A dichotomous role for nitric oxide during acute Toxoplasma gondii infection in mice - PubMed (original) (raw)

A dichotomous role for nitric oxide during acute Toxoplasma gondii infection in mice

I A Khan et al. Proc Natl Acad Sci U S A. 1997.

Abstract

Production of nitric oxide by macrophages is believed to be an important microbicidal mechanism for a variety of intracellular pathogens, including Toxoplasma gondii. Mice with a targeted disruption of the inducible nitric oxide synthase gene (iNOS) were infected orally with T. gondii tissue cysts. Time to death was prolonged compared with parental controls. Histologic analysis of tissue from infected mice showed scattered small foci of inflammation with parasites in various tissues of iNOS-/- mice, whereas tissue from the parental C57BL/6 mice had more extensive tissue inflammation with few visible parasites. In particular, extensive ulceration and necrosis of distal small intestine and fatty degeneration of the liver was seen in the parental mice at day 7 postinfection, as compared with the iNOS-/- mice where these tissues appeared normal. Serum interferon gamma and tumor necrosis factor alpha levels postinfection were equally elevated in both mouse strains. Treatment of the parental mice with a NO synthase inhibitor, aminoguanidine, prevented early death in these mice as well as the hepatic degeneration and small bowel necrosis seen in acutely infected control parentals. These findings indicate that NO production during acute infection with T. gondii can kill intracellular parasites but can be detrimental, even lethal, to the host.

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Figures

Figure 1

Figure 1

Survival of iNOS−/− mice from oral T. gondii challenge. iNOS−/− and parental mice (n = 8/group) were orally infected with different number of cysts containing bradyzoites of T. gondii and mortality monitored. This study was performed three times with similar findings. Data presented are representative of one experiment.

Figure 2

Figure 2

Cytokine mRNA expression after T. gondii infection in iNOS−/− and parental mice. Mice were uninfected (−) or infected orally (+) with 50 cysts and on day 7 p.i. splenocytes from three mice were harvested and pooled, and mRNA expression for IFNγ and IL-10 was assayed by reverse transcriptase–PCR. The differences in the transcriptional level for both the genes are expressed relative to those mice treated with saline (level designated as 1). The cDNA concentration examined at each point was standardized to the hypoxanthine phosphoribosyltransferase mRNA level (not shown).

Figure 3

Figure 3

Photomicrographs of mouse tissues 7 days p.i. with T. gondii, processed as specified in Materials and Methods. Bars equal 30 μM. (A) Liver of C57BL/6 parental mouse showing an inflammatory nodule surrounded by hepatocytes with marked fatty degeneration. (B) Liver of iNOS−/− mouse showing acute inflammatory nodule among largely preserved hepatocytes. (C) Liver of sham-treated C57BL/6 parental mouse with changes similar to the untreated parental mouse. (D) Liver of aminoguanidine-treated parental mouse with inflammation but preservation of hepatocyte morphology. (E) Brain of parental mouse with acute inflammation and necrosis. (F) Brain of iNOS−/− mouse, with acute inflammation. Arrow indicates T. gondii tachyzoites.

Figure 4

Figure 4

Photomicrographs of mouse distal ileum 7 days p.i. with T. gondii. (A and B) Parental C57BL/6 mouse showing acute necrosis of small bowel villi with acute inflammatory infiltration and ulceration. (A) Bar equals 100 μM. (B) Bar equals 200 μM. (C) Parental mouse treated with aminoguanidine showing preservation of small bowel epithelium. Bar equals 100 μM. (D) iNOS−/− mouse with normal small bowel epithelium. Bar equals 75 μM.

Figure 5

Figure 5

Levels of parasite DNA in the organs of iNOS−/− and parental mice infected with T. gondii. Mice (n = 3/group) were infected orally with 50 cysts of T. gondii. DNA was prepared from the brain and liver of mice 7 days p.i. A slot blot analysis was probed with _T. gondii_-specific B1 sequence. The scanned auto radiogram was quantitated by NIH Image that used DNA from a known number of extracellular tachyzoites as control. Bars represent the average number of parasites detected in each tissue.

Figure 6

Figure 6

Levels of iNOS message in the intestine and liver of C57BL/6 mice infected with T. gondii. Mice were infected orally with cysts. On day 0, 4, and 7 p.i. the liver and distal ileum were isolated and stored at −70°C. The pooled tissues from three mice at each time point were homogenized, and mRNA expression for iNOS was assayed by reverse transcription–PCR. The transcriptional level is expressed relative to uninfected mice (designated as 1). The cDNA concentration examined at each point was standardized to the hypoxanthine phosphoribosyltransferase mRNA level (not shown).

Figure 7

Figure 7

Effect of aminoguanidine treatment on the susceptibility of mice infected with T. gondii. Parental mice (n = 6/group) were infected with 50 cysts and treated daily with 100 mg/kg body weight of aminoguanidine. Control mice were infected and administered saline. The experiment was performed twice with similar findings. The data presented is representative of one experiment.

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