White Adipose Tissue Is a Reservoir for Memory T Cells and Promotes Protective Memory Responses to Infection.

White adipose tissue bridges body organs and plays a fundamental role in host metabolism. To what extent adipose tissue also contributes to immune surveillance and long-term protective defense remains largely unknown. Here, we have shown that at steady state, white adipose tissue contained abundant memory lymphocyte populations. After infection, white adipose tissue accumulated large numbers of pathogen-specific memory T cells, including tissue-resident cells. Memory T cells in white adipose tissue expressed a distinct metabolic profile, and white adipose tissue from previously infected mice was sufficient to protect uninfected mice from lethal pathogen challenge. Induction of recall responses within white adipose tissue was associated with the collapse of lipid metabolism in favor of antimicrobial responses. Our results suggest that white adipose tissue represents a memory T cell reservoir that provides potent and rapid effector memory responses, positioning this compartment as a potential major contributor to immunological memory.

A role for T-cell exhaustion in Long COVID-19 and severe outcomes for several categories of COVID-19 patients.

Unusual mortality rate differences and symptoms have been experienced by COVID-19 patients, and the postinfection symptoms called Long COVID-19 have also been widely experienced. A substantial percentage of COVID-19-infected individuals in specific health categories have been virtually asymptomatic, several other individuals in the same health categories have exhibited several unusual symptoms, and yet other individuals in the same health categories have fatal outcomes. It is now hypothesized that these differences in mortality rates and symptoms could be caused by a SARS-CoV-2 virus infection acting together with one or more latent pathogen infections in certain patients, through mutually beneficial induced immune cell dysfunctions, including T-cell exhaustion. A latent pathogen infection likely to be involved is the protozoan parasite Toxoplasma gondii, which infects approximately one third of the global human population. Furthermore, certain infections and cancers that cause T-cell exhaustion can also explain the more severe outcomes of other COVID-19 patients having several disease and cancer comorbidities.

Human impact on the diversity and virulence of the ubiquitous zoonotic parasite Toxoplasma gondii.

A majority of emerging infectious diseases in humans are zoonoses. Understanding factors that influence the emergence and transmission of zoonoses is pivotal for their prevention and control. Toxoplasma gondii is one of the most widespread zoonotic pathogens known today. Whereas only a few genotypes of T. gondii dominate in the Northern Hemisphere, many genotypes coexist in South America. Furthermore, T. gondii strains from South America are more likely to be virulent than those from the Northern Hemisphere. However, it is not clear what factor(s) shaped modern-day genetic diversity and virulence of T. gondii Here, our analysis suggests that the rise and expansion of farming in the past 11,000 years established the domestic cat/mouse transmission cycle for T. gondii, which has undoubtedly played a significant role in the selection of certain linages of T. gondii Our mathematical simulations showed that within the domestic transmission cycle, intermediately mouse-virulent T. gondii genotypes have an adaptive advantage and eventually become dominant due to a balance between lower host mortality and the ability to superinfect mice previously infected with a less virulent T. gondii strain. Our analysis of the global type II lineage of T. gondii suggests its Old World origin but recent expansion in North America, which is likely the consequence of global human migration and trading. These results have significant implications concerning transmission and evolution of zoonotic pathogens in the rapidly expanding anthropized environment demanded by rapid growth of the human population and intensive international trading at present and in the future.

Metacytofilin Is a Potent Therapeutic Drug Candidate for Toxoplasmosis.

BACKGROUND: Toxoplasmosis, a parasitic disease caused by Toxoplasma gondii, is an important cause of miscarriage or adverse fetal effects, including neurological and ocular manifestations in humans. Current anti-Toxoplasma drugs have limited efficacy against toxoplasmosis and also have severe side effects. Therefore, novel efficacious drugs are urgently needed. Here, we identified metacytofilin (MCF) from a fungal Metarhizium species as a potential anti-Toxoplasma compound. METHODS: Anti-Toxoplasma activities of MCF and its derivatives were evaluated in vitro and in vivo using nonpregnant and pregnant mice. To understand the mode of action of MCF, the RNA expression of host and parasite genes was investigated by RNAseq. RESULTS: In vitro, MCF inhibited the viability of intracellular and extracellular T. gondii. Administering MCF intraperitoneally or orally to mice after infection with T. gondii tachyzoites increased mouse survival compared with the untreated animals. Remarkably, oral administration of MCF to pregnant mice prevented vertical transmission of the parasite. Interestingly, RNA sequencing of T. gondii-infected cells treated with MCF showed that MCF inhibited DNA replication and enhanced RNA degradation in the parasites. CONCLUSIONS: With its potent anti-T. gondii activity, MCF is a strong candidate for future drug development against toxoplasmosis.

The GRA15 protein from Toxoplasma gondii enhances host defense responses by activating the interferon stimulator STING.

Toxoplasma gondii is an important neurotropic pathogen that establishes latent infections in humans that can cause toxoplasmosis in immunocompromised individuals. It replicates inside host cells and has developed several strategies to manipulate host immune responses. However, the cytoplasmic pathogen-sensing pathway that detects T. gondii is not well-characterized. Here, we found that cyclic GMP-AMP synthase (cGAS), a sensor of foreign dsDNA, is required for activation of anti-T. gondii immune signaling in a mouse model. We also found that mice deficient in STING (Stinggt/gt mice) are much more susceptible to T. gondii infection than WT mice. Of note, the induction of inflammatory cytokines, type I IFNs, and interferon-stimulated genes in the spleen from Stinggt/gt mice was significantly impaired. Stinggt/gt mice exhibited more severe symptoms than cGAS-deficient mice after T. gondii infection. Interestingly, we found that the dense granule protein GRA15 from T. gondii is secreted into the host cell cytoplasm and then localizes to the endoplasmic reticulum, mediated by the second transmembrane motif in GRA15, which is essential for activating STING and innate immune responses. Mechanistically, GRA15 promoted STING polyubiquitination at Lys-337 and STING oligomerization in a TRAF protein-dependent manner. Accordingly, GRA15-deficient T. gondii failed to elicit robust innate immune responses compared with WT T. gondii. Consequently, GRA15-/-T. gondii was more virulent and caused higher mortality of WT mice but not Stinggt/gt mice upon infection. Together, T. gondii infection triggers cGAS/STING signaling, which is enhanced by GRA15 in a STING- and TRAF-dependent manner.

Toxoplasmosis as an Early Complication of Allogeneic Hematopoietic Cell Transplantation.

Among 419 consecutive allogeneic hematopoietic cell transplant recipients, we observed 17 (4.0%) cases of toxoplasmosis at a median time of day 45 (range, 6 to 322) after transplant. Seven of these 17 cases occurred before day 30 after transplant. Because of the lack of PCR screening and trimethoprim-sulfamethoxazole prophylaxis before engraftment, the diagnosis of toxoplasmosis was late, and 5 of these 7 patients died. Analyzing these cases, early Toxoplasma blood PCR screening, starting from transplant, is crucial.

Propranolol efficacy as a novel adjuvant for immunization against Toxoplasma gondii tachyzoites.

Severe or lethal damages, caused by Toxoplasma gondii infection in congenital cases and immunocompromised patients implies the necessity for development of a vaccine and an appropriate adjuvant would be needed to elicit a protective Th1 biased-immune response. The adjuvant activity of propranolol was surveyed and compared with alum by immunization of BALB/c mice with protein components of T. gondii tachyzoites. Five groups of BALB/c mice were immunized with phosphate buffered saline (negative control), Toxoplasma lysate antigen (TLA), alum plus TLA, Propranolol plus TLA, and alum, propranolol and TLA. Immunization efficacy was evaluated by lymphocyte proliferation and DTH tests, challenge with live tachyzoites, IFN-γ production by spleen cells, serum TNF-α concentration and anti- Toxoplasma total IgG, IgG1 and IgG2a measurements. Mice of the PRP-TLA group induced significantly more IFN-γ and TNF-α production and lymphocyte proliferation than other groups. This group of mice also showed more anti-T. gondii IgG2a and DTH responses and showed a significantly increased survival time after challenge. These findings indicate that propranolol as an adjuvant in combination with TLA, may enhance cellular immunity against T. gondii.

Effects of Aloe vera and Eucalyptus methanolic extracts on experimental toxoplasmosis in vitro and in vivo.

Toxoplasmosis is a worldwide disease caused by the protozoan parasite Toxoplasma gondii (T. gondii), which is most commonly treated by pyrimethamine and sulfadiazine. However, this treatment presents several adverse side effects; Thus, new drugs with lower toxicities are urgently needed. In this study the anti-T. gondii activity of A. vera and Eucalyptus extracts were evaluated in vitro using a MTT (3-(4, 5-dimethylthiazol-2-yl) 2, 5-diphenyltetrazolium bromide) assay and in vivo by measuring the survival rates of mice infected with 2 × 103 tachyzoites of RH strain of T. gondii and then injected intraperitoneally by different concentrations of extracts for 4 days. Biochemical parameters such as Ferric Reducing Antioxidant Potential (FRAP) and malondialdehyde (MDA) assay were also evaluated. As results, in the in vitro assay, the IC50 values were 13.2, 24.7, 2.63 µg/ml, and the selectivity indexes were 3.3, 2.4, 3.03 for the A. vera, Eucalyptus and pyrimethamine, respectively. The mice treated with Eucalyptus showed a better survival rate than others (P < 0.05). The increased weight of liver and spleen, due to infection, was reduced by treatments. In FRAP assay Eucalyptus showed a better antioxidant activity than the other extracts. MDA levels in both liver and spleen were reduced by treatment. The results show that A. Vera and Eucalyptus possess anti-T. gondii activities in vitro and in vivo, in addition, Eucalyptus shows antioxidant activity with a higher survival rate. Therefore, Eucalyptus may be a useful candidate for treating Toxoplasma infection. Moreover, further studies are required to investigate the fractionations of this plant against T. gondii.

Implementation of Molecular Surveillance After a Cluster of Fatal Toxoplasmosis at 2 Neighboring Transplant Centers.

After a cluster of fatal toxoplasmosis among stem cell transplant recipients at 2 hospitals, surveillance with polymerase chain reaction (PCR) (blood) was instituted. Rate of reactivation among seropositive recipients was 2.2 and 16%. Parasitemia was successfully managed with preemptive treatment. For seropositive recipients unable to take prophylaxis, toxoplasma PCR surveillance should be routinely performed.

Genotyping of Toxoplasma gondii: DNA extraction from formalin-fixed paraffin-embedded autopsy tissues from AIDS patients who died by severe disseminated toxoplasmosis.

This study investigated the genetic features of Toxoplasma gondii isolated directly in autopsies of HIV-infected patients who died with severe disseminated toxoplasmosis. This retrospective analysis was conducted in a cohort of 15 HIV-infected patients with clinical and laboratory data. They had previous cerebral toxoplasmosis at least 6 months before the disseminated toxoplasmosis episode. The hypothesis was that they were infected with highly virulent parasites due to the condition in which they died. T. gondii genotyping was done directly in DNA extracted from 30 autopsy brain and lung samples (2 per patient) and mutilocus PCR-RFLP genotyping was done using 12 molecular markers. The 30 clinical samples were genotyped successfully in 8 or more loci and six suggestive genotypes were identified. One of them was Toxo DB #11, previously identified in different domestic animals and virulent in experimental animals. The other five suggestive genotypes identified in 14 patients were not described. TgHuDis1 was the most frequent and was determined in 8 patients. TgHuDis3 and TgHuDis5 were identified in two patients each. TgHuDis2 and TgHuDis4 have been identified in one patient each. These suggestive genotypes could be considered as virulent, since they caused severe tissue damage and had similar characteristics as Toxo # DB 11.

Co-administration of interleukins 7 and 15 with DNA vaccine improves protective immunity against Toxoplasma gondii.

Toxoplasma gondii is an obligatory intracellular parasite, which can infect all warm-blooded animals including humans. Cytokines, including IL-15 and IL-7, play a critical role in the regulation of the homeostasis of naive and memory T cells. Co-administration the DNA vaccine with cytokines may improve its efficacy. IL-7 and IL-15 from splenic tissues of Kunming mice were cloned, and eukaryotic plasmid pVAX-IL-7-IL-15 was constructed. Kunming mice were administrated with DNA vaccine expressing T. gondii calcium-dependent protein kinase 1 (TgCDPK1), pVAX-CDPK1, in the presence or absence of IL-7 and IL-15 plasmids (pVAX-IL-7-IL-15), immune responses were analyzed including lymphoproliferative assay, cytokine and serum antibody measurements, flow cytometric surface markers on lymphocytes, and thus protective immunity against acute and chronic T. gondii infection was estimated. Mice injected with pVAX-CDPK1 supplemented with pVAX-IL-7-IL-15 showed higher Toxoplasma-specific IgG2a titers, Th1 responses associated with the production of IFN-γ, IL-2 as well as cell-mediated cytotoxic activity where stronger frequencies of IFN-γ secreting CD8+ and CD4+ T cells (CD8+/CD4+ IFN-γ+ T cells) compared to controls. Co-administration of pVAX-IL-7-IL-15 and pVAX-CDPK1 significantly (P < 0.05) increased survival time (18.07 ± 5.43 days) compared with pVAX-CDPK1 (14.13 ± 3.85 days) or pVAX-IL-7-IL-15 (11.73 ± 1.83 days) alone, and pVAX-IL-7-IL-15 + pVAX-CDPK1 significantly reduced the number of brain cysts (73.5%) in contrast to pVAX-CDPK1 (46.0%) or pVAX-IL-7-IL-15 alone (45.0%). Our results indicate that supplementation of DNA vaccine with IL-7 and IL-15 would facilitate specific humoral and cellular immune responses elicited by DNA vaccine against acute and chronic T. gondii infection in mice.

Deletion of mitogen-activated protein kinase 1 inhibits development and growth of Toxoplasma gondii.

Mitogen-activated protein kinases (MAPKs) regulate key signaling events in a variety of eukaryotic cells. Toxoplasma gondii, the causative agents of toxoplasmosis, possesses a p38α MAPK homologue, MAPK1, which is an important manipulator of host immunity and virulence in mice. In this work, we showed an increased transcript level of MAPK1 in T. gondii during bradyzoite differentiation induced by alkaline treatment and heat shock in vitro, suggesting that MAPK1 may be associated with bradyzoite differentiation. The biological roles of MAPK1 of T. gondii were investigated by construction of a MAPK1 deletion mutant (Δmapk1) and a complementation mutant with restored MAPK1 expression using a type I strain. Knockout of MAPK1 resulted in markedly defective bradyzoite differentiation, host-cell attachment and parasite replication in vitro, and the inability to cause lethal infection in a murine model of acute toxoplasmosis, with lower parasite burden in infected tissues, showing that MAPK1 is associated with the acute virulence of parasite in mice. Complementation of MAPK1-deficient parasites restored bradyzoite development, attachment, replication, and virulence. Our findings demonstrate that MAPK1 is involved in asexual development and growth of T. gondii.

Four cases of fatal toxoplasmosis in three species of endemic New Zealand birds.

Four cases of fatal toxoplasmosis in three endemic New Zealand avian species are reported. Between 2009 and 2012, two kereru (Hemiphaga novaeseelandiae), one North Island brown kiwi (Apteryx mantelli), and one North Island kaka (Nestor meridionalis) were submitted for necropsy examination. On gross postmortem, the kiwi had marked hepatosplenomegaly while the kaka and two kereru had swollen, slightly firm, deep-red lungs. Histologically there was extensive hepatocellular necrosis in the liver of the kiwi while the kaka and kereru showed severe fibrinous bronchointerstitial pneumonia. In the kiwi, protozoal organisms were present within both hepatocytes and Kupffer cells of the liver and within the epithelial cells and macrophages of the interstitium of the lungs in the kaka and two kereru. The diagnosis of toxoplasmosis was confirmed with immunohistochemistry and PCR of paraffin-embedded formalin-fixed tissue of the liver, lungs, or both. Genotyping of up to seven markers revealed that an atypical Type II isolate of Toxoplasma gondii was present in at least three of the cases. This study provides evidence that T. gondii can cause mortality in these endemic species and suggests further research is needed to determine the full extent of morbidity and mortality caused by this parasite in New Zealand's unique avifauna.

Heligmosomoides bakeri and Toxoplasma gondii co-infection leads to increased mortality associated with changes in immune resistance in the lymphoid compartment and disease pathology.

Co-infections are a common reality but understanding how the immune system responds in this context is complex and can be unpredictable. Heligmosomoides bakeri (parasitic roundworm, previously Heligmosomoides polygyrus) and Toxoplasma gondii (protozoan parasite) are well studied organisms that stimulate a characteristic Th2 and Th1 response, respectively. Several studies have demonstrated reduced inflammatory cytokine responses in animals co-infected with such organisms. However, while general cytokine signatures have been examined, the impact of the different cytokine producing lymphocytes on parasite control/clearance is not fully understood. We investigated five different lymphocyte populations (NK, NKT, γδ T, CD4+ T and CD8+ T cells), five organs (small intestine, Peyer's patches, mesenteric lymph nodes, spleen and liver), and 4 cytokines (IFN©, IL-4, IL-10 and IL-13) at two different time points (days 5 and 10 post T. gondii infection). We found that co-infected animals had significantly higher mortality than either single infection. This was accompanied by transient and local changes in parasite loads and cytokine profiles. Despite the early changes in lymphocyte and cytokine profiles, severe intestinal pathology in co-infected mice likely contributed to early mortality due to significant damage by both parasites in the small intestine. Our work demonstrates the importance of taking a broad view during infection research, studying multiple cell types, organs/tissues and time points to link and/or uncouple immunological from pathological findings. Our results provide insights into how co-infection with parasites stimulating different arms of the immune system can lead to drastic changes in infection dynamics.

Clinical features and outcomes in patients with disseminated toxoplasmosis admitted to intensive care: a multicenter study.

BACKGROUND: Characteristics and outcomes of adult patients with disseminated toxoplasmosis admitted to the intensive care unit (ICU) have rarely been described. METHODS: We performed a retrospective study on consecutive adult patients with disseminated toxoplasmosis who were admitted from January 2002 through December 2012 to the ICUs of 14 university-affiliated hospitals in France. Disseminated toxoplasmosis was defined as microbiological or histological evidence of disease affecting >1 organ in immunosuppressed patients. Isolated cases of cerebral toxoplasmosis were excluded. Clinical data on admission and risk factors for 60-day mortality were collected. RESULTS: Thirty-eight patients were identified during the study period. Twenty-two (58%) had received an allogeneic hematopoietic stem cell transplant (median, 61 [interquartile range {IQR}, 43-175] days before ICU admission), 4 (10%) were solid organ transplant recipients, and 10 (27%) were infected with human immunodeficiency virus (median CD4 cell count, 14 [IQR, 6-33] cells/µL). The main indications for ICU admission were acute respiratory failure (89%) and shock (53%). The 60-day mortality rate was 82%. Allogeneic hematopoietic stem cell transplant (hazard ratio [HR] = 2.28; 95% confidence interval [CI], 1.05-5.35; P = .04) and systolic cardiac dysfunction (HR = 3.54; 95% CI, 1.60-8.10; P < .01) within 48 hours of ICU admission were associated with mortality. CONCLUSIONS: Severe disseminated toxoplasmosis leading to ICU admission has a poor prognosis. Recipients of allogeneic hematopoietic stem cell transplant appear to have the highest risk of mortality. We identified systolic cardiac dysfunction as a major determinant of outcome. Strategies aimed at preventing this fatal opportunistic infection may improve outcomes.

Association of neurotropic viruses in HIV-infected individuals who died of secondary complications of tuberculosis, cryptococcosis, or toxoplasmosis in South India.

The frequencies of 10 opportunistic DNA viruses were determined by multiplex real-time PCR in paired cerebrospinal fluid (CSF) and brain tissue of HIV-infected individuals. In the CSF, viruses were detectable in 45/55 cases: JC virus (JCV) in 62%, Epstein-Barr virus (EBV) in 44%, cytomegalovirus (CMV) in 25%, varicella-zoster virus (VZV) in 3.6%, herpes simplex virus 1 (HSV-1) in 1.8%, and human herpesvirus 6 (HHV-6) in 1.8% of cases. A single virus was detectable in 20 cases, 19 cases had coinfection with two viruses, and 6 cases were positive for three viruses. JCV was detectable in the CSF of 62% of cases and in 42% of brain tissues, with higher loads in progressive multifocal leukoencephalopathy (PML) (P < 0.05).

Toxoplasmosis in cord blood transplantation recipients.

Toxoplasmosis is a devastating opportunistic infection that can affect immunocompromised patients such as cord blood transplantation (CBT) recipients. The clinical characteristics of 4 toxoplasmosis CBT patients treated at our institution are reviewed, together with 5 cases collected from the literature. The rate of toxoplasmosis in our hospital was 6% in CBT recipients and 0.2% in other types of allogeneic hematopoietic stem cell transplantation (P < 0.001). Five patients (56%) presented disseminated toxoplasmosis and 4 patients (44%) had localized infection in the central nervous system. In 5 of the 9 patients considered (56%), cytomegalovirus viral replication had been detected before the clinical onset of toxoplasmosis. Seven patients (78%) had previously developed graft-versus-host disease. All patients who exhibited disseminated disease died due to Toxoplasma infection. Pre-transplant serology was positive in 1 patient, negative in 3 patients, and not performed in another. Only 1 of these 5 patients with disseminated disease had received Toxoplasma prophylaxis with cotrimoxazole. It could be concluded that mortality in CBT patients with disseminated toxoplasmosis is unacceptably high. The negative results of serology in the majority of these cases, and its unspecific clinical presentation, makes diagnosis exceedingly difficult. Better diagnostic tests and prophylaxis strategy are needed in CBT recipients.

Oral oocyst-induced mouse model of toxoplasmosis: effect of infection with Toxoplasma gondii strains of different genotypes, dose, and mouse strains (transgenic, out-bred, in-bred) on pathogenesis and mortality.

Humans and other hosts acquire Toxoplasma gondii infection by ingesting tissue cysts in undercooked meat, or by food or drink contaminated with oocysts. Currently, there is no vaccine to prevent clinical disease due this parasite in humans, although, various T. gondii vaccine candidates are being developed. Mice are generally used to test the protective efficacy of vaccines because they are susceptible, reagents are available to measure immune parameters in mice, and they are easily managed in the laboratory. In the present study, pathogenesis of toxoplasmosis was studied in mice of different strains, including Human Leukocyte Antigen (HLA) transgenic mice infected with different doses of T. gondii strains of different genotypes derived from several countries. Based on many experiments, the decreasing order of infectivity and pathogenicity of oocysts was: C57BL/6 background interferon gamma gene knock out (KO), HLA-A*1101, HLA-A*0201, HLA-B*0702, Swiss Webster, C57/black, and BALB/c. Mice fed as few as 1 oocyst of Type I and several atypical strains died of acute toxoplasmosis within 21 days p.i. Some Type II, and III strains were less virulent. The model developed herein should prove to be extremely useful for testing vaccines because it is possible to accurately quantitate a challenge inoculum, test the response to different strains of T. gondii using the same preparations of oocysts which are stable for up to a year, and to have highly reproducible responses to the infection.

Depletion of CD25⁺ cells during acute toxoplasmosis does not significantly increase mortality in Swiss OF1 mice.

The interleukin (IL)-2R alpha chain (CD25) is expressed on regulatory T cells (Treg), which constitute more than 85% of the CD25+ T cell population in a naïve mouse. CD25 is also expressed on effector T cells in mice suffering from an acute infection by the obligate intracellular protozoan parasite, Toxoplasma gondii. Lethal toxoplasmosis is accompanied by a significant loss of Treg in mice naturally susceptible to toxoplasmosis. The present study was done to explore the role of Treg cells using an anti-CD25 antibody-mediated depletion in mice naturally resistant to toxoplasmosis. Although a significant decrease in the percentage of Treg cells was observed following anti-CD25 monoclonal antibody injections, the depletion of CD25+ cells during acute toxoplasmosis did not significantly increase the mortality of Swiss OF1 mice and no significant difference was observed in the brain parasitic load between the mice in the depleted-infected and isotype-infected groups. We found no significant difference between the titres of total IgG in the sera of the mice from the two groups in the chronic phase. However, CD25+ cells depletion was followed by significantly higher levels of IL-12 in the serum of depleted mice than in that of mice injected with the isotype control antibody.