Toxoplasma gondii: CD8 T Cells Cry for CD4 Help

Biophysical and biochemical aspects of immune cell-tumor microenvironment interactions

The tumor microenvironment (TME), composed of and influenced by a heterogeneous set of cancer cells and an extracellular matrix, plays a crucial role in cancer progression. The biophysical aspects of the TME (namely, its architecture and mechanics) regulate interactions and spatial distributions of cancer cells and immune cells. In this review, we discuss the factors of the TME-notably, the extracellular matrix, as well as tumor and stromal cells-that contribute to a pro-tumor, immunosuppressive response. We then discuss the ways in which cells of the innate and adaptive immune systems respond to tumors from both biochemical and biophysical perspectives, with increased focus on CD8+ and CD4+ T cells. Building upon this information, we turn to immune-based antitumor interventions-specifically, recent biophysical breakthroughs aimed at improving CAR-T cell therapy.

New advances in immune mechanism and treatment during ocular toxoplasmosis

Ocular toxoplasmosis (OT) is an intraocular infection caused by the parasite Toxoplasma gondii. OT is manifested as retinal choroiditis and is the most common infectious cause of posterior uveitis. Invasion of the retina by T. gondii leads to disruption of the blood-ocular barrier and promotes the migration of immune cells to the ocular tissues. Cytokines such as IFN-γ and IL-1β are effective for controlling parasite growth, but excessive inflammatory responses can cause damage to the host. In this review, we will discuss in detail the latest advances in the immunopathology and treatment of OT.

Improved ELISPOT protocol for monitoring Th1/Th17 T-cell response following T.gondii infection

In the monitoring of human Toxoplasma gondii infection, it is crucial to confirm the development of a specific Th1/Th17 immune response memory. The use of a simple, specific, and sensitive assay to follow the T-cell activation is thus required. Current protocols are not always specific as stimulation with peptides is Human Leukocyte Antigen (HLA)-dependent, while stimulation with total-lysis antigens tends to stimulate seronegative donors resulting to false positives. Here, an improved ELISPOT protocol is reported, using peripheral blood mononuclear cells (PBMC) of T.gondii-infected donors, incubated with the inactivated parasite. The results showed that, contrary to standard protocols, a pre-incubation step at high cell density in presence of the inactivated parasite allowed a specific Th1/Th17 response with the secretion of IFN-γ, IL-2, IL-12 and IL-17 cytokines. This protocol allows to evaluate precisely the immune response after a T.gondii infection.

Exploring the potential of Toxoplasma gondii in drug development and as a delivery system

Immune-mediated inflammatory diseases are various groups of conditions that result in immune system disorders and increased cancer risk. Despite the identification of causative cytokines and pathways, current clinical treatment for immune-mediated inflammatory diseases is limited. In addition, immune-mediated inflammatory disease treatment can increase the risk of cancer. Several previous studies have demonstrated that Toxoplasma gondii manipulates the immune response by inhibiting or stimulating cytokines, suggesting the potential for controlling and maintaining a balanced immune system. Additionally, T. gondii also has the unique characteristic of being a so-called "Trojan horse" bacterium that can be used as a drug delivery system to treat regions that have been resistant to previous drug delivery therapies. In this study, we reviewed the potential of T. gondii in drug development and as a delivery system through current research on inflammation-regulating mechanisms in immune-mediated inflammatory diseases.

A pre-existing Toxoplasma gondii infection exacerbates the pathophysiological response and extent of brain damage after traumatic brain injury in mice

Traumatic brain injury (TBI) is a key contributor to global morbidity that lacks effective treatments. Microbial infections are common in TBI patients, and their presence could modify the physiological response to TBI. It is estimated that one-third of the human population is incurably infected with the feline-borne parasite, Toxoplasma gondii, which can invade the central nervous system and result in chronic low-grade neuroinflammation, oxidative stress, and excitotoxicity-all of which are also important pathophysiological processes in TBI. Considering the large number of TBI patients that have a pre-existing T. gondii infection prior to injury, and the potential mechanistic synergies between the conditions, this study investigated how a pre-existing T. gondii infection modified TBI outcomes across acute, sub-acute and chronic recovery in male and female mice. Gene expression analysis of brain tissue found that neuroinflammation and immune cell markers were amplified in the combined T. gondii + TBI setting in both males and females as early as 2-h post-injury. Glutamatergic, neurotoxic, and oxidative stress markers were altered in a sex-specific manner in T. gondii + TBI mice. Structural MRI found that male, but not female, T. gondii + TBI mice had a significantly larger lesion size compared to their uninfected counterparts at 18-weeks post-injury. Similarly, diffusion MRI revealed that T. gondii + TBI mice had exacerbated white matter tract abnormalities, particularly in male mice. These novel findings indicate that a pre-existing T. gondii infection affects the pathophysiological aftermath of TBI in a sex-dependent manner, and may be an important modifier to consider in the care and prognostication of TBI patients.

Recombinant antigen P29 of Echinococcus granulosus induces Th1, Tc1, and Th17 cell immune responses in sheep

Echinococcosis is a common human and animal parasitic disease that seriously endangers human health and animal husbandry. Although studies have been conducted on vaccines for echinococcosis, to date, there is no human vaccine available for use. One of the main reasons for this is the lack of in-depth research on basic immunization with vaccines. Our previous results confirmed that recombinant antigen P29 (rEg.P29) induced more than 90% immune protection in both mice and sheep, but data on its induction of sheep-associated cellular immune responses are lacking. In this study, we investigated the changes in CD4+ T cells, CD8+ T cells, and antigen-specific cytokines IFN-γ, IL-4, and IL-17A after rEg.P29 immunization using enzyme-linked immunospot assay (ELISPOT), enzyme-linked immunosorbent assay (ELISA), and flow cytometry to investigate the cellular immune response induced by rEg.P29 in sheep. It was found that rEg.P29 immunization did not affect the percentage of CD4+ and CD8+ T cells in peripheral blood mononuclear cells (PBMCs), and was able to stimulate the proliferation of CD4+ and CD8+ T cells after immunization in vitro. Importantly, the results of both ELISPOT and ELISA showed that rEg.P29 can induce the production of the specific cytokines IFN-γ and IL-17A, and flow cytometry verified that rEg.P29 can induce the expression of IFN-γ in CD4+ and CD8+ T cells and IL-17A in CD4+ T cells; however, no IL-4 expression was observed. These results indicate that rEg.P29 can induce Th1, Th17, and Tc1 cellular immune responses in sheep against echinococcosis infection, providing theoretical support for the translation of rEg.P29 vaccine applications.

Immune system roles in pathogenesis, prognosis, control, and treatment of Toxoplasma gondii infection

Toxoplasma gondii is the protozoan causative agent of toxoplasmosis in humans and warm-blooded animals. Recent studies have illustrated that the immune system plays a pivotal role in the pathogenesis of toxoplasmosis by triggering immune cytokines like IL-12, TNF-α, and IFN-γ and immune cells like DCs, Th1, and Th17. On the other hand, some immune components can serve as prognosis markers of toxoplasmosis. In healthy people, the disease is often asymptomatic, but immunocompromised people and newborns may suffer severe symptoms and complications. Therefore, the immune prognostic markers may provide tools to measure the disease progress and help patients to avoid further complications. Immunotherapies using monoclonal antibody, cytokines, immune cells, exosomes, novel vaccines, and anti-inflammatory molecules open new horizon for toxoplasmosis treatment. In this review article, we discussed the immunopathogenesis, prognosis, and immunotherapy of Toxoplasma gondii infection.

Association between breakthrough infection with COVID-19 and Toxoplasma gondii: a cross-sectional study

The breakthrough infection following COVID-19 vaccination has been a subject of concern recently. Evidence suggests that COVID-19 vaccine efficacy diminishes over time due to multiple factors related to the host, and vaccine. Coinfection with other pathogens was claimed earlier as a contributing cause for this phenomenon. Hence, we aimed to stratify the association of post-COVID-19 vaccination breakthrough coinfection with Toxoplasma gondii (T. gondii) and its impact on disease severity. This cross-sectional study included 330 COVID-19-vaccinated patients confirmed by RT-PCR. They were also screened for anti- T. gondii antibodies using ELISA. Toxoplasma seropositive cases' whole blood was screened for DNA using PCR to correlate results with COVID-19 severity. Out of 330 COVID-19 vaccinated patients with breakthrough infection, 34.5% (114 patients) showed positivity for Toxoplasma IgG by ELISA, and none of the cases was IgM positive. Eleven patients (9.6%) of the IgG-positive cases were positive by PCR. Positive PCR cases correlated positively with the Toxoplasma IgG titer (P < 0.001), and the Cutoff point was 191.5. Molecular analysis of Toxoplasma and COVID-19 severity showed that 8 (72.7%), 1 (9.1%), and 2 cases (18.2%) had mild, moderate, and severe courses of the disease, respectively, with no significant correlation. Our study reported a heightened prevalence of latent toxoplasmosis among mild cases of COVID-19 breakthrough infection. Nevertheless, a discernible correlation between latent toxoplasmosis and COVID-19 severity is lacking. Hence, implementing studies on a larger scale could provide a more comprehensive comprehension of this association.

Biogenic selenium nanoparticles: trace element with promising anti-toxoplasma effect

Toxoplasmosis is an opportunistic infection caused by the coccidian Toxoplasma gondii which represents a food and water contaminant. The available chemotherapeutic agents for toxoplasmosis are limited and the choice is difficult when considering the side effects. Selenium is an essential trace element. It is naturally found in dietary sources, especially seafood, and cereals. Selenium and selenocompounds showed anti-parasitic effects through antioxidant, immunomodulatory, and anti-inflammatory mechanisms. The present study evaluated the potential efficacy of environmentally benign selenium nanoparticles (SeNPs) against acute toxoplasmosis in a mouse model. SeNPs were fabricated by nanobiofactory Streptomyces fulvissimus and characterized by different analytical techniques including, UV-spectrophotometry, transmission electron microscopy, EDX, and XRD. Swiss albino mice were infected with Toxoplasma RH strain in a dose of 3500 tachyzoites in 100 μl saline to induce acute toxoplasmosis. Mice were divided into five groups. Group I: non-infected, non-treated, group II: infected, non-treated, group III: non-infected, treated with SeNPs, group IV: infected, treated with co-trimoxazole (sulfamethoxazole/trimethoprim) and group V: infected, treated with SeNPs. There was a significant increase in survival time in the SeNPs-treated group and minimum parasite count was observed compared to untreated mice in hepatic and splenic impression smears. Scanning electron microscopy showed tachyzoites deformity with multiple depressions and protrusions, while transmission electron microscopy showed excessive vacuolization and lysis of the cytoplasm, especially in the area around the nucleus and the apical complex, together with irregular cell boundary and poorly demarcated cell organelles. The present study demonstrated that the biologically synthesized SeNPs can be a potential natural anti-Toxoplasma agent in vivo.

Comparative evaluation of cell-mediated immune response in calves immunized with live-attenuated and killed Theileria annulata vaccines

Tropical theileriosis is a tick-borne disease caused by the protozoan Theileria annulata and transmitted by numerous species of Ixodid ticks of the genus Hyalomma. The main clinical signs are fever, lymphadenopathy, and anemia responsible for heavy economic losses, including mortality, morbidity, vaccination failure, and treatment cost. Development of poor cell-mediated immunity (CMI) has been observed in the case of many bovine pathogens (bacteria, viruses, and parasites). Quantification of CMI is a prerequisite for evaluating vaccine efficacy against theileriosis caused by T. annulata. The current study evaluated the CMI in calves administered with two types of T. annulata vaccine (live attenuated and killed). We prepared a live attenuated T. annulata vaccine by attenuation in a rabbit model and also prepared killed vaccine from non-attenuated T. annulata. For the evaluation of immune response in experimental groups including control, 20 calves were divided into four different groups (A, B, C, and D). They were either inoculated subcutaneously with live rabbit-propagated-Theileria-infected RBCs (5 × 106) (group A) or with killed T. annulata vaccine (2 × 109 schizonts) with Freund's adjuvant (group B), along with an infected group (group C) and a healthy control group (group D). The protection of vaccinated calves was estimated with challenge infection. Our results showed that with a single shot of live-attenuated and killed vaccine with a booster dose elicited cell-mediated immune responses in immunized calves. We observed a significant elevation in CD4 + and CD8 + T cells in immunized calves. A significant difference in the CD8 + T cell response between the post-challenge stage of killed and live vaccine (p < 0.0001) was observed, whereas no other difference was found at both pre- and post-immunization stages. A similar finding was recorded for the CD4 + T cells at a post-challenge stage, where a significant difference was seen between killed and live vaccine (p < 0.0001). Another significant difference was observed between the CD8 + T cells and CD4 + T cells at the post-challenge stage in the live vaccine group, where there was a significantly higher induction of CD4 + T cell response (p < 0.0001).

Influenza A Virus Weakens the Immune Response of Mice to Toxoplasma gondii, Thereby Aggravating T. gondii Infection

This study aimed to investigate the relationship between the T. gondii type II strain (Pru) and respiratory viral infections, specifically focusing on the co-infection with PR8 (influenza A/Puerto Rico/8/34). In this study, we found that the number of T. gondii (Pru) in the lungs of co-infected mice was significantly higher and lesions were more severe than those in the group infected with T. gondii (Pru) alone, whereas IAV (influenza A virus) copy numbers of co-infected and PR8 alone infected groups were negligible, suggesting that infection with IAV increased the pathogenicity of T. gondii (Pru) in mice. The invasion and proliferation assays demonstrated no significant effect of co-infection on T. gondii (Pru) infection or replication in vitro. To further explore the factors causing the altered pathogenicity of T. gondii (Pru) caused by co-infection, we found that decreased expression levels of IL-1β, IL-6, and IL-12 in the co-infected group were associated with the early immune responses against T. gondii (Pru), which affected the division of T. gondii (Pru). Moreover, the significant decrease in the CD4⁺/CD8⁺ ratio indicated a weakened long-term immune killing ability of the host against T. gondii (Pru) following IAV infection. In conclusion, a T. gondii type II strain (Pru) could not be properly cleared by the host immune system after IAV infection, resulting in toxoplasmosis and even death in mice.

From the immune system to mood disorders especially induced by Toxoplasma gondii: CD4+ T cell as a bridge

Toxoplasma gondii (T. gondii), a ubiquitous and obligatory intracellular protozoa, not only alters peripheral immune status, but crosses the blood-brain barrier to trigger brain parenchymal injury and central neuroinflammation to establish latent cerebral infection in humans and other vertebrates. Recent findings underscore the strong correlation between alterations in the peripheral and central immune environment and mood disorders. Th17 and Th1 cells are important pro-inflammatory cells that can drive the pathology of mood disorders by promoting neuroinflammation. As opposed to Th17 and Th1, regulatory T cells have inhibitory inflammatory and neuroprotective functions that can ameliorate mood disorders. T. gondii induces neuroinflammation, which can be mediated by CD4+ T cells (such as Tregs, Th17, Th1, and Th2). Though the pathophysiology and treatment of mood disorder have been currently studied, emerging evidence points to unique role of CD4+ T cells in mood disorder, especially those caused by T. gondii infection. In this review, we explore some recent studies that extend our understanding of the relationship between mood disorders and T. gondii.

A Lower Dose of Infection Generates a Better Long-Term Immune Response against Toxoplasma gondii

Toxoplasma gondii, an obligate intracellular pathogen, induces a strong immune response in the infected host. In the encephalitis model of infection, long-term protective immunity is mediated by CD8 T cells, with the CD4 T cell population providing important help. Most of the immune studies have used a 10- to 20-cyst dose of T. gondii, which leads to T cell dysfunctionality during the late phase of chronic infection and increases the chances of reactivation. In the current study, we compared the immune response of mice orally infected with either 2 or 10 cysts of T. gondii. During the acute phase, we demonstrate that the lower dose of infection generates a reduced number of CD4 and CD8 T cells, but the frequency of functional CD4 or CD8 T cells is similar in animals infected with two different doses. However, Ag-experienced T cells (both CD4 and CD8) are better maintained in lower dose-infected mice at 8 wk postinfection, with an increase number functional cells that exhibit lower multiple inhibitory receptor expression. In addition to better long-term T cell immunity, animals infected with a lower dose display reduced inflammation manifested by lesser Ag-specific T cell and cytokine responses during the very early stage of the acute infection. Our studies suggest a previously unappreciated role of dose-dependent early programming/imprinting of the long-term CD4/CD8 T cell response during T. gondii infection. These observations point to the need for an in-depth analysis of how early events shape long-term immunity against this pathogen.

Advances and Challenges in Diagnostics of Toxoplasmosis in HIV-Infected Patients

Toxoplasma gondii is a worldwide distributed protozoan parasite. This apicomplexan parasite infects one-third of the population worldwide, causing toxoplasmosis, considered one of the neglected parasitic infections. In healthy humans, most infections are asymptomatic. However, in immunocompromised patients, the course of the disease can be life-threatening. Human immunodeficiency virus (HIV)-infected patients have a very high burden of Toxoplasma gondii co-infection. Thus, it is essential to use modern, sensitive, and specific methods to properly monitor the course of toxoplasmosis in immunodeficient patients.

Toxoplasma gondii vaccine candidates: a concise review

Toxoplasma gondii is an obligate intracellular parasite that causes toxoplasmosis. It has been shown that the severity of symptoms depends on the functioning of the host immune system. Although T. gondii infection typically does not lead to severe disease in healthy people and after infection, it induces a stable immunity, but it can contribute to severe and even lethal Toxoplasmosis in immunocompromised individuals (AIDS, bone marrow transplant and neoplasia). The antigens that have been proposed to be used in vaccine candidate in various studies include surface antigens and secretory excretions that have been synthesized and evaluated in different studies. In some studies, secretory antigens play an important role in stimulating the host immune response. Various antigens such as SAG, GRA, ROP, ROM, and MAG have been from different strains of T. gondii have been synthesized and their protective effects have been evaluated in animal models in different vaccine platforms including recombinant antigens, nanoparticles, and DNA vaccine. Four bibliographic databases including Science Direct, PubMed Central (PMC), Scopus, and Google Scholar were searched for articles published up to 2020.The current review article focuses on recent studies on the use and usefulness of recombinant antigens, nanoparticles, and DNA vaccines.

Regulation of piglet T-cell immune responses by thioredoxin peroxidase from Cysticercus cellulosae excretory-secretory antigens

Taenia solium (T. solium) cysticercosis is a serious threat to human health and animal husbandry. During parasitization, Cysticercus cellulosae (C. cellulosae) can excrete and secrete antigens that modulate the host's T-cell immune responses. However, the composition of C. cellulosae excretory-secretory antigens (ESAs) is complex. This study sought to identify the key molecules in C. cellulosae ESAs involved in regulating T-cell immune responses. Thus, we screened for thioredoxin peroxidase (TPx), with the highest differential expression, as the key target by label-free quantification proteomics of C. cellulosae and its ESAs. In addition, we verified whether TPx protein mainly exists in C. cellulosae ESAs. The TPx recombinant protein was prepared by eukaryotic expression, and ESAs were used as the experimental group to further investigate the effect of TPx protein on the immune response of piglet T cells in vitro. TPx protein induced an increase in CD4+ T cells in piglet peripheral blood mononuclear cells (PBMCs), while CD8+ T cells did not change significantly. This resulted in an imbalance in the CD4+/CD8+ T-cell ratio and an increase in CD4+CD25+Foxp3+ Treg cells in the PBMCs. In addition, TPx protein initiated T helper 2 (Th2)-type immune responses by secreting IL-4 and IL-10 and suppressed Th1/Th17-type immune responses. The results showed that ESAs were involved in regulating piglet T-cell immune responses cells. This suggests that TPx protein found in ESAs plays an essential role to help the parasite evade host immune attack. Moreover, this lays a foundation for the subsequent exploration of the mechanism through which TPx protein regulates signaling molecules to influence T-cell differentiation.

Protection Induced by Vaccination with Recombinant Baculovirus and Virus-like Particles Expressing Toxoplasma gondii Rhoptry Protein 18

Heterologous immunization is garnering attention as a promising strategy to improve vaccine efficacy. Vaccines based on recombinant baculovirus (rBV) and virus-like particle (VLP) are safe for use, but heterologous immunization studies incorporating these two vaccine platforms remain unreported to date. Oral immunization is the simplest, most convenient, and safest means for mass immunization. In the present study, mice were immunized with the Toxoplasma gondii rhoptry protein 18 (ROP18)-expressing rBVs (rBVs-ROP18) and VLPs (VLPs-ROP18) via oral, intranasal, and intramuscular (IM) routes to evaluate the protection elicited against the intracellular parasite T. gondii ME49 strain. Overall, boost immunization with VLPs-ROP18 induced a significant increase in T. gondii-specific antibody response in all three immunization routes. Parasite-specific mucosal and cerebral antibody responses were observed from all immunization groups, but the highest mucosal IgA response was detected from the intestines of orally immunized mice. Antibody-secreting cell (ASC), CD8⁺ T cell, and germinal center B cell responses were strikingly similar across all three immunization groups. Oral immunization significantly reduced pro-inflammatory cytokine IL-6 in the brains as well as that by IN and IM. Importantly, all of the immunized mice survived against lethal challenge infections where body weight loss was negligible from all three immunizations. These results demonstrated that protection induced against T. gondii by oral rBV-VLP immunization regimen is just as effective as IN or IM immunizations.

Association of gestational diabetes mellitus and negative modulation of the specific humoral and cellular immune response against Toxoplasma gondii

In order to evaluate and compare the specific immune response of pregnant women (PW) chronically infected with Toxoplasma gondii, with and without gestational diabetes mellitus (GDM), and the humoral response of their respective newborns (NB), the study was carried out on 81 PW (34 GDM and 47 controls) from whose medical records the results of the oral glucose tolerance test (OGTT) were obtained, and blood samples were collected at the third trimester of pregnancy; also, on 45 NBs (20 GDM and 25 controls) from whom umbilical cord blood samples were obtained. Humoral immunity was analyzed by measuring anti-T. gondii total IgG, IgG subclasses and IgG avidity. To evaluate cellular immunity, peripheral blood mononuclear cells (PBMC) from 32 PW (16 GDM and 16 controls) were cultured, supernatant cytokines were determined, and flow cytometry was performed to analyze the expression at lymphocytes of surface molecules, cytokines and transcription factors. All PW and NBs were positive for total IgG, and the prevalent subclass was IgG1. There was a negative correlation between the OGTT glycemia of PW and the levels of total IgG, IgG1 and IgG avidity. The IgG avidity of the GDM group was significantly lower than the control group. Patients from the GDM group had a higher number of T lymphocytes expressing markers of cell activation and exhaustion (CD28 and PD-1). In the presence of T. gondii soluble antigen (STAg) the amount of CD4+ T cells producing IFN-γ, IL-10 and IL-17 was significantly lower in the GDM group, while there was no difference between groups in the number of CD4+ CD25HighFOXP3+LAP+ functional Treg cells. Additionally, under STAg stimulus, the secretion of IL-17, IL-4, TNF and IL-2 cytokines at PBMCs culture supernatant was lower in the GDM group. In conclusion, there was a correlation between the increase in blood glucose and the decrease in levels of anti-T. gondii antibodies, associated with the decreased IgG avidity in patients who develop GDM. Also, the GDM group had decreased immune responses in Th1, Th2 and Th17 profiles, suggesting an association between GDM and the negative modulation of the humoral and cellular immune responses against T. gondii.

Building Programs to Eradicate Toxoplasmosis Part I: Introduction and Overview

Purpose of Review

Review building of programs to eliminate Toxoplasma infections.

Recent Findings

Morbidity and mortality from toxoplasmosis led to programs in USA, Panama, and Colombia to facilitate understanding, treatment, prevention, and regional resources, incorporating student work.

Summary

Studies foundational for building recent, regional approaches/programs are reviewed. Introduction provides an overview/review of programs in Panamá, the United States, and other countries. High prevalence/risk of exposure led to laws mandating testing in gestation, reporting, and development of broad-based teaching materials about Toxoplasma. These were tested for efficacy as learning tools for high-school students, pregnant women, medical students, physicians, scientists, public health officials and general public. Digitized, free, smart phone application effectively taught pregnant women about toxoplasmosis prevention. Perinatal infection care programs, identifying true regional risk factors, and point-of-care gestational screening facilitate prevention and care. When implemented fully across all demographics, such programs present opportunities to save lives, sight, and cognition with considerable spillover benefits for individuals and societies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40124-022-00269-w.

Building Programs to Eradicate Toxoplasmosis Part IV: Understanding and Development of Public Health Strategies and Advances “Take a Village”

Purpose of Review

Review international efforts to build a global public health initiative focused on toxoplasmosis with spillover benefits to save lives, sight, cognition and motor function benefiting maternal and child health.

Recent Findings

Multiple countries’ efforts to eliminate toxoplasmosis demonstrate progress and context for this review and new work.

Summary

Problems with potential solutions proposed include accessibility of accurate, inexpensive diagnostic testing, pre-natal screening and facilitating tools, missed and delayed neonatal diagnosis, restricted access, high costs, delays in obtaining medicines emergently, delayed insurance pre-approvals and high medicare copays taking considerable physician time and effort, harmful shortcuts being taken in methods to prepare medicines in settings where access is restricted, reluctance to perform ventriculoperitoneal shunts promptly when needed without recognition of potential benefit, access to resources for care, especially for marginalized populations, and limited use of recent advances in management of neurologic and retinal disease which can lead to good outcomes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40124-022-00268-x.

Immune responses to Toxoplasma gondii

Toxoplasma gondii is an obligate intracellular parasite that can cause severe complications in the newborn and immunocompromised individuals. The parasite evokes a strong innate immune response in the infected hosts which is followed by a robust adaptive immunity. In the last few years, importance of innate immune mechanisms dependent on the role of MyD-88 independent pathways, inflammatory monocytes and innate lymphocyte have been identified. However, notwithstanding the strong immune response to the parasite, the chronic infection persists in the host. The inability to prevent chronic infection can be attributed to aberration in the memory CD8 T cell response caused by an increased expression of inhibitory receptors that leads to their dysfunctionality.

Role of the PD-1/PD-L1 Pathway in Experimental Trypanosoma cruzi Infection and Potential Therapeutic Options

Chagas disease (CD) is a neglected chronic infection caused by the protozoan parasite Trypanosoma cruzi (T. cruzi). A significant portion of infected people develops cardiac or digestive alterations over a lifetime. Since several chronic infections associated with antigen persistence and inflammation have been shown to lead to T cell exhaustion, new therapies targeting co-inhibitory receptors to regain T cell activity are under consideration. This study explored immune therapeutic approaches targeting the inhibitory PD-1/PD-L pathway in an experimental model for CD. Infected PD-L1 knockout mice (PD-L1 KO) showed increased systemic parasitemia in blood although no significant differences in parasite load were observed in different organs. Furthermore, we found no significant differences in the frequency of activated T cells or proinflammatory cytokine production when compared to WT counterparts. PD-L1 deficiency led to the production of IL-10 by CD8⁺ T cells and an upregulation of Tim-3 and CD244 (2B4). Unexpectedly, the lack of PD-L1 did not contribute to a significantly improved T cell response to infection. Single blockade and combined blockade of PD-1 and Tim-3 using monoclonal antibodies confirmed the results observed in infected. PD-L1 KO mice. Our results describe for the first time that the interruption of the PD-1/PD-L1 axis during acute T. cruzi infection does not necessarily enhance the immune response against this parasite. Its interruption favors increased levels of parasitemia and sustained upregulation of other co-inhibitory receptors as well as the production of regulatory cytokines. These results suggest that the clinical application of immune therapeutic approaches targeting the PD-1/PD-L1 axis in CD might be risky and associated with adverse events. It highlights that more research is urgently needed to better understand the immune regulation of T cells in CD before designing immune therapeutic approaches for a clinical context.

Exhausted PD-1+ TOX+ CD8+ T Cells Arise Only in Long-Term Experimental Trypanosoma cruzi Infection

Infection with Trypanosoma cruzi remains the most important neglected zoonosis in Latin America. This infection does not lead to specific symptoms in the acute phase, but chronic infection can result in Chagas disease (CD) with cardiac and/or gastrointestinal manifestations that can lead to death. CD8⁺ T cells are highly effective and essential to control this infection, but fail to eliminate all parasites. In this study, we show that the CD8⁺ T cells are modulated by the transient induction of co-inhibitory receptors during acute infection of C57BL/6 mice. Therapeutic intervention strategies with blocking antibodies only had a marginal effect on the elimination of parasite reservoirs. Only long-term chronic infection gave rise to dysfunctional CD8⁺ T cells, which were characterized by high expression of the inhibitory receptor PD-1 and the co-expression of the transcription factor TOX, which plays a crucial role in the maintenance of the exhausted phenotype. PD-1⁺ TOX⁺ CD8⁺ T cells isolated from the site of infection produced significantly less IFN-γ, TNF-α and Granzyme B than their PD-1^- TOX^- CD8⁺ T cell counterparts after T. cruzi-specific stimulation ex vivo. Taken together, we provide evidence that, in the context of experimental infection of mice, the magnitude of the CD8⁺ T cell response in the acute phase is sufficient for parasite control and cannot be further increased by targeting co-inhibitory receptors. In contrast, persistent long-term chronic infection leads to an increase of exhausted T cells within the tissues of persistence. To our knowledge, this is the first description of infection-induced CD8⁺ T cells with an exhausted phenotype and reduced cytokine production in muscles of T. cruzi-infected mice.

Behavioral and Neuropathological Changes After Toxoplasma gondii Ocular Conjunctival Infection in BALB/c Mice

Ocular infection with Toxoplasma gondii causes toxoplasmosis in mice. However, following ocular infection with tachyzoites, the cause of the accompanying progressive changes in hippocampal-dependent tasks, and their relationship with the morphology and number of microglia, is less well understood. Here, in 6-month-old, female BALB/c mice, 5 μl of a suspension containing 48.5 × 10⁶ tachyzoites/ml was introduced into the conjunctival sac; control received an equal volume of saline. Before and after instillation, all mice were subject to an olfactory discrimination (OD) test, using predator (cat) feces, and to an open-field (OF) task. After the behavioral tests, the animals were culled at either 22 or 44 days post-instillation (dpi), and the brains and retinas were dissected and processed for immunohistochemistry. The total number of Iba-1-immunolabeled microglia in the molecular layer of the dentate gyrus was estimated, and three-dimensional reconstructions of the cells were evaluated. Immobility was increased in the infected group at 12, 22, and 43 dpi, but the greatest immobility was observed at 22 dpi and was associated with reduced line crossing in the OF and distance traveled. In the OD test, infected animals spent more time in the compartment with feline fecal material at 14 and at 43 dpi. No OD changes were observed in the control group. The number of microglia was increased at 22 dpi but returned to control levels by 44 dpi. These changes were associated with the differentiation of T. gondii tachyzoites into bradyzoite-enclosed cysts within the brain and retina. Thus, infection of mice with T. gondii alters exploratory behavior, gives rise to a loss in predator’s odor avoidance from 2 weeks after infection, increased microglia number, and altered their morphology in the molecular layer of the dentate gyrus.

Using RVFV as a Vector Platform for the Expression of Ruminant Disease Antigens

Live attenuated viruses remain as vaccine agents with unparalleled performance in terms of duration, magnitude, and breadth of induced immune responses. As the yellow fever-attenuated vaccine strain Y17D, attenuated Rift Valley fever virus shares features suitable to be used as a viral vector for heterologous antigen expression and bivalent vaccine development. Current reverse genetics technology showed the successful rescue of RVFV carrying foreign antigens with little immunogenicity loss in experimental animal models. We show here the basic experimental protocol to achieve the expression of candidate vaccine antigens from other important diseases of ruminants using RVFV as a vector platform as well as preliminary steps for the characterization of immunogenicity in vivo.

Seroprevalence Estimates of Latent and Acute Toxoplasma Infections in HIV+ People-Call for Action in Underprivileged Communities

We undertook a comprehensive, systematic review of observational studies to estimate respective seroprevalences of latent and acute Toxoplasma gondii infections in HIV⁺ people at the global, regional and country levels; related seroprevalence to socio-economic variables and CD4+ cell counts; and assessed temporal changes in prevalence and risk factors for this group. We systematically searched international databases for seroepidemiological surveys between 1 January 1980 and 31 July 2020. We used a random effects model to calculate pooled seroprevalences with 95% confidence intervals (CI), and estimated the numbers of HIV⁺ people inferred to harbour latent and acute T. gondii infections (LT or AT). We grouped seroprevalence data according to the geographic regions defined by the World Health Organization (WHO) and conducted subgroup and meta-regression analyses of the data. Of a total of 4024 studies identified, 150 and 65 of them met the inclusion criteria for LT and AT in HIV⁺ people, respectively. The overall, pooled seroprevalences of LT and AT were 37.4% (95% CI, 33.4–41.4) and 1.3% (95% CI, 0.9–1.8%), equating to ~14.2 and 0.5 million HIV⁺ people, respectively. Most HIV⁺ people with T. gondii infections originated from Africa, and the highest seroprevalences were in low-income countries with low human development indices. Significant risk factors for toxoplasmosis in HIV⁺ patients included the consumption of raw/undercooked meat, frequent contact with soil, a low CD4+ T lymphocyte number (<200 cells per μL) and age. Overall, the finding of high seroprevalences of particularly latent T. gondii infection in HIV⁺ people in underprivileged regions of the world, such as parts of Africa, calls for preventative action. Programs that include routine serological monitoring, counselling, care, animal control and/or prophylactic treatment measures are needed to prevent severe toxoplasmosis from developing in people living with HIV infection. Our study highlights the potential importance of parasite chemoprophylaxis in resource-poor settings, particularly in low-income countries.

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

BACKGROUND

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.

METHOD

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.

RESULTS

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.

CONCLUSION

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.

The Immunoproteasome Subunits LMP2, LMP7 and MECL-1 Are Crucial Along the Induction of Cerebral Toxoplasmosis

Cell survival and function critically relies on the fine-tuned balance of protein synthesis and degradation. In the steady state, the standard proteasome is sufficient to maintain this proteostasis. However, upon inflammation, the sharp increase in protein production requires additional mechanisms to limit protein-associated cellular stress. Under inflammatory conditions and the release of interferons, the immunoproteasome (IP) is induced to support protein processing and recycling. In antigen-presenting cells constitutively expressing IPs, inflammation-related mechanisms contribute to the formation of MHC class I/II-peptide complexes, which are required for the induction of T cell responses. The control of Toxoplasma gondii infection relies on Interferon-γ (IFNγ)-related T cell responses. Whether and how the IP affects the course of anti-parasitic T cell responses along the infection as well as inflammation of the central nervous system is still unknown. To answer this question we used triple knockout (TKO) mice lacking the 3 catalytic subunits of the immunoproteasome (β1i/LMP2, β2i/MECL-1 and β5i/LMP7). Here we show that the numbers of dendritic cells, monocytes and CD8⁺ T cells were reduced in Toxoplasma gondii-infected TKO mice. Furthermore, impaired IFNγ, TNF and iNOS production was accompanied by dysregulated chemokine expression and altered immune cell recruitment to the brain. T cell differentiation was altered, apoptosis rates of microglia and monocytes were elevated and STAT3 downstream signaling was diminished. Consequently, anti-parasitic immune responses were impaired in TKO mice leading to elevated T. gondii burden and prolonged neuroinflammation. In summary we provide evidence for a critical role of the IP subunits β1i/LMP2, β2i/MECL-1 and β5i/LMP7 for the control of cerebral Toxoplasma gondii infection and subsequent neuroinflammation.

Targeted Transcriptomic Analysis of C57BL/6 and BALB/c Mice During Progressive Chronic Toxoplasma gondii Infection Reveals Changes in Host and Parasite Gene Expression Relating to Neuropathology and Resolution

Toxoplasma gondii is a resilient parasite that infects a multitude of warm-blooded hosts and results in a lifelong chronic infection requiring continuous responses by the host. Chronic infection is characterized by a balanced immune response and neuropathology that are driven by changes in gene expression. Previous research pertaining to these processes has been conducted in various mouse models, and much knowledge of infection-induced gene expression changes has been acquired through the use of high throughput sequencing techniques in different mouse strains and post-mortem human studies. However, lack of infection time course data poses a prominent missing link in the understanding of chronic infection, and there is still much that is unknown regarding changes in genes specifically relating to neuropathology and resulting repair mechanisms as infection progresses throughout the different stages of chronicity. In this paper, we present a targeted approach to gene expression analysis during T. gondii infection through the use of NanoString nCounter gene expression assays. Wild type C57BL/6 and BALB/c background mice were infected, and transcriptional changes in the brain were evaluated at 14, 28, and 56 days post infection. Results demonstrate a dramatic shift in both previously demonstrated and novel gene expression relating to neuropathology and resolution in C57BL/6 mice. In addition, comparison between BALB/c and C57BL/6 mice demonstrate initial differences in gene expression that evolve over the course of infection and indicate decreased neuropathology and enhanced repair in BALB/c mice. In conclusion, these studies provide a targeted approach to gene expression analysis in the brain during infection and provide elaboration on previously identified transcriptional changes and also offer insights into further understanding the complexities of chronic T. gondii infection.

Pathophysiology of ocular toxoplasmosis: Facts and open questions

Infections with the protozoan parasite Toxoplasma gondii are frequent, but one of its main consequences, ocular toxoplasmosis (OT), remains poorly understood. While its clinical description has recently attracted more attention and publications, the underlying pathophysiological mechanisms are only sparsely elucidated, which is partly due to the inherent difficulties to establish relevant animal models. Furthermore, the particularities of the ocular environment explain why the abundant knowledge on systemic toxoplasmosis cannot be just transferred to the ocular situation. However, studies undertaken in mouse models have revealed a central role of interferon gamma (IFNγ) and, more surprisingly, interleukin 17 (IL17), in ocular pathology and parasite control. These studies also show the importance of the genetic background of the infective Toxoplasma strain. Indeed, infections due to exotic strains show a completely different pathophysiology, which translates in a different clinical outcome. These elements should lead to more individualized therapy. Furthermore, the recent advance in understanding the immune response during OT paved the way to new research leads, involving immune pathways poorly studied in this particular setting, such as type I and type III interferons. In any case, deeper knowledge of the mechanisms of this pathology is needed to establish new, more targeted treatment schemes.

Humoral and Cell-Mediated Immune Response Validation in Calves after a Live Attenuated Vaccine of Babesia bigemina

The current vaccines to control bovine Babesia bigemina (B. bigemina) infection are not fully protective and vaccination failures incur heavy losses to the cattle industry around the world. Using modified micro-aerophilous stationary phase, we developed a culture-derived attenuated live vaccine against B. bigemina and tested a single subcutaneous inoculation of 2 × 10⁸ infected erythrocytes in calves. The protection was measured after a lethal intravenous challenge with 5 × 10⁸ virulent calf-derived B. bigemina. Our results demonstrated that a single shot of attenuated vaccine was capable of inducing robust humoral and cell-mediated immune responses in calves. We found a significant increase in the IgG antibody titers post-challenge and a strong proliferation of both CD4+ and CD8+ T cells contributing towards the protection. Our vaccine provided complete protection and parasitic clearance, which was followed for more than 100 days post-challenge. This immunity against babesiosis was directly linked to strong humoral responses; however, the parasitic clearance was attributed to significant T cells effector responses in vaccinated calves as compared to the infected control calves. We anticipate that these results will be helpful in the development of more efficient culture-derived vaccines against Babesia infections, thus reducing significant global economic losses to farmers and the cattle industry.

Protective immunity induced by CpG ODN-adjuvanted virus-like particles containing Toxoplasma gondii proteins

AIMS

To date, a Toxoplasma gondii vaccine for clinical use remains unavailable, though multiple vaccine candidates have been suggested. In our previous studies, unadjuvanted virus-like particles (VLPs) vaccines expressing multiple T. gondii antigens were confirmed to be protective against T. gondii challenge infection. Yet, the protective efficacy of adjuvanted T. gondii VLP in comparison with the unadjuvanted counterpart requires elucidation.

METHODS AND RESULTS

In the present study, mice were immunized with the multi-antigenic VLP vaccines (TG146 VLP) with or without CpG adjuvants and their protective efficacies were compared. CpG-adjuvanted TG146 VLP vaccine elicited enhanced T gondii-specific IgG and IgA antibody responses in the sera, mucosal tissue and the brain compared to unadjuvanted VLPs vaccine. Inclusion of CpG adjuvant in vaccines also induced greater CD4⁺ and CD8⁺ T-cell responses, as well as B cell and germinal centre B cell responses from splenocytes and mesenteric lymph nodes. Pro-inflammatory cytokine response and cyst counts in the brain were drastically diminished in mice immunized with CpG-adjuvanted VLP vaccines.

CONCLUSION

Our results demonstrated that CpG-adjuvanted T. gondii VLPs can significantly enhance the protective efficacy of vaccines against T. gondii infection.

IL-21 in Homeostasis of Resident Memory and Exhausted CD8 T Cells during Persistent Infection

CD4 T cells guide the development of CD8 T cells into memory by elaborating mitogenic and differentiation factors and by licensing professional antigen-presenting cells. CD4 T cells also act to stave off CD8 T cell dysfunction during repetitive antigen stimulation in persistent infection and cancer by mitigating generation of exhausted T cells (T_EX). CD4 T cell help is also required for establishing and maintaining tissue-resident memory T cells (T_RM), the nonrecirculating memory T cell subset parked in nonlymphoid tissues to provide frontline defense against reinvading pathogens. Interleukin (IL)-21 is the signature cytokine secreted by follicular helper CD4 T cells (T_FH) to drive B cell expansion and differentiation in germinal centers to mount high-affinity, isotype class-switched antibodies. In several infection models, IL-21 has been identified as the CD4 T help needed for formation and survival of T_RM and T_EX. In this review, we will explore the different memory subsets of CD8 T cells in persistent infections, the metabolic profiles associated with each, and evidence documenting the importance of CD4 T cell-derived IL-21 in regulating CD8 T_RM and T_EX development, homeostasis, and function.

Diagnostic significance of C-reactive protein and hematological parameters in acute toxoplasmosis

Abstract

Toxoplasmosis is a zoonosis caused by Toxoplasma gondii, which can be acquired by oral contact and may cause severe health problems especially for pregnant (congenital toxoplasmosis) and immunocompromised patients. This study aimed to verify the diagnostic significance of hematological parameters and C-reactive protein (CRP) for toxoplasmosis acute detection. A case-control study was carried out between December 2017 and May 2018, in samples of convenience independent of age and sex. The case group was formed by 25 patients with positive anti-Toxoplasma gondii IgG/IgM antibody and the control group was formed by 21 patients with non-positive anti-Toxoplasma gondii IgG/IgM antibody. The results of the hematological parameters and CRP were analyzed in these patients. The patients with Toxoplasma gondii IgM antibody reagent showed higher lymphocytes counting and lower neutrophils counting than the control group. C-reactive protein levels were not different between the groups case and control. ROC curve analysis highlighted that the cut-off value of > 32.00% for lymphocytes and < 57.50% for neutrophils were able to produce specificity higher than 90% for IgM antibody detection. The Naïve Bayes classifier was considered suitable (AUC ≈ 0.700) to separate both groups according to their white cell counting. Changes in lymphocytes and neutrophils may be useful parameters for toxoplasmosis identification and may be used as a tool in the complementary diagnosis of toxoplasmosis.

Graphic abstract

The IL-33/ST2 Axis in Immune Responses Against Parasitic Disease: Potential Therapeutic Applications

Parasitic infections pose a wide and varying threat globally, impacting over 25% of the global population with many more at risk of infection. These infections are comprised of, but not limited to, toxoplasmosis, malaria, leishmaniasis and any one of a wide variety of helminthic infections. While a great deal is understood about the adaptive immune response to each of these parasites, there remains a need to further elucidate the early innate immune response. Interleukin-33 is being revealed as one of the earliest players in the cytokine milieu responding to parasitic invasion, and as such has been given the name "alarmin." A nuclear cytokine, interleukin-33 is housed primarily within epithelial and fibroblastic tissues and is released upon cellular damage or death. Evidence has shown that interleukin-33 seems to play a crucial role in priming the immune system toward a strong T helper type 2 immune response, necessary in the clearance of some parasites, while disease exacerbating in the context of others. With the possibility of being a double-edged sword, a great deal remains to be seen in how interleukin-33 and its receptor ST2 are involved in the immune response different parasites elicit, and how those parasites may manipulate or evade this host mechanism. In this review article we compile the current cutting-edge research into the interleukin-33 response to toxoplasmosis, malaria, leishmania, and helminthic infection. Furthermore, we provide insight into directions interleukin-33 research may take in the future, potential immunotherapeutic applications of interleukin-33 modulation and how a better clarity of early innate immune system responses involving interleukin-33/ST2 signaling may be applied in development of much needed treatment options against parasitic invaders.

Vaccination with gamma radiation-attenuated Toxoplasma gondii protects against ovarian infiltration in mice-bearing Ehrlich ascites carcinoma

Purpose: Cancer is one of the most common causes of mortality and morbidity worldwide. Vaccines have been emerged as an attractive approach for their capacity of eliciting long-term immune response targeting cancer cells. Attenuated avirulent Toxoplasma gondii stimulate immunity and activate antitumor cells thereby eliciting rejection of some established cancer. The purpose of this study was to evaluate the antitumor-protective capacity of vaccination with gamma radiation-attenuated T. gondii against ovarian penetration in Ehrlich ascites carcinoma (EAC)-bearing mice.Materials and methods: Forty-five mice were randomly divided into three groups as follows: nontumor-bearing (normal control); EAC-bearing group (EAC); and mice vaccinated orally with gamma radiation-attenuated T. gondii then inoculated 2 weeks later with EAC (TG + EAC). Survival rate, serum interleukin-12 (IL-12), and levels of IFN-γ mRNA, CD4, and CD8 in ovarian tissues homogenate were assessed. Also, ovarian histopathology and immunohistochemical expressions of metalloproteinase-2, CD34, and vimentin were determined.Results: The group vaccinated with attenuated T. gondii showed significantly increased survival rates, serum IL-12, and levels of IFN-γ, CD4, and CD8 in ovarian tissue homogenates as well as an enhancement of histopathological and immunohistochemical changes compared to EAC-bearing group.Conclusion: Vaccination with gamma radiation-attenuated T. gondii has the capacity to supply immunoprotective impact against ovarian invasion in EAC-bearing mice.