Interaction of Alveolar Macrophages with Nocardia asteroides: Immunological Enhancement of Phagocytosis, Phagosome-Lysosome Fusion, and Microbicidal Activity

Normal and specifically activated rabbit alveolar macrophages were infected in vitro with Nocardia asteroides GUH-2. In the presence of serum from normal rabbits, no significant differences were noted between normal and activated alveolar macrophages with respect to phagocytosis, incidence of phagosomelysosome fusion, or nocardicidal activity. However, all of these macrophage functions were enhanced by various immunological components. Serum from immunized rabbits enhanced phagocytosis of nocardial cells by activated macrophages, and there was an additional increase in phagocytosis observed when alveolar lining material was present. Complement had no effect on the ability of the macrophages to phagocytize nocardial cells. The greatest percentage of organisms phagocytized was observed when specifically primed lymph node cells, alveolar lining material, and serum from immunized rabbits were present in the incubation medium. N. asteroides GUH-2 inhibited phagosome-lysosome fusion in normal macrophages in the presence of serum from normal rabbits. However, addition of serum from immunized rabbits or the addition of specifically primed lymphocytes increased the amount of phagosome-lysosome fusion, whereas complement had no effect on this fusion process. Nocardial viability was not reduced when either normal or activated macrophages were infected with bacteria in the presence of normal serum, immune serum, or alveolar lining material. However, specifically activated macrophages incubated with primed lymph node cells obtained from immunized rabbits were able to both decrease the number of viable organisms recovered and to increase the incidence and extent of bacterial cell damage. The greatest number of organisms were killed by specifically activated macrophages when the bacterial cells were incubated with primed lymph node cells suspended in immune serum and alveolar lining material. These results indicate that activated macrophages alone are not sufficient to kill ingested N. asteroides GUH-2 and that specifically primed lymphocytes are important in host resistance to nocardial infections.