Pulmonary host defenses in rabbits after immunization with Pseudomonas antigens: The interaction of bacteria, antibodies, macrophages, and lymphocytes

The development of humoral and cellular immunity in the lungs of rabbits was compared after intranasal and parenteral immunization with Pseudomonas antigens. The in vitro effect of respiratory antibodies and immune lymphocytes (to increase the phagocytosis of Pseudomonas by alveolar macrophages) was studied in order to understand further the intricate interactions of bacteria, opsonins, and activated macrophages in the lower respiratory tract. Intranasal immunization induced both IgG and secretory IgA agglutinating antibodies in respiratory secretions; however, the opsonic activity of IgG seemed superior to that of IgA in promoting macrophage phagocytosis. Immune respiratory lymphocytes, recovered from intranasally immunized rabbits, inhibited the migration of alveolar macrophages when stimulated with the immunizing antigen in direct assays of migration inhibition factor. However, this capacity lasted only two to three weeks and suggests that respiratory cellular immunity is transient after primary immunization and that frequent booster injections or persistent antigen contact may be necessary for maintenance of this cellular activity. In vitro activation of macrophages by immune lymphocytes did not increase macrophage phagocytosis of opsonized viable Pseudomonas or enhance bacterial killing.