CELLULAR RESISTANCE TO INFECTION

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Abstract
The mouse was found to be natively susceptible to Listeria monocytogenes. Its susceptibility was attributed to the capacity of the organism to survive and multiply in host macrophages. During the first 3 days of primary infection the bacterial populations of spleen and liver were found to increase at a constant rate. On the 4th day of infection the host became hypersensitive to Listeria antigens and bacterial inactivation commenced. Convalescent mice were resistant to challenge, but no protective factor could be found in their serum. When challenged in vitro, the macrophages of convalescent mice were found to resist infection with Listeria monocytogenes, Listeria-resistant cells appeared during the course of infection at a time which corresponded with the development of the antibacterial mechanism in the spleen. They persisted for as long as the antibacterial mechanism remained intact in this organ. This period of absolute resistance to Listeria lasted about 3 weeks. Thereafter, the host remained hypersensitive but unable to inactivate a challenge inoculum. However, an accelerated response to reinfection persisted. This was thought to depend on the generation of a new population of resistant cells by mitotic activity in specifically sensitized macrophage precursors.