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Infect Immun, August 1998, p. 3510-3518, Vol. 66, No. 8
Immunobiology Section,
Received 25 March 1998/Returned for modification 14 April
1998/Accepted 6 May 1998
High levels of nitric oxide (NO) are produced by inducible nitric
oxide synthase (iNOS) in response to activating signals from
Th1-associated cytokines and play an important role in cytotoxicity and
cytostasis against many pathogenic microorganisms. In addition to its
direct effector function, NO serves as a potent immunoregulatory factor. NO produced by gamma interferon-activated macrophages immobilizes and kills Schistosoma mansoni larvae, and
several studies have indicated a role for this pathway in protective
immunity against this parasite. The potential regulatory influence of
NO in immunity to S. mansoni is less well understood. In
this study, we have used iNOS-deficient mice to determine the role of
NO in mice vaccinated with irradiated cercariae of S. mansoni. We show by enzyme-linked immunosorbent assay and reverse
transcriptase PCR analysis that vaccinated iNOS-deficient mice develop
exacerbated type 1 cytokine responses in the lungs, the site where
resistance to infection is primarily manifested. In addition,
parasite-specific immunoglobulin G2a (IgG2a) and IgG2b antibody
responses were significantly increased in vaccinated iNOS-deficient
animals and total IgE antibody levels in serum were decreased relative
to those in wild-type controls. Surprisingly, since resistance in this
vaccine model is largely Th1 dependent and since Th1-related cellular
and humoral immune responses were found to be exacerbated in vaccinated
iNOS-deficient mice, vaccine-elicited protective immunity against
challenge infection was found to be reduced. These findings demonstrate
that iNOS plays a paradoxical role in immunity to S. mansoni, both in the effector mechanism of resistance and in the
down regulation of the type 1 cytokine response, which is ultimately
required for NO production.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Inducible Nitric Oxide Synthase-Deficient Mice
Develop Enhanced Type 1 Cytokine-Associated Cellular and Humoral
Immune Responses after Vaccination with Attenuated
Schistosoma mansoni Cercariae but Display Partially
Reduced Resistance
*
Corresponding author. Mailing address: National
Institutes of Health, Bldg. 4, Room 126, 9000 Rockville Pike, Bethesda,
MD 20892-0425. Phone: (301) 496-4758. Fax: (301) 402-0077. E-mail: tw12b{at}nih.gov.
Infect Immun, August 1998, p. 3510-3518, Vol. 66, No. 8
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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