The effect of local antibody responses on in vivo and in vitro phagocytosis by pulmonary alveolar macrophages.

This study used both in vitro and in vivo techniques to determine if local antigen deposition in the lung has a localized effect on immune phagocytosis by pulmonary alveolar macrophages (PAM). Using a fiberoptic bronchoscope, dogs were immunized in the left cardiac and left diaphragmatic lobes with sheep red blood cells (sRBC). The right cardiac and right diaphragmatic lobes of the same animals received saline as controls. Unimmunized dogs served as additional controls. On days 2, 6, 9, 13, and 16 after immunization, the left and right diaphragmatic lobes were lavaged, and the cells and fluids were analyzed in vitro. Opsonizing antibody in lavage fluids was first detectable at 6 days, peaked at 9-13 days, and was significantly higher in the immunized lobe than in the control lobe. Phagocytosis of sRBC caused by cytophilic antibody on PAM also peaked at 9 to 13 days. Significantly more cytophilic antibody activity was detected on day 9 in the immunized lobes, than in the control lobes. In vivo phagocytosis of sRBC was evaluated in the alveoli of immunized and control lobes of immunized dogs and a control lobe of unimmunized dogs. Phagocytosis of sRBC by PAM in the immunized lobes was about four times greater than that of the control lobes and about 40 times greater than that of a control lobe of an unimmunized dog. These results indicate that the local deposition of a particulate antigen in the lung had a localized effect on immune phagocytosis. These data suggest that the accumulation of antibody-secreting cells in the alveolus may play a critical role in pulmonary defense mechanisms.