Roles of factor increasing monocytopoiesis (FIM) and macrophage activation in host resistance to Listeria monocytogenes.

The present contribution concerns two aspects of host resistance in overcoming an infection with Listeria monocytogenes. One of these aspects is the regulation of monocyte production by the factor increasing monocytopoiesis (FIM), a macrophage-derived factor. Listeria-resistant (C57BL/10 mice and Listeria-sensitive CBA mice produce and secrete similar amounts of FIM in response to an inflammation induced by soluble Listeria antigen. However, monocyte precursors in the bone marrow of Listeria-resistant mice react to an injection of serum containing FIM by increased monocyte production, whereas Listeria-sensitive mice are unable to react to this stimulus. The other aspect of host resistance to L. monocytogenes is the activation of macrophages leading to increased bactericidal activity. Macrophages of both mouse strains stimulated first with live BCG and then with PPD, killed ingested Listeria faster than resident peritoneal macrophages did. However, recombinant interferon-gamma, thought to be the most important macrophage-activating factor, did not induce increased listericidal activity in macrophages.