Clearance of bacteria from lungs of mice after opsonising with IgG or IgA

The clearance of organisms from the lungs of mice was followed after aerosol administration. Preopsonisation of the organisms with immune serum, as a source of specific antibody, enhanced the rate of pulmonary clearance while s.IgA delayed clearance. In the peritoneal cavity, bacteria pre-treated with immune serum were cleared more rapidly than unopsonised bacteria, but s.IgA had little effect. The presence of Fc receptors for IgG and not s.IgA on alveolar macrophages suggests that, in secretions, IgG is the predominant antibody promoting phagocytosis by alveolar macrophages and that any protective effect of s.IgA is not mediated by these cells.