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: Effect of Interleukin-12 in Experimental
Visceral Leishmaniasis in Interferon-
Gene-disrupted Mice
By
From the Department of Medicine, Cornell University Medical College, New York 10021
Despite permitting uncontrolled intracellular visceral infection for 8 wk, interferon-
(IFN-
)
gene knockout (GKO) mice infected with Leishmania donovani proceeded to reduce liver parasite burdens by 50% by week 12. This late-developing IFN-
-independent antileishmanial mechanism appeared to be dependent largely on endogenous tumor necrosis factor-
(TNF-
):
L. donovani infection induced TNF-
mRNA expression in parasitized GKO livers and neutralization of TNF-
reversed control at week 12. 7 d of treatment of infected GKO mice with
interleukin-12 (IL-12) readily induced leishmanicidal activity and also partially restored the
near-absent tissue granulomatous response, observations that for the first time expand the antimicrobial repertoire of IL-12 to include IFN-
-independent effects. The action of IL-12
against L. donovani was TNF-
dependent and required the activity of inducible nitric oxide
synthase. These results point to the presence of an IFN-
-independent antimicrobial mechanism, mediated by TNF-
, which remains quiescent until activated late in the course of experimental visceral leishmaniasis. However, as judged by the effect of exogenous IL-12 this quiescent mechanism can readily be induced to rapidly yield enhanced intracellular antimicrobial
activity.
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