidemics than non-smokers and are more prone to chronic obstructive pulmonary disease (COPD), leading many researchers to propose that cigarette smoke decreases anti-viral responses.

However, Jack Elias (Yale School of Medicine, New Haven, Connecticut, USA) and colleagues found evidence to support that the opposite is in fact true.

They investigated the effects of cigarette smoke on PAMP-induced pulmonary inflammation and remodeling in mice, and found that cigarette smoke enhanced parenchymal and airway inflammation and apoptosis induced by the viral PAMP poly(I:C), and also induced accelerated emphysema and airway fibrosis.

The mice's immune system cleared the virus normally, but the exaggerated inflammation caused increased levels of tissue damage.

"The anti-viral responses in the cigarette smoke exposed mice were not only not defective, but were hyperactive," said Elias. "These findings suggest that smokers do not get in trouble because they can't clear or fight off the virus; they get in trouble because they overreact to it."

"If the exaggerated responses are verified in human studies, it will be the first explanation for why viral infections are more serious in smokers," commented Elias. "Once verified, we can find ways to prevent the destruction of lung tissue and the higher illness and death among smokers."

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