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From the * Institute of Experimental Immunology, University Hospital, CH-8091 Zürich,
Switzerland; Listeria monocytogenes is widely used as a model to study immune responses against intracellular
bacteria. It has been shown that neutrophils and macrophages play an important role to restrict bacterial replication in the early phase of primary infection in mice, and that the cytokines interferon-
Department of Internal Medicine, University Hospital, CH-8091 Zürich,
Switzerland; § Department of Pathology, University Hospital, CH-8091 Zürich, Switzerland;
Department of Molecular Genetics, Research Institute of Molecular Pharmacology, D-12207 Berlin,
Germany; and ¶ Ontario Cancer Institute, Princess Margaret Hospital, Toronto, Ontario, M4X1K9,
Canada
(IFN-
) and tumor necrosis factor-
(TNF-
) are essential for protection. However, the involved signaling pathways and effector mechanisms are still poorly understood. This
study investigated mouse strains deficient for the IFN-dependent transcription factors interferon consensus sequence binding protein (ICSBP), interferon regulatory factor (IRF)1 or 2 for
their capacity to eliminate Listeria in vivo and in vitro and for production of inducible reactive
nitrogen intermediates (RNI) or reactive oxygen intermediates (ROI) in macrophages.
ICSBP
/
and to a lesser degree also IRF2
/
mice were highly susceptible to Listeria infection. This correlated with impaired elimination of Listeria from infected peritoneal macrophage
(PEM) cultures stimulated with IFN-
in vitro; in addition these cultures showed reduced and
delayed oxidative burst upon IFN-
stimulation, whereas nitric oxide production was normal. In contrast, mice deficient for IRF1 were not able to produce nitric oxide, but they efficiently
controlled Listeria in vivo and in vitro. These results indicate that (a) the ICSBP/IRF2 complex is essential for IFN-
-mediated protection against Listeria and that (b) ROI together with additional still unknown effector mechanisms may be responsible for the anti-Listeria activity of
macrophages, whereas IRF1-induced RNI are not limiting.
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