Genetically determined resistance to listeriosis is associated with increased accumulation of inflammatory neutrophils and macrophages which have enhanced listericidal activity.

The C57BL/6 and A/J inbred strains of mice differ markedly in their resistance to the facultative intracellular bacterium Listeria monocytogenes. One possible explanation for this genetically determined resistance is that phagocytes from Listeria-resistant strains of mice can kill L. monocytogenes more effectively than phagocytes from Listeria-susceptible strains of mice. We report here that inflammatory neutrophils and macrophages from Listeria-resistant mice (C57BL/6) exhibit a slight but significantly enhanced ability to kill L. monocytogenes in vitro as compared to inflammatory phagocytes from Listeria-susceptible mice (A/J). More importantly, however, Listeria-resistant mice recruited more inflammatory neutrophils and macrophages to the peritoneal cavity in response to i.p. injection of heat-killed Listeria than did Listeria-susceptible mice. These data suggest that genetically determined resistance to listeriosis is dependent on the enhanced inflammatory responsiveness of Listeria-resistant mice. Further support for this hypothesis was provided by experiments in which the passive transfer to A/J mice (C5-deficient) of plasma from C57BL/6 mice (C5-sufficient) enhanced the ability of the recipient A/J mice both to recruit inflammatory neutrophils to the peritoneal cavity in response to i.p. injection of heat-killed Listeria, and to clear L. monocytogenes from the spleen after a sublethal challenge of viable Listeria.