Macrophage colony-stimulating factor and the enhanced migration of monocytes are essential in primary but not secondary host defenses to Listeria organisms.

Nonimmune mice infected with Listeria monocytogenes exhibited elevated expression of macrophage colony-stimulating factor (M-CSF) mRNA and the enhanced migration of Mac-1 antigen-positive bone marrow-derived mononuclear phagocytes (BMMP) to their livers. Treatment with monoclonal anti-M-CSF antibody diminished the traffic of BMMP and promoted the replication of listeriae. Immune animals infected with listeriae expressed significantly lower levels of M-CSF mRNA than did nonimmune animals. Moreover, listerial infections did not elicit the migration of BMMP to the livers of immune mice, nor did anti-M-CSF affect the capacity of immune animals to respond to infection. Adoptive immunization experiments suggest that T lymphocytes can mediate protective immunity to listeriae in the absence of M-CSF and migrating BMMP. These findings indicate that M-CSF and the enhanced migration of BMMP are critical factors in primary but not secondary host defenses to listerial infections.