T-cell profiles elicited by Toxoplasma gondii in acutely/chronically infected humans

Cytotoxic Signature and IFN-γ Production Dominate CD4+ T-Cell Response During Human Toxoplasmosis

Toxoplasma gondii is a highly versatile parasite that infects most warm-blooded animals and is a major cause of retinochoroiditis and uveitis in humans. The pathophysiology of these conditions remains poorly understood. Both parasite virulence and host inflammatory response contribute to the development of ocular disease. While CD4+ T cells play a critical role in host resistance to Toxoplasma infection, their kinetics and effector functions, as well as their contribution to the clinical outcome of the infection, including ocular involvement, remain poorly understood. To address this question, we investigated the immune response during acute and convalescent toxoplasmosis and stratified patients further based on the presence or absence of ocular disease. We found that T. gondii infection leads to decreased and increased proportions of central and effector memory CD4+ T cells, respectively. Applying unsupervised analysis, distinct CD4+ T-cell subsets were determined. Among 50 clusters, 10 produced cytotoxic proteins (granzyme B and perforin) and one produced cytokines upon antigen-specific stimulation. We observed that proportions of five CD4+ T-cell clusters out of 50 were different during acute disease between T. gondii-infected patients with and without ocular lesions. Interestingly, three of the five displayed a cytotoxic signature indicating their possible involvement in ocular immunopathology. Taken together, our results reveal that during T. gondii infection, CD4+ T cells not only develop a Th1 cytokine profile, but also acquire previously unappreciated cytotoxic capacity/function. These results, while underscoring the complexity of the CD4+ T-cell response to T. gondii, suggest that specific subsets may be involved in the development of pathology and provide possible targets for therapeutic intervention.

Detection of toxoplasmic encephalitis in HIV positive patients in urine with hydrogel nanoparticles

BACKGROUND

Diagnosis of toxoplasmic encephalitis (TE) is challenging under the best clinical circumstances. The poor clinical sensitivity of quantitative polymerase chain reaction (qPCR) for Toxoplasma in blood and CSF and the limited availability of molecular diagnostics and imaging technology leaves clinicians in resource-limited settings with few options other than empiric treatment.

METHOLOGY/PRINCIPLE FINDINGS

Here we describe proof of concept for a novel urine diagnostics for TE using Poly-N-Isopropylacrylamide nanoparticles dyed with Reactive Blue-221 to concentrate antigens, substantially increasing the limit of detection. After nanoparticle-concentration, a standard western blotting technique with a monoclonal antibody was used for antigen detection. Limit of detection was 7.8pg/ml and 31.3pg/ml of T. gondii antigens GRA1 and SAG1, respectively. To characterize this diagnostic approach, 164 hospitalized HIV-infected patients with neurological symptoms compatible with TE were tested for 1) T. gondii serology (121/147, positive samples/total samples tested), 2) qPCR in cerebrospinal fluid (11/41), 3) qPCR in blood (10/112), and 4) urinary GRA1 (30/164) and SAG1 (12/164). GRA1 appears to be superior to SAG1 for detection of TE antigens in urine. Fifty-one HIV-infected, T. gondii seropositive but asymptomatic persons all tested negative by nanoparticle western blot and blood qPCR, suggesting the test has good specificity for TE for both GRA1 and SAG1. In a subgroup of 44 patients, urine samples were assayed with mass spectrometry parallel-reaction-monitoring (PRM) for the presence of T. gondii antigens. PRM identified antigens in 8 samples, 6 of which were concordant with the urine diagnostic.

CONCLUSION/SIGNIFICANCES

Our results demonstrate nanoparticle technology's potential for a noninvasive diagnostic test for TE. Moving forward, GRA1 is a promising target for antigen based diagnostics for TE.

Key Limitations and New Insights Into the Toxoplasma gondii Parasite Stage Switching for Future Vaccine Development in Human, Livestock, and Cats

Toxoplasmosis is a parasitic disease affecting human, livestock and cat. Prophylactic strategies would be ideal to prevent infection. In a One Health vaccination approach, the objectives would be the prevention of congenital disease in both women and livestock, prevention/reduction of T. gondii tissue cysts in food-producing animals; and oocyst shedding in cats. Over the last few years, an explosion of strategies for vaccine development, especially due to the development of genetic-engineering technologies has emerged. The field of vaccinology has been exploring safer vaccines by the generation of recombinant immunogenic proteins, naked DNA vaccines, and viral/bacterial recombinants vectors. These strategies based on single- or few antigens, are less efficacious than recombinant live-attenuated, mostly tachyzoite T. gondii vaccine candidates. Reflections on the development of an anti-Toxoplasma vaccine must focus not only on the appropriate route of administration, capable of inducing efficient immune response, but also on the choice of the antigen (s) of interest and the associated delivery systems. To answer these questions, the choice of the animal model is essential. If mice helped in understanding the protection mechanisms, the data obtained cannot be directly transposed to humans, livestock and cats. Moreover, effectiveness vaccines should elicit strong and protective humoral and cellular immune responses at both local and systemic levels against the different stages of the parasite. Finally, challenge protocols should use the oral route, major natural route of infection, either by feeding tissue cysts or oocysts from different T. gondii strains. Effective Toxoplasma vaccines depend on our understanding of the (1) protective host immune response during T. gondii invasion and infection in the different hosts, (2) manipulation and modulation of host immune response to ensure survival of the parasites able to evade and subvert host immunity, (3) molecular mechanisms that define specific stage development. This review presents an overview of the key limitations for the development of an effective vaccine and highlights the contributions made by recent studies on the mechanisms behind stage switching to offer interesting perspectives for vaccine development.

Toxoplasma Gondii Infection and a History of Surgery: A Case Control Seroprevalence Study

We determined the association between having a history of surgery and the seroreactivity to T. gondii. An age- and gender-matched case-control study of 391 subjects with a history of surgery and 391 subjects without this history was performed. Sera of subjects were analyzed for detection of anti-T. gondii immunoglobulin G (IgG) and M (IgM) antibodies using enzyme-linked immunoassays. Anti-T. gondii IgG antibodies were found in 25 (6.4%) of the 391 cases and in 21 (5.4%) of the 391 controls (odds ratio [OR] = 1.29; 95% confidence interval [CI]: 0.66-2.18; P = 0.54). The frequency of cases with high IgG antibody levels (10/25: 40.0%) was equal to that found in controls (8/21: 38.1%) (OR = 1.08; 95% CI: 0.32-3.56; P = 0.89). Of the 25 anti-T. gondii IgG antibody seropositive cases, 5 (16.0%) were also positive for anti-T. gondii IgM antibodies. Meanwhile, of the 21 anti-T. gondii IgG antibody seropositive controls, 4 (19.0%) were also positive for anti-T gondii IgM antibodies (OR = 0.81; 95% CI: 0.17-3.72; P = 0.80). Logistic regression showed that only the variable "hysterectomy" was associated with T. gondii seropositivity (OR = 4.6; 95% CI: 1.6-13.4; P = 0.005). Results suggest that having a history of surgery is not an important risk factor for infection with T. gondii. However, the link between T. gondii infection and hysterectomy should be further investigated.