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 t he enhanced migration of Mac-I antigen-positive bone marrow-derived mo nonuclear phagocytes (BMMP) to their livers. Treatment with monoclonal anti-M-CSF antibody diminished the traffic of BMMP and promoted the r eplication of listeriae. Immune animals infected with listeriae expres sed significantly lower levels of M-CSF mRNA than did nonimmune animal s. 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 exper iments suggest that T lymphocytes can mediate protective immunity to l isteriae in the absence of M-CSF and migrating BMMP. These findings in dicate that M-CSF and the enhanced migration of BMMP are critical fact ors in primary but not secondary host defenses to listerial infections .