Pulmonary Clearance and Phagocytic Cell Response to Normal Pharyngeal Flora1–3

Because human lungs are repetitively inoculated with the normal bacterial flora of the pharynx, we determined the pulmonary clearance of representative species after aerosol inoculation of a murine model, and characterized the phagocytic cell response by bronchoalveolar lavage. Viable bacteria remaining in the lungs at 1, 2, and 4 h were: Streptococcus sanguis, 24%, 8%, and 1%; Streptococcus salivarius, 49%, 24%, and 5%; Neisseria catarrhalis, 69%, 49%, and 22%. Clearance of Streptococcus sanguis was associated with a twofold increase in alveolar macrophages (p < 0.05);Streptococcus salivarius evoked a doubling of alveolar macrophages and a 20-fold rise in granulocytes (p < 0.05); the response to Neisseria catallhalis was a 400-fold increase in granulocytes (p < 0.05).Thus, normal pharyngeal organisms are cleared rapidly from the lung by a dual phagocytic cell system. It is speculated that bacteria-phagocyte interaction allows the possibility of lung injury from proteolytic enzymes released from either se...