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J. Exp. Med.,
Volume 186, Number 9, November 3, 1997 1495-1502
Activation of Human Blood Mononuclear
Cells In Vitro and In Vivo for Nitric Oxide Synthase (NOS)
Type 2 mRNA and Protein Expression: Possible
Relationship of Induced NOS2 to the Anti-Hepatitis C
Effects of IFN-
In Vivo
By



From the * Division of Gastroenterology and Although researchers have noted high level activation of rodent mononuclear phagocytes for
nitric oxide (NO) synthase type 2 (S2) expression and NO production with a variety of agents
such as interferon (IFN)
Division of Hematology-Oncology, Department of
Medicine, Veterans Affairs and Duke University Medical Centers, Durham, North Carolina 27705
and endotoxin, it has been difficult to demonstrate activation of human mononuclear phagocytes. The purpose of this study was to determine if IFN-
serves as
an activator in vitro and in vivo in humans. Treatment of normal monocytes or mononuclear
cells in vitro with IFN-
caused a dose-dependent increase in monocyte NOS2 activity and
NO production, and increased expression of NOS2 protein and mRNA expression. To determine if in vivo administration of IFN-
also modulated NOS2, we studied blood cells from
patients with hepatitis C before and after IFN-
therapy. Untreated patients with chronic hepatitis C virus infection had levels of NOS activity and NOS2 antigen in freshly isolated mononuclear cells similar to those of healthy subjects, and they expressed minimal or no NOS2
mRNA. However, IFN-
treatment of patients with hepatitis C infection was associated with
a significant elevation in mononuclear cell NOS activity, NOS2 antigen content, and NOS2
mRNA content. IFN-
-treated patients had significant decreases in levels of serum alanine
aminotransferase and plasma hepatitis C mRNA. The degree of IFN-
-enhanced mononuclear cell NOS2 antigen content correlated significantly with the degree of reduction in serum
alanine aminotransferase levels. Thus, IFN-
treatment of cells in vitro or administration of
IFN-
to hepatitis C patients in vivo increases expression of mononuclear cell NOS2 mRNA
expression, NOS activity, NOS2 antigen expression, and NO production. Since NO has been
reported to have antiviral activity for a variety of viruses, we speculate that induced NO production may be related to the antiviral action(s) of IFN-
in hepatitis C infection.
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