Pulmonary Host Defenses

The opsonic properties of immune bronchial secretions and IgA and IgG antibodies separated from them were assessed in an in vitro alveolar macrophage system for their effect on phagocytosis and intracellular killing of Pseudomonas aeruginosa. Although IgA and IgG antibodies had specific agglutinative activity, IgG had superior opsonizing properties when compared with IgA. Also, it seemed to be the principal opsonin in normal respiratory secretions. Immune IgG whether isolated from bronchial fluid or serum was indistinguishable in its opsonic activity; however, the intact IgG molecule was required for optimal function. Opsonins specifically facilitated the phagocytosis of bacteria by macrophages; once ingestion had occurred, intracellular killing of Pseudomonas organisms was rapid and seemingly unrelated to the immune status of the opsonins.