Phagocytosis and killing of Haemophilus influenzae by alveolar macrophages: no difference between smokers and non-smokers.

The susceptibility of smokers to pneumonia caused by Haemophilus influenzae may result from impairment of phagocytic or bactericidal function of pulmonary alveolar macrophages (PAM). We compared ingestion and killing of non-typable H. influenzae and H. influenzae type B by alveolar macrophages from asymptomatic smokers and non-smokers. Three times as many cells were recovered from bronchoalveolar lavage of smokers. Non-typable H. influenzae (NTHI) were phagocytosed and killed readily by PAM from both groups of subjects, while H. influenzae type B were resistant to phagocytosis. No difference in uptake of bacteria was detected between PAM of smokers and non-smokers. PAM from smokers had a slightly greater bactericidal activity than PAM from non-smokers. These results suggest that other host factors, such as impaired tracheobronchial clearance or the presence of conditions that favor bacterial growth rather than damage to alveolar macrophages, are responsible for the susceptibility of smokers to Haemophilus infections.