MURINE LISTERIOSIS AS A MODEL OF ANTIMICROBIAL DEFENSE

Murine listeriosis was introduced 35 years ago as a model with which t o analyze mechanisms of antibacterial defense that are independent of antibodies. Listerio manocytogenes was shown to be an intramacrophage pathogen with capacity to induce the generation of a state of specific immunity in the form of DTH and a macrophage system with enhanced non -specific bactericidal activity The demonstration that anti-listeria i mmunity and DTH can be passively transferred with T cells was taken to indicate that the T cells responsible for DTH function upregulate the listericidal function of macrophages. This interpretation is contradi cted by recent research showing that CD8 T cells, rather than CD4 T ce lls, are responsible for mediating adoptive immunity. However, T-cell depletion studies show that primary infection can eventually be resolv ed in the absence of either CD8 or CD4 T cells. On the other hand, inf ection becomes lethal in the absence of neutrophils or NK cells. It is apparent. therefore, that the most important defense against primary listeriosis resides with the functions of neurophils and NK cells that are mobilized early in infection. Antigen-specific T cells function a t a later time to resolve infection more efficiently. It is apparent t hat T cells are much more important in defense against secondary infec tion.