Effect of systemic immunization on pulmonary clearance of Haemophilus influenzae type b.

The effect of systemic immunization on pulmonary clearance of Haemophilus influenzae type b (Hib) was studied in a mouse model system. Immunization of mice by intraperitoneal injection of viable Hib cells resulted in the appearance of Hib-directed antibodies in both serum and bronchoalveolar lavage fluid. The development of this Hib-directed antibody activity was associated with significant enhancement of early pulmonary clearance of Hib. Systemic immunization did not affect the recruitment of polymorphonuclear leukocytes to the alveoli, suggesting that the enhanced clearance of Hib observed in immunized animals was due to specific antibodies which promote either phagocytosis or extracellular killing of Hib. The spectrum of Hib-directed antibody specificities detected in sera from immunized animals was essentially identical to that detected in bronchoalveolar lavage fluids from these same animals. Similarly, intravenous administration of an immunoglobulin G monoclonal antibody specific for Hib lipopolysaccharide resulted in the subsequent appearance of this antibody in the alveolar spaces where it enhanced pulmonary clearance of Hib. This study shows that this mouse model system can be used to measure the effect of both active and passive immunization on the clearance of Hib from the lower respiratory tract.