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J. Exp. Med.,
Volume 188, Number 8, October 19, 1998 1541-1546
-dependent Clearance of Influenza A Virus
and Protection from Consolidating Pneumonitis in Nitric
Oxide Synthase 2-deficient Mice
By


From the * Host Defense Laboratory, Viral Engineering and Cytokines Group, Division of
Immunology and Cell Biology, The John Curtin School of Medical Research, The Australian National
University, Canberra, ACT 2601, Australia; and the Viral infection often activates the interferon (IFN)-
Beatrice and Samuel A. Seaver Laboratory,
Department of Medicine, Cornell University Medical College, New York 10021
-inducible gene, nitric oxide synthase 2 (NOS2). Expression of NOS2 can limit viral growth but may also suppress the immune system and damage tissue. This study assessed each of these effects in genetically deficient NOS2
/
mice after infection with influenza A, a virus against which IFN-
has no known activity. At
inocula sufficient to cause consolidating pneumonitis and death in wild-type control mice,
NOS2
/
hosts survived with little histopathologic evidence of pneumonitis. Moreover, they
cleared influenza A virus from their lungs by an IFN-
-dependent mechanism that was not evident in wild-type mice. Even when the IFN-
-mediated antiviral activity was blocked in NOS2
/
mice with anti-IFN-
mAb, such mice failed to succumb to disease. Further evidence that this protection was independent of viral load was provided by treating NOS2+/+
mice with the NOS inhibitor, N
-methyl-L-arginine (L-NMA). L-NMA prevented mortality
without affecting viral growth. Thus, host NOS2 seems to contribute more significantly to the
development of influenza pneumonitis in mice than the cytopathic effects of viral replication.
Although NOS2 mediates some antiviral effects of IFN-
, during influenza infection it can
suppress another IFN-
-dependent antiviral mechanism. This mechanism was observed only
in the complete absence of NOS2 activity and appeared sufficient to control influenza A virus
growth in the absence of changes in cytotoxic T lymphocyte activity.
;
virus infection;
influenza A;
cytotoxic T
lymphocyte
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