Pathophysiological Aspects of Ocular Toxoplasmosis: Host-parasite Interactions

An alternative method to establish an early acute ocular toxoplasmosis model for experimental tests

PURPOSE

To provide a simple alternative acute ocular toxoplasmosis model with great reproducibility for experimental tests that demand monitoring of the ocular lesion.

METHODS

ME49-wt and ME49-GFP tachyzoites from cell culture were used to infect male C57BL6 mice by intraperitoneal injection. B1 expression by real-time polymerase chain reaction (qPCR) assay was used to detect the presence of T. gondii in ocular tissue at the beginning of the infection. Fluorescence microscopy and histopathology analysis were carried out to assess the evolution of the acute infection up to 20 days in both eyes of infected mice.

RESULTS

All mice infected with the 104 tachyzoites showed B1 expression in the retina of both eyes, in the RPE (retinal pigment epithelium), and choroid structures, after 5 days of infection. Tachyzoites of the ME49-GFP strain were easily detected by fluorescence microscopy in the retina tissue of mice after 5 days post-infection. After 20 days, mice inflammatory cell infiltrates and a disorganized morphology of the retinal laminar architecture were observed.

CONCLUSION

Infection of C57BL6 mice via intraperitoneal with 104 tachyzoites of the ME49-GFP strain from cell culture is a suitable model for acute ocular toxoplasmosis. This model has great reproducibility in establishing the ocular lesion since day 5 post-infection. This model can be suitable for experimental tests of chemotherapy and the investigation of the role of the immune response on the development of uveitis.

The Decreased Treg Cells Number Associated with Retinal Lesion Size in Ocular Toxoplasmosis

Introduction

The imbalance of the immune response is an important factor contributing to the incidence of ocular toxoplasmosis (OT). Regulatory T cells (Treg) play a key role in maintaining the balance between Th1 and Th17 immune responses, while interleukin-27 (IL-27) levels are related to the differentiation of Th17 cells. This study analyzes the differences in the number of Treg cells and the level of IL-27 between OT patients and seropositive individuals without ocular lesions and its correlation with retinal lesion size.

Methods

This analytic observational study, conducted for 8 months, involved 11 OT patients and 10 seropositive individuals without ocular lesions. All subjects underwent a comprehensive ophthalmological examination. Retinal lesions were documented by fundus photographs and the size was measured using Digimizer 4.2.2.0 software. Isolation of peripheral blood mononuclear cells (PBMC) was performed to measure the number of Treg cells using flow cytometry and interleukin-27 levels were assessed using the Sandwich enzyme-linked immunosorbent assay (ELISA) technique. Data were analyzed with SPSS.

Result

The number of Treg cells in the OT group (47.16 ± 15.66%) was lower than in the seropositive group without the ocular lesions (62.86 ± 17.08%) (p = 0.029). The serum IL-27 levels in the OT group were not significantly different from the seropositive group without the ocular lesions (p = 0.360). The number of Treg cells was significantly related to retinal lesion size (p = 0.043), with a correlation coefficient of -0.648, indicating a strong and inverse correlation. There was no significant correlation between serum IL-27 levels and retinal lesion size (p = 0.556).

Conclusion

Ocular toxoplasmosis patients have a low number of Treg cells that are inversely related to the retinal lesion size. The size of the retinal lesion increases as the number of Treg cells decreases.

Ocular Toxoplasmosis

INTRODUCTION

Ocular toxoplasmosis is the leading cause of posterior uveitis worldwide, affecting individuals acrossdifferent age groups. The key to reducing vision loss includes prompt diagnosis and treatment. However, despite the prevalence of ocular toxoplasmosis, there has been little consensus regarding its pathophysiology,clinical features, diagnosis, and especially management.

METHODS

The data sources were literature reviews, including Pub Med and Medline databases. Search terms included toxoplasmosis, retinitis, vasculitis, vitritis, uveitis alone or in combination with, serum, aqueous, vitreous eye, ocular and review.

RESULTS

In this review paper, we have sought to provide an overview of the pathophysiology, epidemiology, and clinical features of the disease, both based on current literature and our own clinical experience. We have also discussed the use of serology, ocular fluid, and ophthalmic investigations that could further facilitate the diagnosis of ocular toxoplasmosis.Different management strategies have been reported worldwide, including newer approaches such as local therapy.

CONCLUSION

A better understanding of critical aspects of ocular toxoplasmosis will hopefully lead to reduced morbidity, including blindness associated with this condition.

Association Between Ocular Trauma and Activation of Ocular Toxoplasmosis

PURPOSE

To evaluate the association between ocular trauma and activation of ocular toxoplasmosis.

METHODS

Retrospective review of 686 patients with ocular toxoplasmosis and its association with trauma to the eye or the head within 1 week of activation.

RESULTS

Ten patients with a history of trauma and activation of ocular toxoplasmosis were detected (10/686; 1.45%). Nine patients showed a primary focus of retinitis without a previous scar and one patient had a recurrent form of ocular toxoplasmosis. From these 10 patients, Toxoplasma IgG was positive in eight of them. The median age of the patients was 35.8 years-old (range 17 to 65).

CONCLUSIONS

These cases suggest that trauma can be associated with activation of retinal bradyzoite cysts in ocular toxoplasmosis.

Optical Coherence Tomography Angiography Findings in Ocular Toxoplasmosis with Multiple Recurrences

Ocular toxoplasmosis is the most common cause of posterior uveitis that is caused by Toxoplasma gondii infection. Humans can be infected congenitally or postnatally. The typical lesion of ocular toxoplasmosis is focal necrotizing retinitis with overlying vitritis, which lead to hyperpigmented retinochoroidal scar at resolution of lesion. Macula involvement can cause substantial visual impairment. The high incidence of disease reactivation may lead to greater risk of vision loss. Optical coherence tomography angiography (OCTA) is a non-invasive imaging method to visualize the vascular and density perfusion of the retina and choroid, which cannot be obtained by conventional Optical Coherence Tomography (OCT). In this case report, we present two cases of active ocular toxoplasmosis with multiple recurrences to study pathological changes in retinal and choroidal microvasculature. The findings reveal the involvement of all of the retinal layers in the choroid, with distinct changes in the deep retinal layer.