Induction of phagocytic inhibitory activity in cats with chronic Pseudomonas aeruginosa pulmonary infection.

Chronic pulmonary infection has been established in cats by repeated intrapulmonary inoculation of viable Pseudomonas aeruginosa enmeshed in agarose beads. In the serum of all chronically infected animals, a substance(s) developed which inhibited phagocytosis of P. aeruginosa by normal cat alveolar macrophages. Phagocytosis was measured by incubating macrophage monolayers (5 X 10(5) alveolar macrophages) for 20 min in the presence of 3H-labeled bacteria and 5% serum from control or infected animals. Inhibitory activity developed 4 to 16 weeks after initial infection, and inhibition of phagocytosis of P. aeruginosa in the presence of infected cat serum ranged from 30 to 79%. After inhibitory activity developed, it persisted throughout the remainder of the experiment in each animal. The activity was specific for P. aeruginosa of the infecting serotype and did not affect phagocytosis of gram-positive organisms. Inhibitory activity was unchanged by heating serum at 56 degrees C for 30 min. We have previously described a P. aeruginosa-specific, heat-stable, phagocytosis-inhibitory activity in the serum of patients with cystic fibrosis. Since inhibitory activity also develops in cats with chronic P. aeruginosa pulmonary infection, such activity may not be a primary intrinsic abnormality in patients with cystic fibrosis. The animal model described here offers a system for following the development of and for characterization of the P. aeruginosa-specific phagocytosis-inhibitory activity.