NEUTROPHILS ARE INVOLVED IN ACUTE, NONSPECIFIC RESISTANCE TO LISTERIA-MONOCYTOGENES IN MICE

The importance of neutrophils in killing extracellular, pyogenic bacte ria has long been established. However, there is only indirect evidenc e for a role for neutrophils in resistance against intracellular organ isms. In this study, we directly demonstrate the involvement of neutro phils in defense against Listeria monocytogenes in normal C.B-17 immun ocompetent and C.B-17 SCID mice. Because of the lack of sterilizing T- cell immunity, SCID mice are unable to completely eliminate listeriae systemically and become chronically infected. Both immunocompetent and SCID mice treated with a specific neutrophil-depleting monoclonal ant ibody during the early stages of Listeria infection were rendered rema rkably sensitive to the organism, with a high level of mortality resul ting from enhanced bacterial growth. At a late stage of infection in S CID mice, however, administration of neutrophil-depleting antibody did not affect mortality. In spite of the neutrophil depletion, other par ameters of nonspecific immune function were normal. Macrophage infiltr ation to the site of infection and macrophage expression of major hist ocompatibility complex class II molecules were unaffected. Moreover, N K cell functions were normal as measured by infiltration to an infecti on site and gamma interferon production. These data demonstrate an imp ortant role for neutrophils in controlling the acute phase of Listeria infection, cooperating with, and yet independent of, macrophages and NK cells.