Subretinal fluid in eyes with active ocular toxoplasmosis observed using spectral domain optical coherence tomography

PURPOSE

To describe the clinical finding of subretinal fluid (SRF) in the posterior pole by spectral domain optical coherence tomography (SD-OCT) in eyes with active ocular toxoplasmosis (OT).

DESIGN

Retrospective case series.

PARTICIPANTS

Thirty-nine eyes from 38 patients with active OT [corrected]..

METHODS

Eyes with active OT which underwent SD-OCT were reviewed. SRFs in the posterior pole were further analyzed.

MAIN OUTCOME MEASURES

Presence of SRF; its accompanying features, e.g. retinal necrosis, cystoid macular edema (CME), choroidal neovascularization (CNV); and longitudinal changes of SRF, including maximum height and total volume before and after treatment.

RESULTS

SRF presented in 45.5% (or 15/33) of eyes with typical active OT and in 51.3% (or 20/39) of eyes with active OT. The mean maximum height and total volume of SRF were 161.0 (range: 23-478) µm and 0.47 (range: 0.005-4.12) mm3, respectively. For 12 eyes with SRF related to active retinal necrosis, SRF was observed with complete absorption after conventional anti-toxoplasmosis treatment. The mean duration for observation of SRF clearance was 33.8 (range: 7-84) days. The mean rate of SRF clearance was 0.0128 (range: 0.0002-0.0665) mm3/day.

CONCLUSIONS

SRF (i.e., serous retinal detachment) is a common feature in patients with active OT when SD-OCT is performed. The majority of SRF was associated with retinal necrosis and reacted well to conventional therapy, regardless of total fluid volume. However, SRF accompanying with CME or CNV responded less favorably or remained refractory to conventional or combined intravitreal treatment, even when the SRF was small in size.

Interleukin-6 gene polymorphism (-174 G/C) is associated with toxoplasmic retinochoroiditis

PURPOSE

Experimental data have demonstrated a relevant role for IL-6 in the modulation of acute ocular toxoplasmosis. Therefore, we aim to investigate the possible association between the IL-6 gene polymorphism at position -174 and toxoplasmic retinochoroiditis (TR) in humans.

METHODS

Ninety-seven patients with diagnosed TR were recruited from the Uveitis Section, Federal University of Minas Gerais. For comparison, 83 healthy blood donors with positive serology for toxoplasmosis and without retinal signs of previous TR were included in the study. Genomic DNA was obtained from oral swabs of individuals and amplified using polymerase chain reaction (PCR) with specific primers flanking the locus -174 of IL-6 (-174G/C). PCR products were submitted to restriction endonuclease digestion and analysed by polyacrylamide gel electrophoresis to distinguish allele G and C of the IL-6 gene, allowing the detection of the polymorphism and determination of genotypes.

RESULTS

There was a significant difference in the genotype (χ(2) = 12.9, p = 0.001) and allele (χ(2) = 6.62, p = 0.01) distribution between TR patients and control subjects. In a subgroup analysis, there was no significant difference in genotypes and allele frequencies regarding TR recurrence.

CONCLUSIONS

This study suggests that the genotypes related with a lower production of IL-6 may be associated with the occurrence of TR.

IFN-gamma-regulated Toxoplasma gondii distribution and load in the murine eye

PURPOSE

To establish a mouse model of ocular toxoplasmosis in both wild type (WT) and immunocompromised hosts and to clarify the effects of interferon (IFN)-gamma on the infectivity of Toxoplasma gondii in various parts of the eye.

METHODS

Susceptible WT C57BL/6, resistant WT BALB/c, and IFN-gamma knockout (GKO) mice were infected with cysts of T. gondii perorally. The tissues were harvested for molecular and histopathologic studies. Analysis included a quantitative competitive polymerase chain reaction (QC-PCR) assay and reverse transcription (RT)-PCR for IFN-gamma and stage conversion markers. All animals underwent ophthalmic examinations including fluorescein angiography (FA).

RESULTS

In WT C57BL/6 mice, T. gondii was detected in tissue in the following order: brain, retina, choroid, sclera, and optic nerve (ON). The highest T. gondii load was observed in the posterior retina, and was much greater than that in WT BALB/c mice. In GKO mice, disseminated infection was evident, and the T. gondii load was highest in the choroid and ON. IFN-gamma mRNA expression in WT C57BL/6 mice was higher than that in WT BALB/c mice after infection. Tachyzoites existed in GKO mice, whereas bradyzoites existed in WT C57BL/6 mice. FA showed dye leakage from the retinal capillaries of GKO mice.

CONCLUSIONS

The T. gondii load in the retina in the susceptible WT strain continued to increase, unlike in the resistant WT strain. IFN-gamma was shown to regulate the T. gondii load and interconversion in the eye. A toxoplasmic vasculitis model was established with GKO mice and assay systems with QC-PCR and FA.

Involvement of apoptosis and interferon-gamma in murine toxoplasmosis

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 IFN gamma 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 IFN gamma; 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. IFN gamma 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 IFN gamma 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.

Inhibition of nitric oxide production exacerbates chronic ocular toxoplasmosis

There is considerable controversy as to the roles of parasite proliferation and the inflammatory response in destruction of the retina during Toxoplasma gondii infection. A murine model was used to investigate the role of nitric oxide in pathogenesis of chronic ocular toxoplasmosis. Increased quantities of messenger RNA (mRNA) transcripts for iNOS were detected in the eyes of chronically infected C57BL/6 mice compared with noninfected control mice. Inhibition of nitric oxide (NO) by the addition of Lomega-nitro-L-arginine methyl ester (L-NAME) to the drinking water of infected mice between weeks 4-6 of infection, exacerbated ocular inflammation. The amount of inflammation was assessed semiquantitatively in histological sections of the eye. Eyes from L-NAME treated mice showed a significant increase in inflammation of the retina (P = 0.02), choroid (P = 0.03), and vitreous (P = 0.02) compared with control mice. These results demonstrate a protective role for NO in the control of chronic, ocular toxoplasmosis.

Analysis of immunoregulatory cytokines in ocular fluid samples from patients with uveitis

PURPOSE

To investigate the T-helper cell cytokine profiles in two well-defined clinical uveitis entities caused by an infectious mechanism.

METHODS

Cytokines (interleukin [IL]-2, IL-4, IL-6, IL-10, and interferon [IFN]-gamma) were measured in ocular fluid samples obtained from patients with herpes simplex- or varicella-zoster virus-induced acute retinal necrosis (ARN; n = 17) and toxoplasma chorioretinitis (n = 27) using enzyme-linked immunosorbent assay techniques. The data were compared with data for 51 control samples taken during cataract surgery (n = 10), vitrectomy in diabetic retinopathy (n = 10), eye bank eyes (n = 10) and with samples from patients with "autoimmune" uveitis (n = 21).

RESULTS

Interleukin-6 was detected in 44 of 51 control samples and 43 of 44 eyes of patients with uveitis. The highest levels in the control samples were detected in 9 of 10 vitreous samples from patients with diabetic retinopathy (mean, 648 pg/ml). In 8 of 10 samples taken from patients during cataract surgery and in 7 of 10 eye bank eyes the amount of IL-6 was significantly lower (mean, 10 pg/ml and 136 pg/ml, respectively). Interleukin-6 levels in patients with ARN (mean, 1436 pg/ml) were significantly higher than in those with toxoplasma chorioretinitis (mean, 272 pg/ml). Interleukin-2 was detected in one of the samples from patients with toxoplasma chorioretinitis (1105 pg/ml) and in three samples from the control subjects suffering from Fuchs' heterochromic anterior uveitis (mean, 752 pg/ml). No IL-4 (<2 pg/ml) was detected either in patient or control samples. Interferon-gamma could be detected in 7 of 17 ARN patients (range, 277-3483 pg/ml), in 13 of 27 samples from patients with toxoplasma chorioretinitis (range, 12-250 pg/ml), and in 1 of 21 of the samples from control subjects with uveitis (31 pg/ml) but was absent in nonuveitic control samples. Interleukin-10 was detected in 10 of 17 ARN patients (range, 29-3927 pg/ml), in 13 of 27 samples from patients with toxoplasma chorioretinitis (range, 4-67 pg/ml), and in only 3 of 51 control samples (6 pg/ml, 16 pg/ml, and 20 pg/ml).

CONCLUSIONS

Various immunoregulatory cytokines (IL-6, IL-10, and IFN-gamma) were detected in ocular fluid samples from patients with uveitis. A separate role for either a T-helper type 1 or T-helper type 2 response in the pathogenesis of clinical uveitis could not be proven.

Protective role of nitric oxide in ocular toxoplasmosis

AIMS

To evaluate the role of nitric oxide (NO) in ocular involvement during systemic toxoplasmosis.

METHODS

C57B1/6 mice were infected with Toxoplasma gondii strain ME49. The synthesis of NO was inhibited by an intraperitoneal injection of aminoguanidine every 8 hours, starting on the day of infection. Control infected mice received phosphate buffered saline vehicle alone. After 14 days, the ocular lesions were evaluated by histopathological examination. The expression of NO synthase induced in the spleen by toxoplasma infection was evaluated by immunostaining. The production of NO by the spleen cells of infected mice was measured by the colorimetric assay of Griess in the supernatant of cultures stimulated with toxoplasma antigen or concanavalin A.

RESULTS

The inhibition of NO production in T gondii infected mice resulted in a marked increase in the symptoms of ocular inflammation. We observed a strong induction of NO synthase expression in the spleen of infected animals. In culture, the spleen cells from these mice produced high levels of NO in response to T gondii antigens. This elevation of NO synthesis was suppressed in the presence of aminoguanidine.

CONCLUSION

This study indicates that NO plays a crucial role in the protection against T gondii infection as reflected by the severity of the ocular involvement.

Paradoxical effect of clindamycin in experimental, acute toxoplasmosis in cats

Cats were experimentally inoculated parenterally with the ME49 strain of Toxoplasma gondii to characterize the efficacies of two different dosages of orally administered clindamycin hydrochloride in the treatment of ocular toxoplasmosis. Concentrations of clindamycin hydrochloride at levels previously suggested to be inhibitory to T. gondii replication in vitro were achieved in the serum and aqueous humor but not in the cerebrospinal fluid. Antibiotic therapy, initiated 7 days after inoculation, resulted in no significant difference in the morphometric severity of ocular posterior segment lesions compared with that in the control groups. Treatment appeared to blunt T. gondii-specific immunoglobulin M production but had no significant effect on immunoglobulin G titers. Paradoxically, clindamycin administration was associated with increased morbidity and mortality from hepatitis and interstitial pneumonia, which are characteristic of generalized toxoplasmosis. Serum tumor necrosis factor alpha activity was detected at moderate levels in all groups of cats and correlated with the severity of clinical disease. The results of the study suggest that clindamycin, when administered at this specific time interval following inoculation, does not ameliorate ocular lesions and has a detrimental effect on the clinical course of acute, experimental toxoplasmosis in cats. The factors responsible for and the relevance of this detrimental effect to naturally occurring toxoplasmosis in humans and pet cats were not clear from the study but may relate to an antibiotic-associated decrease in the antitoxoplasmic activity of phagocytic cells responsible for the control of T. gondii.