Exposure to cigarette smoke may impair the ability of immune cells to clear bacterial infections from the lungs, specifically nontypeable Haemophilus influenzae (NTHI), a pathogen often associated with respiratory infections and the progression of respiratory diseases.
The researchers from Spain and the United Kingdom report their findings in the October 2009 issue of the journal Infection and Immunity.
NTHI, commonly found in the human respiratory tract, may remain asymptomatic in healthy individuals or it can cause invasive diseases such as meningitis, sinusitis, pneumonia, and bronchitis. It is also the pathogen most frequently isolated in the respiratory tract of patients with chronic obstructive pulmonary disease (COPD) and chronic bronchitis. Alveolar macrophages are part of the lungs' innate defense system and they play an essential role in the clearance of bacterial infections. Prior associations between cigarette smoke and respiratory infections caused by NTHI have been established and now researchers are hypothesizing that cigarette smoke may disrupt the capability of alveolar macrophages to clear NTHI from the lungs.
In the study researchers first examined the interaction between NTHI and alveolar macrophages and found that the macrophages adhere to and ingest NTHI, a process known as phagocytosis. Researchers also observed the effect of cigarette smoke in macrophage cell lines and human alveolar macrophages obtained from smokers and patients with COPD and found that cigarette smoke extract impaired the alveolar macrophage process. Additionally, cells exposed to cigarette smoke extract were treated with glucocorticoid, an anti-inflammatory drug commonly used to treat respiratory conditions, and results showed that the drug did not compensate for the impairment to the alveolar macrophage process caused by the cigarette smoke.
"This study revealed novel effects of cigarette smoking on alveolar macrophage physiological functions which could contribute to lung bacterial colonization by opportunistic pathogens, such as NTHI," say the researchers.
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