Impairment of polymorphonuclear leukocyte immigration as a mechanism of alcohol-induced suppression of pulmonary antibacterial defenses

Antibacterial defenses of the lung against pathogens involved in alcohol-related bacterial pneumonias include the alveolar macrophage and polymorphonuclear leukocytes (PMN) that migrate into the lung to provide auxiliary phagocytic defenses. Alcohol is known to impair PMN migration; failure of PMN to appear in the lungs may be related to lowered host resistance. To test this hypothesis mice were challenged by aerosol inhalation with Staphylococcus aureus or Proteus mirabilis and injected intraperitoneally with increasing doses of alcohol (0.25, 0.5, and 1.0% body weight). Intrapulmonary killing of the organisms was quantitated at 4 h thereafter, at which time quantitative differential counts were also performed on lavaged cell populations. Alcohol treatment increasingly suppressed the killing of S. aureus, so that at the highest dose, 41.5 ± 4.2% of the initial viable bacteria remained as compared with 11.9 ± 0.7% in the lungs of untreated animals. In contrast, the high dose of alcohol totally ablated pulmonary antibacterial defenses against gram-negative bacteria, allowing the proliferation of P. mirabilis to 117.1 ± 4.5%, the control values being 17.9 ± 1.7%. The immigration of PMN into the lung airways that characterized inhalation challenge with P. mirabilis was also inhibited by alcohol in a dose-dependent manner. From the lungs of untreated animals 4.0 ± 0.7 x 10⁶ PMN were retrieved as compared with 1.1 ± 0.2 x 10⁶, 7.1 ± 0.7 x 10⁵, and 1.1 ± 0.2 x 10⁵, respectively, with the increasing doses of alcohol. These data indicate that inhibition of PMN immigration to the lungs to provide auxiliary phagocytic capabilities may be one mechanism by which alcohol intoxication suppresses pulmonary antibacterial defenses.