August 2001
Volume 42, Issue 9
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Immunology and Microbiology  |   August 2001
Involvement of Apoptosis and Interferon-γ in Murine Toxoplasmosis
Author Affiliations
  • De Fen Shen
    From the Section of Immunopathology, Laboratory of Immunology, National Eye Institute, National Institutes of Health, Bethesda, Maryland.
  • Dawn M. Matteson
    From the Section of Immunopathology, Laboratory of Immunology, National Eye Institute, National Institutes of Health, Bethesda, Maryland.
  • Nadine Tuaillon
    From the Section of Immunopathology, Laboratory of Immunology, National Eye Institute, National Institutes of Health, Bethesda, Maryland.
  • Brandon K. Suedekum
    From the Section of Immunopathology, Laboratory of Immunology, National Eye Institute, National Institutes of Health, Bethesda, Maryland.
  • Ronald R. Buggage
    From the Section of Immunopathology, Laboratory of Immunology, National Eye Institute, National Institutes of Health, Bethesda, Maryland.
  • Chi-Chao Chan
    From the Section of Immunopathology, Laboratory of Immunology, National Eye Institute, National Institutes of Health, Bethesda, Maryland.
Investigative Ophthalmology & Visual Science August 2001, Vol.42, 2031-2036. doi:https://doi.org/
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      De Fen Shen, Dawn M. Matteson, Nadine Tuaillon, Brandon K. Suedekum, Ronald R. Buggage, Chi-Chao Chan; Involvement of Apoptosis and Interferon-γ in Murine Toxoplasmosis. Invest. Ophthalmol. Vis. Sci. 2001;42(9):2031-2036. doi: https://doi.org/.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

purpose. A murine toxoplasmosis model has been developed that results in central nervous system (CNS) and ocular inflammation characterized by encephalitis with numerous brain tissue cysts and milder inflammation with rare tissue cysts in the eye after 4 weeks of Toxoplasma gondii infection. In this model IFNγ and inducible nitric oxide (iNO) are protective against T. gondii infection. In this study, the role of apoptosis in the pathogenesis of toxoplasmosis was investigated.

methods. C57BL/6 (wild-type mice), B6MRL/lpr, and B6MRL/gld (defective Fas or FasL expression, respectively) mice were infected intraperitoneally with 20 to 30 tissue cysts of the ME-49 strain of T. gondii. Mice were killed at days 0, 14, or 28 after infection. The eyes and brains were harvested for histologic, immunohistochemical, and molecular studies. Analysis included immunostaining for Fas, FasL, Bcl-2, and Bax; in situ apoptosis detection (TUNEL assay); RT-PCR amplification for IFNγ; and measurement of ocular nitrite levels. The control mice were naïve mice of each strain that received no inoculation or injection.

results. Wild-type mice appeared to constitutively express apoptotic molecules at higher levels in the eye than in the brain. Consequently, during T. gondii infection, apoptosis was greater in the eyes than in the brain. Untreated naïve lpr and gld mice showed no expression of Fas and FasL, respectively. After infection, a slightly higher number of tissue cysts (lpr, 11.8 ± 2.4; gld, 10.3 ± 3.4) were found in the brains of the mutants than in the control animals (8.8 ± 2.9). However, no significant differences between the number of apoptotic cells, inflammatory scores, or number of tissue cysts were noted in the eyes. IFNγ mRNA in control mice was detected at day 28 after infection, whereas in both mutants, mRNA production occurred earlier, at day 14. Ocular nitrite levels were higher in lpr and gld mice than in wild-type mice.

conclusions. No significant difference in the degree of ocular inflammation and apoptosis was detected between the wild-type and Fas or FasL mutant mice. However, there was an earlier and subjectively greater expression of IFNγ in the brain and eye and a higher level of nitrite in the ocular tissue of mutant strains than in the wild type. Multiple factors are likely to be involved in the pathogenesis of ocular toxoplasmosis.

Infection with Toxoplasma gondii, a protozoan parasite normally controlled by the host immune system, results in an asymptomatic chronic infection maintained by dormant tissue cysts. However, infection with T. gondii may cause significant disease in newborns and immunocompromised patients, in particular, in patients with AIDS. 1 2 3 Ocular toxoplasmosis is believed to be the most common infectious disease involving the retina of immunocompetent individuals. 4 5 Although most ocular toxoplasmosis is thought to be congenital, 6 ocular involvement in cases of acquired infection appears to be more common than heretofore thought. 7 8  
Recently, a few experimental models of acquired ocular toxoplasmosis have been developed in mice. The mice are inoculated either systemically with bradyzoites 9 10 11 or intracamerally with tachyzoites. 12 In C57BL/6 mice infected intraperitoneally with the ME-49 strain of T. gondii, progressive meningoencephalitis and uveitis 9 13 develop 2 weeks after inoculation. Four weeks after inoculation, numerous tissue cysts and severe encephalitis with necrosis can be found in the brain. In contrast, only rare tissue cysts surrounded by little or no inflammation are observed in the eye. In this model, interferon (IFN)-γ and inducible nitric oxide (iNO) have been demonstrated to have a direct role in prevention and protection against toxoplasmic infection. 9 14 15 16 17  
Apoptosis, a naturally occurring mechanism of cell death involved in a large range of physiological and pathologic events, is characterized by a set of specific alterations in cell morphology. 18 19 This finely regulated mechanism of cell death has been shown to be of critical importance in immune response, including responses against parasitic infection. 20 21 B6MRL/lpr (lpr denoting lymphoproliferation) and B6MRL/gld (gld denoting generalized lymphoproliferative disease) mice, well-characterized animal models of autoimmune diseases, are loss-of-function mutants of the Fas (CD95) and FasL (CD95 ligand) genes, respectively. 22 Hu et al. 23 reported greater intraocular inflammation in lpr and gld mice than in wild-type control C57BL/6 (B6) mice inoculated intraocularly with T. gondii. 23 They concluded that Fas–FasL interaction associated with apoptosis was involved in the pathogenesis of acquired ocular toxoplasmosis in mice. The present study examines the role of apoptosis in toxoplasmosis in a murine model that more closely resembles acquired toxoplasmosis in humans. 
Materials and Methods
Animals
Female C57BL/6 (B6), lpr, and gld mice were obtained from the Division of Cancer Treatment, National Cancer Institute (Frederick, MD). The lpr and gld mice were backcrossed onto the C57BL/6J background 10 and 11 times, respectively. The mice were housed under specific pathogen-free conditions, given water and chow ad libitum, and used at 6 to 8 weeks of age. Treatment of the animals conformed to the ARVO Statement on the Use of Animals in Ophthalmic and Vision Research. 
T. gondii Infection
The ME-49 strain of T. gondii was used in the study. Freshly prepared tissue cysts were obtained from brains of B6 mice inoculated at least 1 month earlier. Mice of three different strains were infected by intraperitoneal injection of 20 to 30 tissue cysts in PBS (a total volume of 0.1 ml) per animal. 9 Two uninoculated naïve mice of each strain without inoculation or PBS injection were killed at baseline as control animals. 
Evaluation of Toxoplasmic Infection in Mice
Three repeated experiments were performed. In each experiment, there were 30 B6, 15 lpr, and 15 gld mice. At time points of 0, 14, and 28 days after the infection, 5 lpr, 5 gld, and 5 to 10 B6 mice were killed. One eye and one half sagittally sectioned brain were submitted for routine histology. The other eye and half brain were either embedded in optimal cutting temperature (OCT) compound and sectioned frozen for immunohistochemistry or microdissection or were frozen for RT-PCR or measurement of ocular nitrite levels. 
The freshly collected eyes and brain samples for histology were prefixed for 1 hour in phosphate-buffered glutaraldehyde (4%), postfixed in phosphate-buffered formaldehyde (10%) overnight, dehydrated, and embedded in paraffin. Sections were stained with hematoxylin and eosin and periodic acid-Schiff base. Incidence and severity of ocular and brain inflammatory lesions were graded on a scale of 0.0 to 4.0 in half-point increments, according to a semiquantitative system described previously. 9 24 The total number of Toxoplasma tissue cysts was counted in each section. 
Immunohistochemical Technique
Snap-frozen ocular and brain tissues were embedded in OCT and stored at −70°C. Four-micrometer serial sections were stained using the avidin-biotin-peroxidase complex technique. 25 26 The primary antibodies were polyclonal rabbit antibodies against mouse Fas, FasL (Santa Cruz Biotechnology, Inc., Santa Cruz, CA), Bcl-2, or Bax (PharMingen, San Diego, CA) or control immunoglobulin. The secondary antibody was biotin-conjugated goat anti-rabbit IgG (Vector Laboratories, Burlingame, CA). The substrate was avidin-biotin-peroxidase complex and the chromogen was diaminobenzide. 
In Situ Labeling of Cell Nuclear DNA Fragmentation by the TUNEL Technique
In situ detection of apoptotic cells was conducted by using a kit (TACS Blue Label Detection kit; Trevigen, Inc., Gaithersburg, MD) according to the manufacturer’s protocol. This protocol was based on the original TUNEL technique to identify cleaved double-stranded DNA ends in a particular cell. 27 Briefly, the paraffin-embedded slides were deparaffinized and rehydrated. The slides were then treated with proteinase K to increase tissue permeability. Two percent H2O2 was added to quench the endogenous peroxides. Tissue was in situ labeled with a dNTP mix and TdT in the presence of MnCl2 and incubated at 37°C. The reaction was terminated by the stop buffer. Streptavidin-horseradish peroxidase conjugates were added to the tissue. The positive signals were visualized by the blue label. The slide was then counterstained with red counterstain C. TUNEL-positive cells were counted on each section (whole eye or half brain). Four sections were averaged for each sample. 
Microdissection
Microdissection was performed as previously described. 28 Briefly, frozen ocular sections were stained with hematoxylin and eosin. Inflammatory and retinal cells in a focal lesion were selected by visualization under a light microscope and microdissected with a 30-gauge needle. The selected histologic area in the eye was gently scraped until the selected cells became detached from the tissue section. Under microscopic visualization the loose cells were carefully picked up by the needle and immediately placed in a denaturing solution (4 M guanidinium thiocyanate, 25 mM sodium citrate, 0.5% sarcosyl, 0.1 M β-mercaptoethanol). RNA was extracted by phenol-chloroform. After digestion with DNase, total RNA was used for reverse transcription–polymerase chain reaction (RT-PCR) amplification. 
Because the lesions in the brain were much larger and severe than in the eye, it was not necessary to perform microdissection on brain sections. Total RNA was extracted from frozen fresh brain tissues. 
IFNγ mRNA Detection by RT-PCR and Nested PCR
Complementary DNA was synthesized using a kit (Superscript II RNase H Reverse Transcriptase system; Life Technologies, Grand Island, NY) with random primers (Promega, Madison, WI). The nested PCR for microdissected ocular samples was initiated with 5 μl cDNA. A 10× buffer (GeneAmp; Perkin Elmer, Hayward, CA) was used at a final concentration of 1.5 mM MgCl2 together with 4.0 nanomoles of each dNTP, 3 picomoles of each primer, and 1.0 U polymerase (AmpliTaq Gold; Perkin Elmer, Hayward, CA), at a final volume of 25 μl. The second PCR round was initiated with 1 μl of the first-round PCR product. A 32P-labeled sense primer was used for the second PCR round. PCR conditions were 35 cycles of 94°C for 45 seconds, 55°C for 60 seconds, and 72°C for 120 seconds for the first PCR round and 40 cycles of 94°C for 45 seconds, 58°C for 60 seconds, and 72°C for 120 seconds for the second round. Hot start at 94°C for 9 minutes was used for both rounds. Primers for the first round were IFNγ sense, 5′-AAC GCT ACA CAC TGC ATC T-3′, and antisense, 5′-GAC TTC AAA GAG TCT GAC G-3′. Primers for the second round were sense, 5′-CTT CCT CAT GGC TGT TTC-3′, and antisense, 5′-CCA GTT CCT CCA GAT ATC-3′. The expected size of the final PCR products was 236 bp. 
For brain samples, 0.5 μg cDNA was mixed with a 32P-labeled primer set of β-actin or a 32P-labeled second-round primer set of IFNγ and conditioner. After polyacrylamide gel electrophoresis, PCR products were scanned using a phosphorimager-fluorimager (Storm 860; Molecular Dynamics, Sunnyvale, CA). The radioactivity of each PCR product was analyzed (ImageQuant, ver. 1.2; Molecular Dynamics). The β-actin signal of each sample showed the same level of radioactivity. The highest value for IFNγ among all samples was chosen and calibrated as 100% mRNA expression. Primers for β-actin were sense, 5′-CCT GTG GCA TCC ATG AAA CT-3′, and antisense, 5′-GTG CTA GGA GCC AGA GCA CT-3′. The expected size of the PCR product was 160 bp. 
Nitrite Measurement
For nitrite measurement, frozen eyes were ground in 1 ml PBS. The homogenate was centrifuged, and the supernatant was collected. Nitrite was assayed by Griess colorimetric reaction. 29 Briefly, 50 μl supernatant was diluted with distilled water to 500μ l and mixed with 500 μl Griess reagent, containing 1.0% sulfanilamide and 50 μl 0.1% N-(1-naphthyl) ethylenediamine dihydrochloride (Sigma Chemical Co., St. Louis, MO) in 2.5% phosphoric acid, at room temperature. The absorbency was read after 10 minutes in a spectrophotometer (model DU 640; Beckman Coulter, Palo Alto, CA) at 550 nm in reference to a standard nitrite quantitative curve. 
Statistical Analysis
Histologic grades of inflammation, tissue cyst numbers, TUNEL-positive cells, and nitrite levels among the various groups were presented as the mean ± SE. Differences between groups were compared by computer, using analysis of variance (ANOVA; StatView; SAS, Inc., Cary, NC). P < 0.05 were considered statistically significant. 
Results
Cerebral and Ocular Inflammation
Three repeated experiments yielded similar results. Uninoculated, naïve wild-type, lpr, and gld mice showed no inflammation. After inoculation, all three murine strains showed inflammation in the brains and eyes characteristic of toxoplasmic infection, as reported previously. 9 By day 14 after inoculation there was mild to moderate encephalitis with focal necrosis, cerebral vasculitis, meningitis, and focal mild ocular inflammation, including iridocyclitis, vitreitis, retinal vasculitis, retinal folds, and choroiditis. Twenty-eight days after infection, the disease became worse, with moderate to severe encephalitis and meningitis and mild to moderate uveitis, retinitis, chorioretinal scarring, and RPE alterations (Fig. 1) . Histologic grades in the eyes at 28 days were B6, 1.25 ± 0.25; lpr, 1.95 ± 0.74; and gld, 2.0 ± 0.54. No significant differences in the histologic grading, however, were found between the wild-type and the two mutant strains (P > 0.4). 
Numerous Toxoplasma tissue cysts were observed in the brain but rarely in the eye. Although not statistically significant, higher numbers of tissue cysts were counted in the brains of both mutants than in control animals: 11.8 ± 2.4 in lpr, 10.3 ± 3.4 in gld, and 8.8 ± 2.9 in B6 mice. Ocular tissue cysts were extremely rare (B6, only one tissue cyst in 2 of 90 mice in three experiments; lpr, one tissue cyst in 1 of 45 mice in three experiments; gld, no tissue cyst, but tachyzoites in 1 of 45 mice in three experiments), and no differences were noted among the three strains. 
Apoptosis in the Brains and Eyes
Expression of Fas and FasL was shown in the eyes and to a lesser degree in the brain of uninfected wild-type B6 mice. The expression was slightly enhanced 28 days after inoculation with T. gondii (Fig. 2) . There was no Fas expression in lpr mice and no FasL in gld mice. During toxoplasmic infection, FasL expression in lpr mice and Fas expression in gld were enhanced (Fig. 2) . No differences were found in the expression of Bcl-2 and Bax in both tissues of the three strains (data not shown). DNA fragmentation was observed among the inflammatory cells by TUNEL in B6 mice and both mutants (Fig. 2) , but no significant differences in apoptosis among T. gondii infected B6, lpr (without Fas), and gld (without FasL) mice was observed (P > 0.1). 
Ocular and Cerebral IFNγ mRNAs
Ocular IFNγ mRNA was detected by nested PCR in the microdissected cells from B6 mice only at day 28 after inoculation with T. gondii (Fig. 3) . In contrast, IFNγ mRNA was detected in the eyes of lpr and gld mice at day 14 after inoculation and remained increased at 28 day after infection in these mutant mice. 
In the brains, total IFNγ mRNA was detected at days 14 and 28 in all mice. The IFNγ message, however, was significantly stronger in both mutant strains than in the B6 wild type at each time point during the course of infection (Fig. 3) . The differences were even greater at the early stage of T. gondii infection. 
Ocular Nitrite Production
Production of ocular nitrite was measured in all three strains. In normal eyes of B6, lpr, and gld mice the nitrite content was limited. The increase of nitrite production in infected eyes was statistically significant in all three strains (P < 0.02; Table 1 ). In addition, ocular nitrite levels were significantly higher in the two mutant mice than in the wild-type mice at day 14 (lpr versus B6, P < 0.01; gld versus B6, P < 0.02). Nitrite production was increased in all strains at day 28. However, at this stage the difference between the mutants and wild-type mice was no longer statistically significant (lpr versus B6, P = 0.19; gld versus B6, P = 0.39). 
Discussion
Systemic toxoplasmosis causes destructive inflammation that targets multiple organs, including the brain and eye. In our murine model more severe inflammatory disease develops and more parasites are contained in the central nervous system (CNS) than in the eye. 9 16 Although autoreactive inflammatory processes have been suggested to play a role in eyes infected by T. gondii, 30 apoptosis may also contribute to the pathogenesis of toxoplasmic infection. Fas–FasL interaction is important for maintaining lymphocyte homeostasis during immune responses by signaling for activation-induced cell death. Fas and FasL are expressed at high levels in normal eyes but at relatively lower levels in the brain. 31 32 Constitutive expression of Fas and FasL has been shown to be protective against ocular viral infection. 31 33  
Recently, Fas–FasL interaction has also been suggested to play a role in the pathogenesis of ocular toxoplasmosis in another murine model in which infection is induced by direct intracameral inoculation of T. gondii. 23 In that model, greater ocular inflammation and reduced apoptosis was found in the inoculated lpr and gld mutant strains, compared with the wild type. In contrast, our study did not show a significant difference in the degree of ocular inflammation and apoptosis among the three groups of mice, although a nonstatistical trend toward higher inflammatory scores was noted in the mutant strains. The discrepancy between these two models may result from different methods used to establish the T. gondii infection. We used intact eyes instead of the surgically traumatized eyes used in the other model. 23 Apoptosis induced by mechanisms other than Fas–FasL interaction, such as the proapoptotic effects of aqueous humor on inflammatory cell types, 34 may play different roles in the pathologic courses of the two systems. In an experimental autoimmune uveitis (EAU) model using gld and lpr mice immunized with a retinal antigen, data show that expression of Fas and FasL on the target tissue does not seem to affect ocular inflammatory induction in EAU. 35  
Although defects in the Fas–FasL system that normally mediates apoptosis have been shown to be an important factor in the lymphoproliferative disorders of lpr and gld mice, 36 the complex pathogenesis of autoimmune diseases cannot be fully explained by an alteration of one signaling pathway alone. 37 38 Similarly, in the present study parasitic disease in the mutant mice with a defective apoptotic system was not significantly greater than that in wild-type control animals. Furthermore, apoptosis in the eye and brain as measured by TUNEL assay did not show a statistical difference among the mutants and wild types. Therefore, additional mechanisms that contribute to disease development and progression are yet to be determined. 
Apoptosis is unlikely to be the only critical factor in the pathogenesis of toxoplasmic infection. IFNγ is a key cytokine in resistance to T. gondii infection. 14 In vivo studies have shown that resistance to either acute or chronic toxoplasmosis can be abrogated by treatment with anti-IFNγ antibody, 9 14 15 39 40 whereas recombinant IFNγ prevents infectious disease and mortality in murine toxoplasmosis. 41 42 43 IFNγ and TNFα are crucial elements in controlling parasite growth. 44 IFNγ is absolutely required for an efficient activation of macrophages, which are of critical importance in the host defense against toxoplasmosis. 45 46 In the present study, expression of IFNγ mRNA occurred earlier in the eyes and at higher level in the eyes and brain of both murine strains with defective apoptosis than in their wild-type control counterparts. In our model the high levels of IFNγ may have had a protective effect against T. gondii infection and may have abrogated the CNS and ocular inflammation. 
Another inflammatory mediator that plays an important role in toxoplasmic infection is iNO. 16 Inhibition of NO production leads to a concomitant increase in the number of infectious organisms and in the level of the inflammatory reaction in the eye. In the present study, ocular nitrite production was increased after T. gondii infection, particularly at 14 days in mutant mice. iNO production and Fas–FasL interactions have been shown to mediate apoptosis in ocular inflammation. 47 Therefore, high iNO in the infected mutant eyes may have contributed to protecting the mice against the parasitic infection. 
The results presented in this report suggest that the establishment of a symbiotic equilibrium between the Toxoplasma parasite and its host does not rely exclusively on Fas–FasL mediated apoptosis, but may also depend on the function of several inflammatory factors, including IFNγ and iNO. Apoptosis may have a dual role in protozoan infection, an early beneficial effect for the host by eliminating the parasite, and a later, detrimental effect on the host by inducing autoimmune or other tissue-destroying effects. Alteration of the host response by apoptosis is one factor that may allow the parasite to survive and sustain infection. In contrast, IFNγ and NO are critical effectors for the protective immune response to T. gondii infection. Early production of IFNγ and iNO in infected mice with defective apoptosis systems appears to hinder the development of severe toxoplasmosis. 
 
Figure 1.
 
Photomicrography showing ocular (top row) and CNS (bottom row) lesions (black arrows) and bradyzoites (white arrows) in the three murine strains infected with T. gondii for 1 month. In two mutant strains, slightly more intense inflammatory response developed, although the inflammatory scores among the three groups were not significantly different. (A, D) B6; (B, E) lpr; (C, F) gld. Periodic acid-Schiff base; magnification,× 400.
Figure 1.
 
Photomicrography showing ocular (top row) and CNS (bottom row) lesions (black arrows) and bradyzoites (white arrows) in the three murine strains infected with T. gondii for 1 month. In two mutant strains, slightly more intense inflammatory response developed, although the inflammatory scores among the three groups were not significantly different. (A, D) B6; (B, E) lpr; (C, F) gld. Periodic acid-Schiff base; magnification,× 400.
Figure 2.
 
Photomicrography showing ocular expression ( Image not available ) of Fas and FasL (top and middle rows) and apoptosis (bottom row) in the three murine strains 1 month after T. gondii inoculation. (AC) Fas immunohistochemistry for the three strains, with positive expression (purple-gray) for B6 and gld strains ( Image not available , positive staining area) and negative expression of Fas in the lpr strain. (DF) Negative expression of FasL in the gld strain. (GI) TUNEL assay for the three strains. Arrows: positive cells. (AF) Avidin-biotin-complex immunoperoxidase; (GI) TUNEL; magnification, ×400.
Figure 2.
 
Photomicrography showing ocular expression ( Image not available ) of Fas and FasL (top and middle rows) and apoptosis (bottom row) in the three murine strains 1 month after T. gondii inoculation. (AC) Fas immunohistochemistry for the three strains, with positive expression (purple-gray) for B6 and gld strains ( Image not available , positive staining area) and negative expression of Fas in the lpr strain. (DF) Negative expression of FasL in the gld strain. (GI) TUNEL assay for the three strains. Arrows: positive cells. (AF) Avidin-biotin-complex immunoperoxidase; (GI) TUNEL; magnification, ×400.
Figure 3.
 
RT-PCR showing ocular (top) and CNS (middle) expressions of IFNγ mRNA during T. gondii infection. IFNγ mRNA was expressed much earlier in the eyes and more intensely in the brains of the two mutants than in brains of the wild-type mice. Expression of the housekeeping gene β-actin (bottom) is shown. Ocular message was detected by nested PCR.
Figure 3.
 
RT-PCR showing ocular (top) and CNS (middle) expressions of IFNγ mRNA during T. gondii infection. IFNγ mRNA was expressed much earlier in the eyes and more intensely in the brains of the two mutants than in brains of the wild-type mice. Expression of the housekeeping gene β-actin (bottom) is shown. Ocular message was detected by nested PCR.
Table 1.
 
Nitrite Levels in Mice Eyes Infected with T. gondii
Table 1.
 
Nitrite Levels in Mice Eyes Infected with T. gondii
Strain Baseline Day after T. gondii Infection
0 14 28
B6 (wild type) 0.36 0.49 ± 0.03 0.70 ± 0.04 0.81 ± 0.01
lpr (Fas mutant) 0.43 0.48 ± 0.02 1.00 ± 0.04 (P < 0.01) 1.11 ± 0.20 (P = 0.19)
gld (FasL mutant) 0.40 0.40 ± 0.01 0.87 ± 0.07 (P < 0.02) 1.00 ± 0.23 (P = 0.39)
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Figure 1.
 
Photomicrography showing ocular (top row) and CNS (bottom row) lesions (black arrows) and bradyzoites (white arrows) in the three murine strains infected with T. gondii for 1 month. In two mutant strains, slightly more intense inflammatory response developed, although the inflammatory scores among the three groups were not significantly different. (A, D) B6; (B, E) lpr; (C, F) gld. Periodic acid-Schiff base; magnification,× 400.
Figure 1.
 
Photomicrography showing ocular (top row) and CNS (bottom row) lesions (black arrows) and bradyzoites (white arrows) in the three murine strains infected with T. gondii for 1 month. In two mutant strains, slightly more intense inflammatory response developed, although the inflammatory scores among the three groups were not significantly different. (A, D) B6; (B, E) lpr; (C, F) gld. Periodic acid-Schiff base; magnification,× 400.
Figure 2.
 
Photomicrography showing ocular expression ( Image not available ) of Fas and FasL (top and middle rows) and apoptosis (bottom row) in the three murine strains 1 month after T. gondii inoculation. (AC) Fas immunohistochemistry for the three strains, with positive expression (purple-gray) for B6 and gld strains ( Image not available , positive staining area) and negative expression of Fas in the lpr strain. (DF) Negative expression of FasL in the gld strain. (GI) TUNEL assay for the three strains. Arrows: positive cells. (AF) Avidin-biotin-complex immunoperoxidase; (GI) TUNEL; magnification, ×400.
Figure 2.
 
Photomicrography showing ocular expression ( Image not available ) of Fas and FasL (top and middle rows) and apoptosis (bottom row) in the three murine strains 1 month after T. gondii inoculation. (AC) Fas immunohistochemistry for the three strains, with positive expression (purple-gray) for B6 and gld strains ( Image not available , positive staining area) and negative expression of Fas in the lpr strain. (DF) Negative expression of FasL in the gld strain. (GI) TUNEL assay for the three strains. Arrows: positive cells. (AF) Avidin-biotin-complex immunoperoxidase; (GI) TUNEL; magnification, ×400.
Figure 3.
 
RT-PCR showing ocular (top) and CNS (middle) expressions of IFNγ mRNA during T. gondii infection. IFNγ mRNA was expressed much earlier in the eyes and more intensely in the brains of the two mutants than in brains of the wild-type mice. Expression of the housekeeping gene β-actin (bottom) is shown. Ocular message was detected by nested PCR.
Figure 3.
 
RT-PCR showing ocular (top) and CNS (middle) expressions of IFNγ mRNA during T. gondii infection. IFNγ mRNA was expressed much earlier in the eyes and more intensely in the brains of the two mutants than in brains of the wild-type mice. Expression of the housekeeping gene β-actin (bottom) is shown. Ocular message was detected by nested PCR.
Table 1.
 
Nitrite Levels in Mice Eyes Infected with T. gondii
Table 1.
 
Nitrite Levels in Mice Eyes Infected with T. gondii
Strain Baseline Day after T. gondii Infection
0 14 28
B6 (wild type) 0.36 0.49 ± 0.03 0.70 ± 0.04 0.81 ± 0.01
lpr (Fas mutant) 0.43 0.48 ± 0.02 1.00 ± 0.04 (P < 0.01) 1.11 ± 0.20 (P = 0.19)
gld (FasL mutant) 0.40 0.40 ± 0.01 0.87 ± 0.07 (P < 0.02) 1.00 ± 0.23 (P = 0.39)
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