These studies compared the ability of specific secretory IgA (sIgA) and IgG antibodies to promote phagocytosis of viable Pseudomonas aeruginosa by human alveolar macrophages. Macrophages were obtained by lung lavage of normal adult smoker and nonsmoker volunteers and were maintained as in vitro cell monolayers. Both immune sIgA and IgG agglutinating antibodies were demonstrated to coat and opsonize viable bacteria, whereas similar nonimmune immunoglobulin preparations did not. When alveolar macrophages were challenged with viable opsonized 14C labeled Pseudomonas, IgG reacted bacteria were ingested better and killed more readily than sIgA opsonized organisms. Phagocytic responses were not significantly different between macrophages obtained from smokers and nonsmokers. Although sIgA and IgG antibodies can be found in respiratory secretions and both are undoubtedly important in pulmonary host defense, IgG opsonic antibody was superior in enhancing the uptake of Pseudomonas by in vitro cultured alveolar macrophages. It may be the more important respiratory antibody for certain bacterial infections.
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