Role of C5 and recruited neutrophils in early clearance of nontypable Haemophilus influenzae from murine lungs

We used a mouse model system to investigate the pulmonary defense mechanisms involved in clearance of nontypable Haemophilus influenzae from the lower respiratory tract. The importance of the C5 complement protein molecule in polymorphonuclear leukocyte (PMN) recruitment was studied by using congenic C5-sufficient B10.D2/nSn (C5⁺) and C5-deficient B10.D2/oSn (C5^-) mice. The C5⁺ and C5^- mice were inoculated with saline or nontypable H. influenzae via an endobronchial catheter. Clearance of bacteria was studied by using quantitative lung cultures. Bronchoalveolar lavage was performed at several time intervals. The number of cells in the lavage fluid were counted, and chemotactic activity was assayed in lavage fluid by the leading front technique, using human PMN in modified Boyden chambers. Pulmonary clearance of bacteria was significantly impaired in the absence of C5 (P < 0.05). The C5⁺ mice recruited significantly more PMN after challenge with nontypable H. influenzae than C5^- mice did (P < 0.05), but significant PMN recruitment occurred in C5^- mice. Similarly, although chemotactic activity was present in both C5⁺ and C5^- mice, significantly more intraalveolar chemotactic activity was noted in C5⁺ mice than in C5^- mice (P < 0.05). The C5 molecule yields important chemotaxins during this early time period, but other chemotaxins are also present within the alveoli, demonstrating the redundancy of the inflammatory response after pulmonary challenge with nontypable H. influenzae. Nitrogen mustard-induced neutropenic animals were studied to evaluate the functional importance of PMN in pulmonary clearance of nontypable H. influenzae. Pulmonary clearance of nontypable H. influenzae was significantly impaired in neutropenic animals (P < 0.05). Our results indicate that the prompt appearance of PMN in lungs is crucial for early clearance of nontypable H. influenzae.