Alterations in the bactericidal ability of rabbit alveolar macrophages as a result of tumbling stress

Bacteriologic and electron microscopic studies support observations that the degradative phase of the phagocytic process in rabbit alveolar macrophages is altered by subjecting the animals to tumbling stress. Macrophages from control and stressed rabbits have similar ultrastructural features. In vitro incubation of macrophages from stressed animals with Pseudomonas aeruginosa showed that the process of bacterial ingestion was not impaired, nor were the numbers of bacteria ingested decreased as compared to control macrophages. However, the ability of macrophages from stressed animals to kill ingested bacteria was significantly decreased. Bacterial plate counts after 30 minutes incubation showed that approximately 70% of the ingested organisms had been killed by control macrophages, whereas there was practically no kill by macrophages from stressed animals even after 90 minutes. Electron microscopy demonstrated extensive degradation of Pseudomonas within phagocytic vacuoles of control macrophages. These changes consisted of cytoplasmic swelling, clumping of nuclear material and disruption of the bacterial cell wall. In contrast, bacterial degradation was not observed within macrophages from stressed animals at any of the intervals studied (up to 90 minutes after rotation). This form of stress thus appears to deprive the alveolar macrophages of the ability to destroy ingested microorganisms, a factor which may be important to the establishment of pulmonary infections.