Human Ocular Toxoplasmosis Research Articles

Human Ocular Toxoplasmosis in Romania: History, Epidemiology, and Public Health: A Narrative Review.

Toxoplasmosis, caused by the protozoan parasite Toxoplasma gondii (T. gondii), presents a significant global health concern, particularly for immunocompromised individuals and congenitally infected newborns. Despite its widespread prevalence, there are limited data on T. gondii seroprevalence and ocular toxoplasmosis in Romania. This review aims to summarize the research accomplished on the prevalence and epidemiology of human ocular toxoplasmosis in Romania. Ocular toxoplasmosis, a leading cause of infectious posterior uveitis worldwide, involves complex interactions between host immune responses and parasite factors. Clinically, it presents as focal necrotizing retinitis, characterized by active focal retinal lesions with adjacent chorioretinal scarring, often accompanied by vitreous inflammation and anterior chamber reactions. Diagnosis relies on clinical examination supported by fundus photography, optical coherence tomography (OCT), and serological assays. The authors followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards, conducting a literature review on PubMed, Google Scholar, and Scopus. Our focus was on ocular toxoplasmosis in Romania, and we used keywords and specific MeSH terms. Finally, 17 articles met all the criteria, as summarized in the PRISMA diagram. This study underscores the need for improved diagnostic methods, increased research efforts, and comprehensive public health education to mitigate the burden of toxoplasmosis and ocular toxoplasmosis in Romania.

Local and systemic gene expression levels of IL-10, IL-17 and TGF-β in active ocular toxoplasmosis in humans

BackgroundTo compare mRNA expression of interleukin 10 (IL-10), interleukin 17 (IL-17) and Transforming Growth Factor-β (TGF-β) in aqueous humor (AH) and peripheral blood mononuclear cells (PBMCs) in human ocular toxoplasmosis (OT) and controls. MethodRNA isolation, cDNA synthesis and real-time polymerase chain reaction were performed on AH sediments and PBMCs of 16 patients with active OT and 21 controls at the Khatam-al-Anbia Eye Hospital, Iran. For comparison, Mann Whitney U test was used at a discrimination level of p < 0.05. Pearson and Spearman rank correlation test were applied for correlation with clinical parameters. ResultsThe expression for IL-10 and IL-17 in the AH was 3.7- and 88.0-fold higher in OT than in controls (P = 0.04 and P = 0.03, respectively) whereas that of TGF-β was 7.7-fold lower (P < 0.001). The expression levels for these cytokines in PBMC followed a similar pattern (IL-10 13.8-fold down-regulated (P = 0.001), IL-17 with 1.9-fold insignificantly upregulated (p = 0.43), TGF-β 452.8-fold down-regulated (P = 0.002). Compared to PBMC, IL-10 coding mRNA was 1876-fold higher in the almost cell-free AH in OT (39.2-fold in controls), IL-17 coding mRNA was 9.4-fold higher (17.7-fold down-regulated in controls), and that coding for TGF-β 207-fold higher in OT (7x105-fold in controls). The expression for IL-10, IL-17 and TGF-β in AH thus followed an opposite pattern compared to that in PBMC. ConclusionOT induces a highly-specific local immunoregulatory process as evidenced by an intraocular up-regulation of IL-10 and down-regulation of TGF-β mRNA. This could indicate an attempt to prevent unnecessary tissue damage which is in line with a moderate local mRNA up-regulation for IL-17 which seems sufficient to control parasite proliferation. That this regulation is opposite to that in PBMC may be linked to intraocular immune deviation in the course of disease.

Murine Model of Primary Acquired Ocular Toxoplasmosis: Fluorescein Angiography and Multiplex Immune Mediator Profiles in the Aqueous Humor.

PurposeTo establish a murine model of primary acquired ocular toxoplasmosis (OT) and to investigate the immune mediator profiles in the aqueous humor (AH).MethodsC57BL/6 mice were perorally infected with Toxoplasma gondii. The ocular fundus was observed, and fluorescein angiography (FA) was performed. The AH, cerebrospinal fluid (CSF), and serum were collected before infection and at 28 days post-infection (dpi); the immune mediator levels in these samples were analyzed using multiplex bead assay.ResultsFundus imaging revealed soft retinochoroidal lesions at 14 dpi; many of these lesions became harder by 28 dpi. FA abnormalities, such as leakage from retinal vessels and dilation and tortuosity of the retinal veins, were observed at 14 dpi. Nearly all these abnormalities resolved spontaneously at 28 dpi. In the AH, interferon-γ, interleukin (IL)-1α, IL-1β, IL-6, IL-10, IL-12(p40), IL-12(p70), CCL2/MCP-1, CCL3/MIP-1α, CCL4/MIP-1β, CCL5/RANTES, and CXCL1/KC levels increased after infection. All these molecules except IL-1α, IL-4, and IL-13 showed almost the same postinfection patterns in the CSF as they did in the AH. The tumor necrosis factor α, IL-4, and IL-5 levels in the AH and CSF of the T. gondii–infected mice were lower than those in the serum. The postinfection IL-1α, IL-6, CCL2/MCP-1, CCL4/MIP-1β, and granulocyte colony-stimulating factor levels in the AH were significantly higher than those in the CSF and serum.ConclusionsA murine model of primary acquired OT induced via the natural infection route was established. This OT model allows detailed ophthalmologic, histopathologic, and immunologic evaluations of human OT. Investigation of AH immune modulators provides new insight into OT immunopathogenesis.

Treatment Strategy in Human Ocular Toxoplasmosis: Why Antibiotics Have Failed.

Background: There is currently no clear evidence of the effectiveness of antibiotic therapy in acute ocular toxoplasmosis (OT), but its effect as a secondary prophylaxis is undisputed. The majority of uveitis specialists advocate treatment. This meta-analytic review aims to critically analyze determinants of treatment success and to update current treatment strategies for OT in order to explain this discrepancy. Methods: A systematic literature search was performed in NCBI/PubMed, Clinical Trials, Google Scholar and ScienceDirect to retrieve pro- and retrospective studies using the key terms “ocular toxoplasmosis” or “retinochoroiditis” and “immunocompetent” and “treatment” or “therapy” and “human.” Of these, larger case series and prospective clinical studies and cross references identified from meta-analyses were selected by a manual search, and primary and secondary outcome parameters were extracted. Results: Ten case series and clinical trials reported success parameters for treatment outcomes, and four additional for recurrence prophylaxis. Five treatment studies were randomized clinical trials, three comparative and two noncomparative case series. Though several outcome parameters were reported, five of them defined time to healing, four visual gain and one lesion size as primary and secondary outcome parameters, recurrence rate as a secondary outcome parameter was reported once. No conclusive evidence was found for an antibiotic treatment effect. Four prophylaxis studies addressed the prevention of recurrences after treatment. The primary outcome in all studies was the effect of treatment and prophylaxis on recurrences, and all four found a significant effect on the risk of and time to recurrences. Conclusions: Antibiotic treatment of OT aims at controlling parasite proliferation. The absence of an effect on visual acuity and time to healing is thus not surprising. The fact that time to and number of recurrences respond to recurrence of prophylaxis proves the antibiotic effect on parasite activity.

Serotyping, host genes and cytokines response in human ocular toxoplasmosis

In human ocular toxoplasmosis, serotype is related with greater severity. We analyzed Toxoplasma GRA6 serotype in 23 patients with ocular toxoplasmosis (13 confirmed, two co-infections- and eight unconfirmed cases) and 20 individuals chronically infected with Toxoplasma but without ocular involvement. In patients with ocular toxoplasmosis, we also studied host gene polymorphisms related to immune response (IL-1β; IL-1α; IL-10; IFN-γ; TNF-α, IL-12), IL-17R, TLR-9, and P2RX7. Additionally, eight patients were studied for the production of TNFα, IL1-β, IFN−γ and IL-10 by their peripheral leukocytes after ex vivo stimulation with soluble Toxoplasma antigens. There were no differences in the distribution of serotypes (GRA6-I versus GRA6 non-I) between infected individuals with- or without ocular involvement. Seropositivity for GRA6-I was associated with higher number of retinal lesions and higher levels of IL-1β. Two polymorphisms were associated with specific clinical manifestations of ocular toxoplasmosis: IL-10 -819 C/T with bilateral lesions and IL-12 + 169,774 A/C with synechia. Higher levels of IL-10 were found in patients with the allele G/G at the polymorphic region IL-10 -1082. People with a GRA6 I serotype and possessing the allele G/G at the polymorphic region TNFα-857 suffered from an increased number of retinal lesions. We found a positive association between host cytokine genes polymorphisms and GRA6 serotypes correlated with specific clinical manifestations and immune response in ocular toxoplasmosis.

Pathogenesis of ocular toxoplasmosis.

Ocular toxoplasmosis is a retinitis -almost always accompanied by vitritis and choroiditis- caused by intraocular infection with Toxoplasma gondii. Depending on retinal location, this condition may cause substantial vision impairment. T. gondii is an obligate intracellular protozoan parasite, with both sexual and asexual life cycles, and infection is typically contracted orally by consuming encysted bradyzoites in undercooked meat, or oocysts on unwashed garden produce or in contaminated water. Presently available anti-parasitic drugs cannot eliminate T. gondii from the body. In vitro studies using T. gondii tachyzoites, and human retinal cells and tissue have provided important insights into the pathogenesis of ocular toxoplasmosis. T. gondii may cross the vascular endothelium to access human retina by at least three routes: in leukocyte taxis; as a transmigrating tachyzoite; and after infecting endothelial cells. The parasite is capable of navigating the human neuroretina, gaining access to a range of cell populations. Retinal Müller glial cells are preferred initial host cells. T. gondii infection of the retinal pigment epithelial cells alters the secretion of growth factors and induces proliferation of adjacent uninfected epithelial cells. This increases susceptibility of the cells to parasite infection, and may be the basis of the characteristic hyperpigmented toxoplasmic retinal lesion. Infected epithelial cells also generate a vigorous immunologic response, and influence the activity of leukocytes that infiltrate the retina. A range of T. gondii genotypes are associated with human ocular toxoplasmosis, and individual immunogenetics -including polymorphisms in genes encoding innate immune receptors, human leukocyte antigens and cytokines- impacts the clinical manifestations. Research into basic pathogenic mechanisms of ocular toxoplasmosis highlights the importance of prevention and suggests new biological drug targets for established disease.

Model Systems for Studying Mechanisms of Ocular Toxoplasmosis.

The most common human disease caused by infection with Toxoplasma gondii is ocular toxoplasmosis, which typically is manifest as recurrent attacks of necrotizing retinal inflammation with subsequent scarring. The multilayered retina contains specialized cell populations, including endothelial cells, epithelial cells, neurons and supporting cells, all of which may be involved in this condition. In vitro investigations of basic mechanisms operating in human ocular toxoplasmosis use cellular and molecular methods that are common to the study of many pathological processes, and the novel aspect of this research is the use of human retinal cell subsets. Most in vivo research on ocular toxoplasmosis is conducted in the laboratory mouse. Experimental models involve local or systemic inoculation of parasites to induce acute disease, or sequential systemic and local parasite inoculations to trigger recurrent disease. We present methods for in vitro and in vivo studies of ocular toxoplasmosis, including dissection of the human eye, and culture and infection of differentiated cell populations from the retina, as well as induction of mouse ocular toxoplasmosis by intraocular, or sequential systemic and intraocular, inoculations, and imaging of toxoplasmic retinal lesions.

Neutrophil Activities in Human Ocular Toxoplasmosis: An In Vitro Study With Human Cells.

Retinal damage in ocular toxoplasmosis reflects Toxoplasma gondii-induced cell lysis and reactive inflammation. Human retinal histopathology demonstrates the presence of neutrophils, but activities of this leukocyte subset are unstudied. We conducted in vitro experiments to evaluate roles for neutrophils as retinal taxis for T. gondii and as contributors to the inflammation. Human neutrophils were isolated from peripheral blood. Migration to disease-relevant chemokines was evaluated in transwells, seeded with human retinal endothelial cells for some assays, using neutrophils infected with GT-1 strain T. gondii tachyzoites. Neutrophils were cocultured with T. gondii-infected ARPE-19 and primary human retinal pigment epithelial cells, and production of reactive oxygen species (ROS) was estimated by dihydroethidium reaction. Proteins produced by T. gondii-infected ARPE-19 cells were profiled by immunoarray, and candidate neutrophil-activating proteins were targeted with specific blocking antibody in coculture assays. Infection with T. gondii arrested neutrophil migration across retinal endothelium regardless of the presence of CXCL8. Migration to CXCL1, CXCL2, and CXCL8 also was significantly inhibited in infected neutrophils. Neutrophils generated more ROS when cocultured with infected versus uninfected ARPE-19 cells and three of four primary retinal pigment epithelial cell isolates. Infected ARPE-19 cells augmented the synthesis of 12 neutrophil-activating proteins also expressed by primary retinal pigment epithelial cells. Antibody blockade of granulocyte-macrophage colony-stimulating factor, interleukin-6 (IL-6) and IL-18 significantly reduced ROS production by neutrophils cocultured with T. gondii-infected ARPE-19 cells. Our findings support involvement of neutrophils in retinal inflammation, but not parasite transport, in the setting of ocular toxoplasmosis.

Epidemiological Investigation of Toxoplasma gondii Infections in Commercial Sheep Flock in an Endemic Area for Ocular Toxoplasmosis in Southern Brazil.

Toxoplasma gondii is a widely distributed parasite and of great importance to human and animal health. The objective of this study was to assess the prevalence of T. gondii antibodies and risk factors associated with the infection in sheep in the Northwest region of the State of Rio Grande do Sul, Brazil; this region has a very high rate of human ocular toxoplasmosis. Ovine sera were tested by the modified agglutination test (cut-off 1:25). T. gondii antibodies were detected in 70.2% (224 of 319). According to the logistic regression, the most significant factors associated were age and cat access to food stock facility. Preventive measures are discussed to reduce the risk of transmission of this zoonosis.

Müller cell activation and photoreceptor depletion in a mice model of congenital ocular toxoplasmosis

Müller glial cells are critically involved in retinal inflammatory processes. Here, we investigate the activation of Müller cells in a model of congenital ocular toxoplasmosis (OT). Four weeks after infection, retinal sections were studied immunohistochemically using the markers glial fibrillary acidic protein (GFAP) and vimentin. Müller cells showed strong up-regulation of both markers, as well as a deteriorated morphology in all infected retinas. Moreover, cell density and color intensity of the outer nuclear layer (ONL) of photoreceptors were decreased. Our results indicate that the severe retinal damage and loss of vision observed in human OT may be not only directly caused by infection but rather mediated by infection induced reactive gliosis.

Determinants of immunodiagnostic success in human ocular toxoplasmosis

Ocular toxoplasmosis is a local manifestation of systemic infection in which Toxoplasma spreads into the eye, affecting mainly the posterior segment of the eye. Reactivation of the initial retinal condition presumably results from the rupture of quiescent parasitic cysts lying adjacent to pre-existing scars and may secondarily involve the choroid (leading to retinochoroiditis). Although the molecular mechanisms underlying host-parasite interaction are largely unknown, toxoplasmic retinochoroiditis usually remains a local event, and does not necessarily evoke a detectable systemic immune response. Local immunotolerance mechanisms may likewise confound attempts to confirm the clinical diagnosis by serology. Aqueous humour may be analysed for the presence of parasite DNA or of specific antibodies, but the DNA burden therein is low, and a more definite confirmation would require risky puncturing of the vitreous. Laboratory confirmation of the diagnosis is also frustrated by marked individual differences in the time elapsing between the onset of clinical symptoms and the activation of specific antibody production, resulting in a high proportion of false negative results. Whether a delay in the onset of local specific antibody production reflects immunotolerance in cases of congenital - but not obviously in those of acquired - infection remains an open question, but it could account for a relatively low confirmation rate in laboratory tests for local antibody production. Against this background, current diagnostic strategies need to be re-evaluated with a view to future improvements.

Aqueous humor and serum immunoblotting for immunoglobulin types G, A, M, and E in cases of human ocular toxoplasmosis.

The purpose of this study was to compare the local and systemic Toxoplasma-specific humoral immune responses in individuals with ocular toxoplasmosis (OT). To this end, paired aqueous humor and serum samples from 46 individuals with active OT and from 30 individuals without inflammatory eye disease (controls) were analyzed by immunoblotting for anti-Toxoplasma immunoglobulin G (IgG), IgA, IgM, and IgE directed against 20- to 120-kDa antigens. The presence in the aqueous humor of a unique band, or of at least three bands that were at least three times more intense in aqueous humor than in serum, was taken as evidence of local antibody production. IgG bands were detected in 98% of the aqueous humor samples, while IgA bands were detected in 76%, IgM bands were detected in 8%, and IgE bands were not detected in any. Evidence of local production of specific antibodies was found in 32 cases (70%) (IgG in 23 [50%]; IgA in 16 [35%]). In 10 instances (22%), routine laboratory tests were not indicative of OT. In 14 cases (30%), no local antibody production was detected by immunoblotting; 3 of these cases yielded evidence of local antibody production according to the Goldmann-Witmer coefficient. Local antibody production was revealed for 7 of the 30 controls (23%). Hence, the sensitivity of immunoblotting for IgG and IgA is 70%, and the specificity is 77%. We conclude that immunoblotting for local specific IgG and IgA supports the clinical diagnosis of OT in 70% of cases. In 22% of these, the diagnosis is not confirmed by other laboratory tests. Hence, immunoblotting increases the sensitivity of routine laboratory tests and should be considered for samples that register negative by such tests.

Evidence for a compartmentalized B cell response as characterized by IgG epitope specificity in human ocular toxoplasmosis.

Infectious agents in the eye induce both a local and a systemic humoral immune response. Previously, differences in Ag recognition were observed between systemic and ocular derived IgG of patients with ocular toxoplasmosis. This finding implied a nonrandom distribution of IgG-producing B cells in the inflamed eye. In the present study, we compared the intraocular and systemic B cell responses of patients with ocular toxoplasmosis to a single Toxoplasma gondii Ag. Two series of C-terminally deleted recombinant T. gondii GRA-2 proteins were constructed to delineate IgG B cell epitopes of paired ocular and serum samples. Differences in epitope region recognition between the ocular and systemic compartment were detected in 9 of 13 patients. The difference in distribution of GRA-2 epitopes between paired samples is indicative of a local GRA-2 specific B cell population functionally different from the systemic GRA-2-specific B cell population. Our results suggest a selective activation of a subset of B cells locally in nonlymphoid tissue.

Early aqueous humor analysis in patients with human ocular toxoplasmosis.

To evaluate the diagnostic sensitivity of a panel of laboratory tests for ocular toxoplasmosis performed at the time of presentation, paired samples of aqueous humor and serum were collected from 49 consecutive episodes of ocular toxoplasmosis with a clinical course of less than 3 weeks. Total immunoglobulin G (IgG) and Toxoplasma gondii-specific IgG, IgM, and IgA were quantified by enzyme-linked immunosorbent assay. The avidity of T. gondii-specific IgG was determined, and DNA extracted from aqueous humor was amplified for detection of a glycoprotein B gene sequence of T. gondii. The diagnosis was confirmed for 73% (36 of 49) of the patients; this rate rose to 79.5% if data from a later analysis of aqueous humor derived from five of the negative patients were included. The analysis of serum (detection of T. gondii-specific IgM and analysis of consecutive serum samples) alone did not contribute to the diagnosis. Calculation of local antibody production lacked diagnostic sensitivity when it was determined less than 3 weeks after the manifestation of clinical symptoms (28 of 49 patients [57%]), but this rose to 70% after an analysis of a second aqueous humor sample. The antibody avidity index attained diagnostic significance in only 8 of 43 instances (19%), and T. gondii DNA was amplified from no more than 6 of 39 (16%) aqueous humor samples. However, T. gondii-specific IgA was found within the aqueous humors of 11 of 43 patients (26%); measurement of the T. gondii-specific IgA level thus contributed substantially to the diagnostic sensitivity of the laboratory tests.

HTLV-I infection in the Middle East

To compare mRNA expression of interleukin 10 (IL-10), interleukin 17 (IL-17) and Transforming Growth Factor-β (TGF-β) in aqueous humor (AH) and peripheral blood mononuclear cells (PBMCs) in human ocular toxoplasmosis (OT) and controls.RNA isolation, cDNA synthesis and real-time polymerase chain reaction were performed on AH sediments and PBMCs of 16 patients with active OT and 21 controls at the Khatam-al-Anbia Eye Hospital, Iran. For comparison, Mann Whitney U test was used at a discrimination level of p < 0.05. Pearson and Spearman rank correlation test were applied for correlation with clinical parameters.The expression for IL-10 and IL-17 in the AH was 3.7- and 88.0-fold higher in OT than in controls (P = 0.04 and P = 0.03, respectively) whereas that of TGF-β was 7.7-fold lower (P < 0.001). The expression levels for these cytokines in PBMC followed a similar pattern (IL-10 13.8-fold down-regulated (P = 0.001), IL-17 with 1.9-fold insignificantly upregulated (p = 0.43), TGF-β 452.8-fold down-regulated (P = 0.002). Compared to PBMC, IL-10 coding mRNA was 1876-fold higher in the almost cell-free AH in OT (39.2-fold in controls), IL-17 coding mRNA was 9.4-fold higher (17.7-fold down-regulated in controls), and that coding for TGF-β 207-fold higher in OT (7x105-fold in controls). The expression for IL-10, IL-17 and TGF-β in AH thus followed an opposite pattern compared to that in PBMC.OT induces a highly-specific local immunoregulatory process as evidenced by an intraocular up-regulation of IL-10 and down-regulation of TGF-β mRNA. This could indicate an attempt to prevent unnecessary tissue damage which is in line with a moderate local mRNA up-regulation for IL-17 which seems sufficient to control parasite proliferation. That this regulation is opposite to that in PBMC may be linked to intraocular immune deviation in the course of disease.

Congenital toxoplasmic retinochoroiditis in a mouse model.

A study of the eyes of adult mice infected in utero with Toxoplasma gondii is reported. The histopathological features of the ocular inflammatory response in the infected mice ranged from minimal damage to complete destruction of the retinal tissue. Notable features such as retinal vasculitis and an almost uniform and highly selective destruction of the photoreceptor layer of the retina suggest a similarity between experimental autoimmune retinitis and the disease process in the retinas of our Toxoplasma-infected mice. We suggest that our mouse model could provide a simple and inexpensive tool for the investigation of immuno-pathological processes in the retina resulting from congenital Toxoplasma infection. The model has the advantage of low post-natal mortality coupled with high ocular morbidity. Furthermore, its aetiology is probably analogous to that of human ocular toxoplasmosis, in that the foetus becomes infected in utero via a mother whose primary infection is acquired during gestation.

Experimental ocular toxoplasmosis in primates.

The rabbit serves as the only existing experimental model for ocular toxoplasmosis. This model has many deficiencies. Our technique for the production of acute toxoplasmic retinitis in monkeys is described herein. This primate model should be more representative than the rabbit model of human ocular toxoplasmosis.

CLINDAMYCIN IN HUMAN OCULAR TOXOPLASMOSIS: A PRELIMINARY REPORT

SummaryAn initial clinical impression on the therapeutic effectiveness of clindamycin in human ocular toxoplasmosis is reported. Fourteen patients have been treated with clindamycin, a chemical analogue of lincomycin. All patients responded satisfactorily to therapy, with 71.4% of the patients responding within the first week of treatment. In most cases normal to near normal visual acuities were restored. No serious gastro‐intestinal side effects were seen. One patient developed rashes.

Treatment of toxoplasmosis uveitis.

<h3>Introduction</h3> In recent years toxoplasmosis has come to be recognized as the most important etiologic condition of the granulomatous type of uveitis.^1,2Our group has attributed 44% of all of our uveitis cases to toxoplasmosis.³Hand in hand with this trend the search for an effective therapy for this condition has been going on. To date, the combination of pyrimethamine (Daraprim) and the sulfa drugs seems to be most effective. This had been brought about by the observation of Eyles and Coleman⁴on the synergistic actions of these drugs against toxoplasmosis in experimental animals. Ryan, et al.,⁵Jacobs, et al.,^6aand Perkins^6bshowed that this combination can be used successfully in human ocular toxoplasmosis. The results were thought to be improved when a systemic steroid was added.^7,8 Because of the toxicity encountered by the use of these drugs various antibiotics have been screened