Administration of small amounts of salmonella endotoxin (20 µg.) or of acetone-extracted BCG cells (100 µg.) increases the resistance of mice to infection with Myco. fortuitum as well as their ability to clear carbon particles from their blood stream. Whereas the increased resistance to infection persists for many weeks, the clearing power returns to a normal level within a few days.
When normal mice are infected with Myco. fortuitum, there occurs during the first phase of the infectious process a rise in clearing power for carbon particles followed by a fall during the terminal phase of the disease. The rise occurs more rapidly and is more pronounced in animals previously treated with salmonella endotoxin or with killed BCG cells. This acceleration and intensification of the phagocytic response to infection can be detected even in animals which exhibit a normal phagocytic index when tested several weeks after administration of endotoxin or of BCG.
Although increase in resistance to infection is correlated with activation of the so called reticulo-endothelial system, there is no evidence of any direct causal relationship between the two phenomena.