Infection with Toxoplasma gondii alters lymphotoxin expression associated with changes in splenic architecture

Effectiveness of Gamma Rays in Attenuation of Toxoplasma gondii Pathogenicity and Eliciting Immune Response in Mice

Gamma irradiation was applied to the tachyzoites Toxoplasma gondii virulent strain at doses of 0.25, 0.5, 1, 1.5 and 2 KGy. Radiation's effects were assessed both in vivo and in vitro. In vitro, the modest dosage of radiation, 0.25 KGy, showed 97% tachyzoites viability with only slight surface abnormalities and a normal crescent form using a scanning electron microscope. Protein analysis by SDS-PAGE demonstrated that while higher doses of radiation altered the protein banding profile, the 0.25 KGy irradiated tachyzoites showed no significant changes compared to the control (non-irradiated tachyzoites). While, tachyzoites exposed to the higher dose of irradiation (1, 1.5 and 2 KGy) resulted in the appearance of a new protein band as the molecular weights detected were 60, 30 and 10 kDa for antigens prepared from tachyzoites exposed to 1 kDa, and 1.5 and 60, 28 kDa for antigen prepared from tachyzoites exposed to 2 KGy. The immunogenicity of the tachyzoites exposed to radiation did not reveal any significant change in comparison with no irradiated tachyzoites when tested by ELISA using sheep-infected sera. A study conducted in vivo evaluated the infectivity of irradiation tachyzoites by inoculating mice with a 2500 tachyzoites virulent strain/mouse. There are six groups of mice, each with twelve animals, for the six doses of radiation. Mice harbouring irradiation tachyzoites remained viable until 40 days post-inoculation. On the other hand, the mice of control group had a mean survival time of 6.5 ± 0.22 days, and none of them survived past 7 dpi. Comparing the attenuated T. gondii tachyzoites at 0.25 KGy to the control group and other groups injected with irradiated tachyzoites, the results showed statistically significant increases in total IgG. Compared to other irradiation groups, the group injected with 0.25 KGy irradiated tachyzoites had a considerably higher level of IFN γ and IL17 (p < 0.000001). The groups which received 0.25 and 0.5 KGy irradiated tachyzoites as an injection showed no discernible variation in their higher levels of IL12. The findings imply that gamma irradiation was successful in reducing the pathogenicity of the T. gondii virulent strain while preserving the potential of the irradiated tachyzoites to induce an immunological reaction. An investigation into this immune response's immunoprotective potential is advised.

Early immune response to Toxoplasma gondii lineage III isolates of different virulence phenotype

Introduction

Toxoplasma gondii is an intracellular parasite of importance to human and veterinary health. The structure and diversity of the genotype population of T. gondii varies considerably with respect to geography, but three lineages, type I, II and III, are distributed globally. Lineage III genotypes are the least well characterized in terms of biology, host immunity and virulence. Once a host is infected with T.gondii, innate immune mechanisms are engaged to reduce the parasite burden in tissues and create a pro-inflammatory environment in which the TH1 response develops to ensure survival. This study investigated the early cellular immune response of Swiss-Webster mice post intraperitoneal infection with 10 tachyzoites of four distinct non-clonal genotypes of lineage III and a local isolate of ToxoDB#1. The virulence phenotype, cumulative mortality (CM) and allele profiles of ROP5, ROP16, ROP18 and GRA15 were published previously.

Methods

Parasite dissemination in different tissues was analyzed by real-time PCR and relative expression levels of IFNγ, IL12-p40, IL-10 and TBX21 in the cervical lymph nodes (CLN), brain and spleen were calculated using the ΔΔCt method. Stage conversion was determined by detection of the BAG1 transcript in the brain.

Results

Tissue dissemination depends on the virulence phenotype but not CM, while the TBX21 and cytokine levels and kinetics correlate better with CM than virulence phenotype. The earliest detection of BAG1 was seven days post infection. Only infection with the genotype of high CM (69.4%) was associated with high T-bet levels in the CLN 24 h and high systemic IFNγ expression which was sustained over the first week, while infection with genotypes of lower CM (38.8%, 10.7% and 6.8%) is characterized by down-regulation and/or low systemic levels of IFNγ. The response intensity, as assessed by cytokine levels, to the genotype of high CM wanes over time, while it increases gradually to genotypes of lower CM.

Discussion

The results point to the conclusion that the immune response is not correlated with the virulence phenotype and/or allele profile, but an early onset, intense pro-inflammatory response is characteristic of genotypes with high CM. Additionally, high IFNγ level in the brain may hamper stage conversion.

Lymphocyte HVEM/BTLA co-expression after critical illness demonstrates severity indiscriminate upregulation, impacting critical illness-induced immunosuppression

Introduction

The co-regulatory molecule, HVEM, can stimulate or inhibit immune function, but when co-expressed with BTLA, forms an inert complex preventing signaling. Altered HVEM or BTLA expression, separately have been associated with increased nosocomial infections in critical illness. Given that severe injury induces immunosuppression, we hypothesized that varying severity of shock and sepsis in murine models and critically ill patients would induce variable increases in HVEM/BTLA leukocyte co-expression.

Methods

In this study, varying severities of murine models of critical illness were utilized to explore HVEM⁺BTLA⁺ co-expression in the thymic and splenic immune compartments, while circulating blood lymphocytes from critically ill patients were also assessed for HVEM⁺BTLA⁺ co-expression.

Results

Higher severity murine models resulted in minimal change in HVEM⁺BTLA⁺ co-expression, while the lower severity model demonstrated increased HVEM⁺BTLA⁺ co-expression on thymic and splenic CD4⁺ lymphocytes and splenic B220⁺ lymphocytes at the 48-hour time point. Patients demonstrated increased co-expression of HVEM⁺BTLA⁺ on CD3⁺ lymphocytes compared to controls, as well as CD3⁺Ki67^- lymphocytes. Both L-CLP 48hr mice and critically ill patients demonstrated significant increases in TNF-α.

Discussion

While HVEM increased on leukocytes after critical illness in mice and patients, changes in co-expression did not relate to degree of injury severity of murine model. Rather, co-expression increases were seen at later time points in lower severity models, suggesting this mechanism evolves temporally. Increased co-expression on CD3⁺ lymphocytes in patients on non-proliferating cells, and associated TNF-α level increases, suggest post-critical illness co-expression does associate with developing immune suppression.

Plasmodium infection disrupts the T follicular helper cell response to heterologous immunization

Naturally acquired immunity to malaria develops only after many years and repeated exposures, raising the question of whether Plasmodium parasites, the etiological agents of malaria, suppress the ability of dendritic cells (DCs) to activate optimal T cell responses. We demonstrated recently that B cells, rather than DCs, are the principal activators of CD4⁺ T cells in murine malaria. In the present study, we further investigated factors that might prevent DCs from priming Plasmodium-specific T helper cell responses. We found that DCs were significantly less efficient at taking up infected red blood cells (iRBCs) compared to soluble antigen, whereas B cells more readily bound iRBCs. To assess whether DCs retained the capacity to present soluble antigen during malaria, we measured responses to a heterologous protein immunization administered to naïve mice or mice infected with P. chabaudi. Antigen uptake, DC activation, and expansion of immunogen-specific T cells were intact in infected mice, indicating DCs remained functional. However, polarization of the immunogen-specific response was dramatically altered, with a near-complete loss of germinal center T follicular helper cells specific for the immunogen, accompanied by significant reductions in antigen-specific B cells and antibody. Our results indicate that DCs remain competent to activate T cells during Plasmodium infection, but that T cell polarization and humoral responses are severely disrupted. This study provides mechanistic insight into the development of both Plasmodium-specific and heterologous adaptive responses in hosts with malaria.

HSC-derived fatty acid oxidation in steady-state and stressed hematopoiesis

Metabolism impacts all cellular functions and plays a fundamental role in physiology. Metabolic regulation of hematopoiesis is dynamically regulated under steady-state and stress conditions. It is clear that hematopoietic stem cells (HSCs) impose different energy demands and flexibility during maintenance compared with stressed conditions. However, the cellular and molecular mechanisms underlying metabolic regulation in HSCs remain poorly understood. In this review, we focus on defining the role of fatty acid oxidation (FAO) in HSCs. We first review the existing literature describing FAO in HSCs under steady-state hematopoiesis. Next, we describe the models used to examine HSCs under stress conditions, and, finally, we describe how infection causes a shift toward FAO in HSCs and the impact of using this pathway on emergency hematopoiesis.

Experimental infection of Mongolian gerbils with Toxoplasma gondii: pathological and immunohistochemical evaluations

Toxoplasma gondii is a protozoon parasite which causes toxoplasmosis both in human and warm-blooded animals. Toxoplasmosis is a worldwide disease and largely threats human and animal health consequently causing economic losses. Also, it affects the visceral organs in different severity degrees according to the strain of parasite and the host. In this study, experimental toxoplasmosis was performed via intra-peritoneal route in 12 gerbils by administrating 5.00 × 10³ tachyzoites of T. gondii RH strain. The gerbils were sacrificed 7 days after inoculation. All systemic organs were obtained via necropsy and examined by immunohistochemical and histopathological methods. Lesions infected with T. gondii mostly observed in the serosa of abdominal cavity organs including stomach, liver, spleen, intestines, and kidneys. The lesions were most severe in liver. The parasite showed an affinity for the hepatic tissue. To our knowledge, this is the first experimental study of acute T. gondii infection in gerbil evaluating macroscopic, microscopic and immunohistochemical findings. It is concluded that Mongolian gerbils can be used as experimental animals to investigate toxoplasmosis. Also, these animals are very suitable hosts to study liver pathology and pathobiology of T. gondii-related hepatitis.

Histopathological, Immunohistochemical and Biochemical Studies of Murine Hepatosplenic Tissues Affected by Chronic Toxoplasmosis

Toxoplasmosis is a serious health problem in humans and animals resulting from obligatory intracellular invasion of reticuloendothelial tissue by Toxoplasma gondii. The profound pathologic effect of toxoplasmosis is confined to nervous tissue, but many other organs, including the liver and spleen, are insulted. Many molecules like caspase-3, CD3, and CD138 are implicated in the tissue immune response in a trial to alleviate hazardous toxoplasmosis impact. This study aimed to investigate the effect of chronic toxoplasmosis on the liver and spleen tissues of mice using biochemical and histopathological techniques and to detect the activity and level of expression of caspase-3, CD3, and CD138 in these tissues using immunohistochemical labeling. Compared with normal control, altered normal histological features accompanied by inflammatory reaction were recorded in hepatosplenic reticuloendothelial tissues in chronically infected mice. The biochemical profile of the liver has been changed in the form of increased liver enzymes, and oxidative stress has been evidenced by elevated nitric oxide (NO) concentration in liver homogenate. The levels of caspase3, CD3, and CD138 were markedly expressed in the liver and spleen of infected mice. Our findings revealed the persistent effect of latent toxoplasmosis on the host's histological architecture, metabolic, and immunological profile, creating a continued challenging host-parasite relationship.

Remarkable histopathological improvement of experimental toxoplasmosis after receiving spiramycin-chitosan nanoparticles formulation

The present study investigated the anti-Toxoplasma effect of chitosan nanoparticles [CS NPs], spiramycin, spiramycin co-administered with metronidazole and spiramycin-CS NPs formulation on the parasite burden and histopathological changes in the liver, spleen and brain in experimentally infected mice. Seventy male Swiss albino mice were classified into seven equal groups: healthy control (I), infected untreated control (II), infected group receiving CS NPs (III), spiramycin administered infected group (IV), infected group receiving spiramycin-metronidazole (V), infected receiving 400 mg/kg spiramycin-CS NPs (VI) and infected treated with spiramycin-loaded CS NPs 100 mg/kg (VII). All groups were inoculated intraperitoneally with 2500 T. gondii tachyzoites RH strain except the healthy control group. All groups were sacrificed on the 8th day after infection. Density of the parasite and histopathological examination of the liver, spleen and brain of all treated mice revealed reduction in the mean tachyzoites count as well as decreased inflammation, congestion and necrosis within tissue sections. Spiramycin-loaded NPs displayed the highest significant reduction in the pathological insult tailed by spiramycin-metronidazole and CS NPs. In conclusion, spiramycin-loaded CS NPs showed a promising synergistic combination in the treatment of the histopathology caused by toxoplasmosis.

Genetic mapping reveals Nfkbid as a central regulator of humoral immunity to Toxoplasma gondii

Protective immunity to parasitic infections has been difficult to elicit by vaccines. Among parasites that evade vaccine-induced immunity is Toxoplasma gondii, which causes lethal secondary infections in chronically infected mice. Here we report that unlike susceptible C57BL/6J mice, A/J mice were highly resistant to secondary infection. To identify correlates of immunity, we utilized forward genetics to identify Nfkbid, a nuclear regulator of NF-κB that is required for B cell activation and B-1 cell development. Nfkbid-null mice (“bumble”) did not generate parasite-specific IgM and lacked robust parasite-specific IgG, which correlated with defects in B-2 cell maturation and class-switch recombination. Though high-affinity antibodies were B-2 derived, transfer of B-1 cells partially rescued the immunity defects observed in bumble mice and were required for 100% vaccine efficacy in bone marrow chimeric mice. Immunity in resistant mice correlated with robust isotype class-switching in both B cell lineages, which can be fine-tuned by Nfkbid gene expression. We propose a model whereby humoral immunity to T. gondii is regulated by Nfkbid and requires B-1 and B-2 cells for full protection.

Eukaryotic parasitic diseases account for approximately one fifth of all childhood deaths, yet no highly protective vaccine exists for any human parasite. More research must be done to discover how to elicit protective vaccine-induced immunity to parasitic pathogens. We used an unbiased genetic screen to find key genes responsible for immunity to the eukaryotic parasite Toxoplasma gondii. Our screen found Nfkbid, a transcription factor regulator, which controls B cell activation and innate-like B-1 cell development. Mice without Nfkbid were not protected against T. gondii and were deficient at making antibodies against the parasite. Our survival studies of vaccinated mice with and without B-1 compartments found that B-1 cells improved survival, suggesting that B-1 cells act in conjunction with B-2 cells to provide vaccine-induced immunity. Nfkbid and other loci identified in our unbiased screen represent potential targets for vaccines to elicit protective immune responses against parasitic pathogens.

Mucosal Administration of Recombinant Baculovirus Displaying Toxoplasma gondii ROP4 Confers Protection Against T. gondii Challenge Infection in Mice

Pathogens require physical contact with the mucosal surface of the host organism to initiate infection and as such, vaccines eliciting both mucosal and systemic immune responses would be promising. Studies involving the use of recombinant baculoviruses (rBVs) as mucosal vaccines are severely lacking despite their inherently safe nature, especially against pathogens of global importance such as Toxoplasma gondii. Here, we generated rBVs displaying T. gondii rhoptry protein 4 (ROP4) and evaluated their protective efficacy in BALB/c mice following immunization via intranasal (IN) and oral routes. IN immunization with the ROP4-expressing rBVs elicited higher levels of parasite-specific IgA antibody responses compared to oral immunization. Upon challenge infection with a lethal dose of T. gondii ME49, IN immunization elicited significantly higher parasite-specific antibody responses in the mucosal tissues such as intestines, feces, vaginal samples, and brain than oral immunization. Marked increases in IgG and IgA antibody-secreting cell (ASC) responses were observed from intranasally immunized mice. IN immunization elicited significantly enhanced induction of CD4+, CD8+ T cells, and germinal center B (GC B) cell responses from secondary lymphoid organs while limiting the production of the inflammatory cytokines IFN-γ and IL-6 in the brain, all of which contributed to protecting mice against T. gondii lethal challenge infection. Our findings suggest that IN delivery of ROP4 rBVs induced better mucosal and systemic immunity against the lethal T. gondii challenge infection compared to oral immunization.

Lymphotoxin β Receptor: a Crucial Role in Innate and Adaptive Immune Responses against Toxoplasma gondii

The lymphotoxin β receptor (LTβR) plays an essential role in the initiation of immune responses to intracellular pathogens. In mice, the LTβR is crucial for surviving acute toxoplasmosis; however, until now, a functional analysis was largely incomplete. Here, we demonstrate that the LTβR is a key regulator required for the intricate balance of adaptive immune responses. Toxoplasma gondii-infected LTβR-deficient (LTβR^−/−) mice show globally altered interferon-γ (IFN-γ) regulation, reduced IFN-γ-controlled host effector molecule expression, impaired T cell functionality, and an absent anti-parasite-specific IgG response, resulting in a severe loss of immune control of the parasites. Reconstitution of LTβR^−/− mice with toxoplasma immune serum significantly prolongs survival following T. gondii infection. Notably, analysis of RNA-seq data clearly indicates a specific effect of T. gondii infection on the B cell response and isotype switching. This study uncovers the decisive role of the LTβR in cytokine regulation and adaptive immune responses to control T. gondii.

The Shaping of a B Cell Pool Maximally Responsive to Infections

B cell subsets differ in development, tissue distribution, and mechanisms of activation. In response to infections, however, all can differentiate into extrafollicular plasmablasts that rapidly provide highly protective antibodies, indicating that these plasmablasts are the main humoral immune response effectors. Yet, the effectiveness of this response type depends on the presence of antigen-specific precursors in the circulating mature B cell pool, a pool that is generated initially through the stochastic processes of B cell receptor assembly. Importantly, germinal centers then mold the repertoire of this B cell pool to be increasingly responsive to pathogens by generating a broad array of antimicrobial memory B cells that act as highly effective precursors of extrafollicular plasmablasts. Such B cell repertoire molding occurs in two ways: continuously via the chronic germinal centers of mucosal lymphoid tissues, driven by the presence of the microbiome, and via de novo generated germinal centers following acute infections. For effectively evaluating humoral immunity as a correlate of immune protection, it might be critical to measure memory B cell pools in addition to antibody titers.

Comparative Characteristics of the Spleen White Pulp in Experimental Models of Sepsis Caused by Different Strains of Pseudomonas aeruginosa

We describe reactive changes in the spleen white pulp in male C57BL/6 mice with experimental sepsis induced by intraperitoneal administration of Pseudomonas aeruginosa 1840 (Pa1840) with exotoxin U gene or Pseudomonas aeruginosa 1623 (Pa1623) with exotoxin S gene. Histological analysis and morphometry revealed hypoplasia of the spleen white pulp in mice with sepsis induced by Pa1840, while sepsis caused by Pa1623 was associated with its hyperplasia; with apoptosis of white pulp cells was observed in both cases. The results attest to ambiguous nature of the reactive changes in the white pulp of the spleen in experimental sepsis models initiated by Pa1840 and Pa1623 stains.

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.

Toxoplasma gondii causes lipofuscinosis, collagenopathy and spleen and white pulp atrophy during the acute phase of infection

In this study, we evaluated homeostatic and functional disorders of the spleen in mice inoculated with Toxoplasma gondii. The kinetics of megakaryocyte and leukocyte production, body and spleen mass and certain histopathological aspects were analyzed. There was increased (P < 0.05) the accumulation of lipofuscin in the red pulp of the spleen, in the periods of 30 and 60 dpi of the infection, that is, in the chronification stage of the disease and decrease of the white pulp area. In addition, we observed (from 7dpi) a quantitative and qualitative increase (P < 0.05) in the deposition of collagen fibers in the spleen of all infected mice. Since resolution of the inflammatory process resulted in pathophysiological changes, we can suggest that the T. gondii invaded and multiplied in the cells of the white and red pulps of the spleen. Although we did not find the parasite in the spleen, this hypothesis is supported by the presence of diffuse inflammatory infiltrate, which extended through the spleen parenchyma of all inoculated mice. Taken together, our results suggest that T. gondii causes severe homeostatic disorders that have altered spleen physiology, including diffuse parenchymal inflammation, lipofuscinosis in histiocytes, early aging, collagenopathy, systemic sclerosis and spleen and white pulp atrophy.

ICOS-deficient and ICOS YF mutant mice fail to control Toxoplasma gondii infection of the brain

Resistance to chronic Toxoplasma gondii infection requires ongoing recruitment of T cells to the brain. Thus, the factors that promote, sustain, and regulate the T cell response to the parasite in the brain are of great interest. The costimulatory molecule ICOS (inducible T cell costimulator) has been reported to act largely through the PI3K pathway in T cells, and can play pro-inflammatory or pro-regulatory roles depending on the inflammatory context and T cell type being studied. During infection with T. gondii, ICOS promotes early T cell responses, while in the chronic stage of infection ICOS plays a regulatory role by limiting T cell responses in the brain. We sought to characterize the role of ICOS signaling through PI3K during chronic infection using two models of ICOS deficiency: total ICOS knockout (KO) mice and ICOS YF mice that are unable to activate PI3K signaling. Overall, ICOS KO and ICOS YF mice had similar severe defects in parasite-specific IgG production and parasite control compared to WT mice. Additionally, we observed expanded effector T cell populations and a loss of Treg frequency in the brains of both ICOS KO and ICOS YF mice. When comparing the remaining Treg populations in infected mice, ICOS KO Tregs expressed WT levels of Foxp3 and CD25, while ICOS YF Tregs expressed significantly less Foxp3 and CD25 compared to both WT and ICOS KO mice. Together, these results suggest that PI3K-independent signaling downstream of ICOS plays an important role in Treg stability in the context of chronic inflammation.

Impact of Interleukin-27p28 on T and B Cell Responses during Toxoplasmosis

Interleukin-27 (IL-27) is a heterodimeric cytokine composed of the subunits IL-27p28 and EBi3, and while the IL-27 heterodimer influences T cell activities, there is evidence that IL-27p28 can have EBi3-independent activities; however, their relevance to infection is unclear. Therefore, the studies presented here compared how IL-27p28 transgenics and IL-27p28-/- mice responded to the intracellular parasite Toxoplasma gondii While the loss of IL-27p28 and its overexpression both result in increased susceptibility to T. gondii, the basis for this phenotype reveals distinct roles for IL-27p28. As a component of IL-27, IL-27p28 is critical to limit infection-induced T cell-mediated pathology, whereas the ectopic expression of IL-27p28 reduced the effector T cell population and had a major inhibitory effect on parasite-specific antibody titers and a failure to control parasite replication in the central nervous system. Indeed, transfer of immune serum to infected IL-27p28 transgenics resulted in reduced parasite burden and pathology. Thus, IL-27p28, independent of its role as a component of IL-27, can act as a negative regulator of humoral and cellular responses during toxoplasmosis.

Mononucleosis Epstein -Barr negativa: variación poco reconocida de enfermedad popular

Se reporta el caso de un paciente joven, inmunocompetente y sin factores de riesgo, con adenopatías cervicales, fiebre, malestar general compatible síndrome mononucleósico. La persistencia de síntomas a pesar de múltiples tratamientos con antibióticos lleva a los médicos tratantes a echar un segundo vistazo. El hallazgo y desenlace, los hallarás aquí.

IL-10 and ICOS Differentially Regulate T Cell Responses in the Brain during Chronic Toxoplasma gondii Infection

Control of chronic CNS infection with the parasite Toxoplasma gondii requires ongoing T cell responses in the brain. Immunosuppressive cytokines are also important for preventing lethal immunopathology during chronic infection. To explore the loss of suppressive cytokines exclusively during the chronic phase of infection, we blocked IL-10R in chronically infected mice. Consistent with previous reports, IL-10R blockade led to severe, fatal tissue destruction associated with widespread changes in the inflammatory response, including increased APC activation, expansion of CD4⁺ T cells, and neutrophil recruitment to the brain. We then sought to identify regulatory mechanisms contributing to IL-10 production, focusing on ICOS, a molecule implicated in IL-10 production. Unexpectedly, ICOS ligand (ICOSL) blockade led to a local expansion of effector T cells in the brain without affecting IL-10 production or APC activation. Instead, we found that ICOSL blockade led to changes in T cells associated with their proliferation and survival. We observed increased expression of IL-2-associated signaling molecules CD25, STAT5 phosphorylation, Ki67, and Bcl-2 in T cells in the brain, along with decreased apoptosis. Interestingly, increases in CD25 and Bcl-2 were not observed following IL-10R blockade. Also, unlike IL-10R blockade, ICOSL blockade led to an expansion of both CD8⁺ and CD4⁺ T cells in the brain, with no expansion of peripheral T cells or neutrophil recruitment to the brain and no severe tissue destruction. Overall, these results suggest that IL-10 and ICOS differentially regulate T cell responses in the brain during chronic T. gondii infection.

Histological Disorganization of Spleen Compartments and Severe Visceral Leishmaniasis

The spleen is a secondary lymphoid organ responsible for immune surveillance against blood-circulating pathogens. Absence of the spleen is associated with increased susceptibility to systemic spread and fatal infection by different pathogens. Severe forms of visceral leishmaniasis are associated with disorganization of spleen compartments where cell interactions essential for splenic immunological function take place. White pulp atrophies, secondary lymphoid follicles and marginal zones vanish, and the boundaries separating white and red pulp blur. Leukocyte populations are reduced or disappear or are replaced by plasma cells. In this paper, we review the published data on spleen disorganization in severe forms of visceral leishmaniasis and propose a histological classification to help the exchange of information among research groups.

Histopathology of murine toxoplasmosis under treatment with dialyzable leukocyte extract

BACKGROUND

Dialyzable leukocyte extracts (DLEs) contain molecules smaller than 10 kDa with biological activity in receptor organisms. Primarily, they participate in the regulation of the Th1 immune response, which is essential for the control of several intracellular infections, such as toxoplasmosis. This disease is associated with congenital infection, encephalitis or systemic infections in immunocompromised individuals. The clinical course of this infection fundamentally depends on a well-regulated immune response and timely treatment with the appropriate drugs.

OBJECTIVE

The aim of this study was to evaluate the effect of treatment with a leukocyte extract, derived from crocodile lymphoid tissue, on the histopathology and brain parasite load in NIH mice that had been infected with cysts of Toxoplasma gondii (ME-49 strain).

METHODS

The treatment was applied during the acute and chronic stages of the infection. Histopathological changes were evaluated in the ileum, liver and spleen at one, four and eight weeks after infection and in the brain at week 8. The parasite load was evaluated by counting the cysts of T. gondii found in the brain.

FINDINGS

Compared to the control mouse group, the mice infected with T. gondii and under treatment with DLE showed less tissue damage, mainly at the intestinal, splenic and hepatic levels. In addition, a greater percentage of survival was observed, and there was a considerable reduction in the parasite load in the brain.

CONCLUSIONS

The results suggest that DLE derived from crocodile is a potential adjunctive therapy in the conventional treatment of toxoplasmosis.

Blood Stage Malaria Disrupts Humoral Immunity to the Pre-erythrocytic Stage Circumsporozoite Protein

Many current malaria vaccines target the pre-erythrocytic stage of infection in the liver. However, in malaria-endemic regions, increased blood stage exposure is associated with decreased vaccine efficacy, thereby challenging current vaccine efforts. We hypothesized that pre-erythrocytic humoral immunity is directly disrupted by blood stage infection. To investigate this possibility, we used Plasmodium-antigen tetramers to analyze B cells after infection with either late liver stage arresting parasites or wild-type parasites that progress to the blood stage. Our data demonstrate that immunoglobulin G (IgG) antibodies against the pre-erythrocytic antigen, circumsporozoite protein (CSP), are generated only in response to the attenuated, but not the wild-type, infection. Further analyses revealed that blood stage malaria inhibits CSP-specific germinal center B cell differentiation and modulates chemokine expression. This results in aberrant memory formation and the loss of a rapid secondary B cell response. These data highlight how immunization with attenuated parasites may drive optimal immunity to malaria.

Downregulated IL-21 Response and T Follicular Helper Cell Exhaustion Correlate with Compromised CD8 T Cell Immunity during Chronic Toxoplasmosis

CD8 T cells are important for maintaining the chronicity of Toxoplasma gondii infection. In a T. gondii encephalitis susceptible model, we recently demonstrated that CD4 T cells play an essential helper role in the maintenance of the effector response and CD8 T cell dysfunctionality was linked to CD4 T cell exhaustion. However, CD4 T cells are constituted of different subsets with various functions and the population(s) providing help to the CD8 T cells has not yet been determined. In the present study, T follicular helper cells (Tfh), which are known to be essential for B cell maturation and are one of the main sources of IL-21, were significantly increased during chronic toxoplasmosis. However, at week 7 p.i., when CD8 T cells are exhausted, the Tfh population exhibited increased expression of several inhibitory receptors and levels of IL-21 in the serum were decreased. The importance of IL-21 in the maintenance of CD8 T cells function after T. gondii infection was further demonstrated in IL-21R KO mouse model. Interestingly, while CD8 T cells from both knockout (KO) and wild-type mice expressed similar levels of PD-1, animals with defective IL-21 signaling exhibited lower polyfunctionality than wild-type controls. This reduced polyfunctional ability observed in CD8 T cells from KO mice was associated with a significant increase in other inhibitory receptors like Tim-3, LAG-3, and 2B4. Furthermore, the animals exhibited greater signs of Toxoplasma reactivation manifested by the reduced number of cysts and increased expression of tachyzoite (replicative form of the parasite) specific genes (SAG1 and ENO2) in the brain. Also, IL-21R KO mice displayed a higher frequency of tachyzoite-infected monocytes in the blood and spleen. Our findings suggest the importance of Tfh and IL-21 during chronic toxoplasmosis and establish a critical role for this cytokine in regulating CD8 T cell dysfunction by preventing the co-expression of multiple inhibitory receptors during chronic parasitic infection.

The Lymphotoxin β Receptor Is Essential for Upregulation of IFN-Induced Guanylate-Binding Proteins and Survival after Toxoplasma gondii Infection

Lymphotoxin β receptor (LTβR) signaling plays an important role in efficient initiation of host responses to a variety of pathogens, encompassing viruses, bacteria, and protozoans via induction of the type I interferon response. The present study reveals that after Toxoplasma gondii infection, LTβR^−/− mice show a substantially reduced survival rate when compared to wild-type mice. LTβR^−/− mice exhibit an increased parasite load and a more pronounced organ pathology. Also, a delayed increase of serum IL-12p40 and a failure of the protective IFNγ response in LTβR^−/− mice were observed. Serum NO levels in LTβR^−/− animals rose later and were markedly decreased compared to wild-type animals. At the transcriptional level, LTβR^−/− animals exhibited a deregulated expression profile of several cytokines known to play a role in activation of innate immunity in T. gondii infection. Importantly, expression of the IFNγ-regulated murine guanylate-binding protein (mGBP) genes was virtually absent in the lungs of LTβR^−/− mice. This demonstrates clearly that the LTβR is essential for the induction of a type II IFN-mediated immune response against T. gondii. The pronounced inability to effectively upregulate host defense effector molecules such as GBPs explains the high mortality rates of LTβR^−/− animals after T. gondii infection.

Comprehensive selection of reference genes for quantitative RT-PCR analysis of murine extramedullary hematopoiesis during development

The purpose of this study was to perform a comprehensive evaluation and selection of reference genes for the study of extramedullary hematopoiesis during development and the early post-natal period. A total of six candidate reference genes (ACTB, GAPDH, HPRT1, PPID, TBP, TUBB3) in four organs (heart, liver, spleen, and thymus) over five perinatal time points (Embryonic days 14.5, 16.5, 18.5, Post-natal days 0, 21) were evaluated by quantitative real-time PCR. The expression stability of the candidate reference genes were analyzed using geNorm, NormFinder, Bestkeeper, Delta CT method, and RefFinder software packages. Detailed methodology for isolation of high quality/purity RNA and analysis is presented. Detailed analysis demonstrated that TBP is the best single reference gene for embryonic samples and HPRT1 is the best single reference gene for post-natal and pooled embryonic and post-natal samples. Organ-level analysis demonstrated that HPRT1 was the most suitable reference gene for heart, liver and thymus samples, while TBP was the best candidate for spleen samples. In general, TUBB3 was consistently the least stable gene for normalization. This is the first study to describe a systematic comprehensive selection of reference genes for murine extramedullary hematopoietic tissues over a developmental time course. We provide suggested reference genes for individual tissues and developmental stages and propose that a combination of reference genes affords flexibility in experimental design and analysis.

Profiling of the perturbed metabolomic state of mouse spleen during acute and chronic toxoplasmosis

Background

Toxoplasma gondii, a common opportunistic protozoan, is a leading cause of illness and mortality among immunosuppressed individuals and during congenital infections. Current therapeutic strategies for toxoplasmosis are not fully effective at curtailing disease progression in these cases. Given the parasite ability to influence host immunity and metabolism, understanding of the metabolic alterations in the host’s immune organs during T. gondii infection may enhance the understanding of the molecular mechanisms that define the pathophysiology of T. gondii infection.

Methods

We investigated the global metabolic changes in the spleen of BALB/c mice at early and late stage of infection with T. gondii using LC-MS/MS-based metabolomics. Multivariate data analysis methods, principal components analysis (PCA) and partial least squares discriminant analysis (PLS-DA), were used to identify metabolites that are influenced by T. gondii infection.

Results

Multivariate analyses clearly separated the metabolites of spleen of infected and control mice. A total of 132 differential metabolites were identified, 23 metabolites from acutely infected versus control mice and 109 metabolites from chronically infected versus control mice. Lipids, hormones, lactones, acids, peptides, antibiotics, alkaloids and natural toxins were the most influenced chemical groups. There were 12 shared differential metabolites between acutely infected versus control mice and chronically infected versus control mice, of which 4,4-Dimethyl-5alpha-cholesta-8,14,24-trien-3beta-ol was significantly upregulated and ubiquinone-8 was significantly downregulated. Major perturbed metabolic pathways included primary bile acid biosynthesis, steroid hormone biosynthesis, biotin metabolism, and steroid biosynthesis, with arachidonic acid metabolism being the most significantly impacted pathway. These metabolic changes suggest a multifactorial nature of the immunometabolic responses of mouse spleen to T. gondii infection.

Conclusions

This study demonstrated that T. gondii infection can cause significant metabolomic alterations in the spleen of infected mice. These findings provide new insights into the molecular mechanisms that underpin the pathogenesis of T. gondii infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2282-6) contains supplementary material, which is available to authorized users.

Transcriptional Responses in the Murine Spleen after Toxoplasma gondii Infection: Inflammasome and Mucus-Associated Genes

The spleen plays an important role in coordinating both adaptive and innate immune responses. Here, the transcriptional response to T. gondii infection in the murine spleen was characterized concerning inflammasome sensors (two different models: seven days after oral or four weeks after intraperitoneal infection). Additionally, Tff1^KO and Tff3^KO mice were investigated because TFF genes are often upregulated during inflammation. The expression of the pattern-recognition receptors Nlrp3, Nlrp12, and Nlrp1a was significantly increased after infection. This increase was diminished in Tff1^KO and Tff3^KO mice pointing towards a positive regulation of the inflammatory response by Tff1 and Tff3. Furthermore, the transcription of Tff1 (encoding a motogenic lectin) and other secretory genes was analyzed, i.e., gastrokines (Gkn), IgG Fc binding protein (Fcgbp), and the mucin Muc2. The corresponding gene products belong to an interactome protecting mucous epithelia. Tff1 was significantly induced after infection, which might increase the motility of immune cells. In contrast, Gkn3, Fcgbp, and Muc2 were downregulated seven days after oral infection; whereas four weeks after i.p. infection only Gkn3 remained downregulated. This might be an indication that Gkn3, Fcgbp, and Muc2 are involved in the transient disruption of the splenic architecture and its reorganization, which is characteristic after T. gondii infection.

T Regulatory Cells Support Plasma Cell Populations in the Bone Marrow

Long-lived plasma cells (PCs) in the bone marrow (BM) are a critical source of antibodies after infection or vaccination, but questions remain about the factors that control PCs. We found that systemic infection alters the BM, greatly reducing PCs and regulatory T (Treg) cells, a population that contributes to immune privilege in the BM. The use of intravital imaging revealed that BM Treg cells display a distinct behavior characterized by sustained co-localization with PCs and CD11c-YFP+ cells. Gene expression profiling indicated that BM Treg cells express high levels of Treg effector molecules, and CTLA-4 deletion in these cells resulted in elevated PCs. Furthermore, preservation of Treg cells during systemic infection prevents PC loss, while Treg cell depletion in uninfected mice reduced PC populations. These studies suggest a role for Treg cells in PC biology and provide a potential target for the modulation of PCs during vaccine-induced humoral responses or autoimmunity.

Endothelial cells are a replicative niche for entry of Toxoplasma gondii to the central nervous system

An important function of the blood-brain barrier is to exclude pathogens from the central nervous system, but some microorganisms benefit from the ability to enter this site. It has been proposed that Toxoplasma gondii can cross biological barriers as a motile extracellular form that uses transcellular or paracellular migration, or by infecting a host cell that then crosses the blood-brain barrier. Unexpectedly, analysis of acutely infected mice revealed significant numbers of free parasites in the blood and the presence of infected endothelial cells in the brain vasculature. The use of diverse transgenic parasites combined with reporter mice and intravital imaging demonstrated that replication in and lysis of endothelial cells precedes invasion of the central nervous system, and highlight a novel mechanism for parasite entry to the central nervous system.

Pathological changes in acute experimental toxoplasmosis with Toxoplasma gondii strains obtained from human cases of congenital disease

There is a lack of studies using Toxoplasma gondii strains isolated from human patients. Here, we present a pathological study of three strains obtained from human cases of congenital toxoplasmosis in Brazil using inbred mice after oral infection with 10 tissue cysts. Multiplex-nested PCR-RFLP of eleven loci revealed atypical genotypes commonly found in Brazil: toxodb #8 for TgCTBr5 and TgCTBr16 strains and toxodb #11 for the TgCTBr9 strain. BALB/c and C57BL/6 mice were evaluated for survival and histological changes during the acute phase of the disease. All mice inoculated with the non-virulent TgCTBR5 strain survived after 30 days, although irreversible tissue damage was found. In contrast, no mice were resistant to infection with the highly virulent TgCTBR9 strain. The TgCTBr16 strain resulted in 80% survival in mice. However, this strain presented low infectivity, especially by the oral route of infection. Despite being identified with the same genotype, TgCTBr5 and TgCTBr16 strains showed biological differences. Histopathologic analysis revealed liver and lungs to be the most affected organs, and the pattern of tissue injury was similar to that found in mice inoculated perorally with strains belonging to clonal genotypes. However, there was a variation in the intensity of ileum lesions according to T. gondii strain and mouse lineage. C57BL/6 mice showed higher susceptibility than BALB/c for histological lesions. Taken together, these results revealed that the pathogenesis of T. gondii strains belonging to atypical genotypes can induce similar tissue damage to those from clonal genotypes, although intrinsic aspects of the strains seem critical to the induction of ileitis in the infected host.

The regulation of T follicular helper responses during infection

Following infection, naïve CD4 T cells can differentiate into various functionally distinct effector and memory subsets, including T follicular helper (TFH) cells that orchestrate germinal center (GC) reactions necessary for high-affinity, pathogen-specific antibody responses. The origins and function of this cell type have been extensively examined in response to subunit immunization with model antigens. More recently, we are beginning to also appreciate the extent to which microbial infections shape the generation, function and maintenance of TFH cells. Here, we review recent advances and highlight additional knowledge gaps in our understanding of how microbial infections influence priming, differentiation, localization and activity of TFH cells following acute and chronic infections.

Stromal infrastructure of the lymph node and coordination of immunity

The initiation of adaptive immune responses depends upon the careful maneuvering of lymphocytes and antigen into and within strategically placed lymph nodes (LNs). Non-hematopoietic stromal cells form the cellular infrastructure that directs this process. Once regarded as merely structural features of lymphoid tissues, these cells are now appreciated as essential regulators of immune cell trafficking, fluid flow, and LN homeostasis. Recent advances in the identification and in vivo targeting of specific stromal populations have resulted in striking new insights to the function of stromal cells and reveal a level of complexity previously unrealized. We discuss here recent discoveries that highlight the pivotal role that stromal cells play in orchestrating immune cell homeostasis and adaptive immunity.

B cell antigen presentation in the initiation of follicular helper T cell and germinal center differentiation

High-affinity class-switched Abs and memory B cells are products of the germinal center (GC). The CD4+ T cell help required for the development and maintenance of the GC is delivered by follicular Th cells (T(FH)), a CD4+ Th cell subset characterized by expression of Bcl-6 and secretion of IL-21. The cellular interactions that mediate differentiation of TFH and GC B cells remain an important area of investigation. We previously showed that MHC class II (MHCII)-dependent dendritic cell Ag presentation is sufficient for the differentiation of a T(FH) intermediate (termed pre-T(FH)), characterized by Bcl-6 expression but lacking IL-21 secretion. In this article, we examine the contributions of MHCII Ag presentation by B cells to T(FH) differentiation and GC responses in several contexts. B cells alone do not efficiently prime naive CD4+ T cells or induce T(FH) after protein immunization; however, during lymphocytic choriomeningitis virus infection, B cells induce T(FH) differentiation despite the lack of effector CD4+ T cell generation. Still, MHCII+ dendritic cells and B cells cooperate for optimal T(FH) and GC B cell differentiation in response to both model Ags and viral infection. This study highlights the roles for B cells in both CD4+ T cell priming and T(FH) differentiation, and demonstrates that different APC subsets work in tandem to mediate the GC response.

Infection-induced changes in hematopoiesis

The bone marrow (BM) is an important site for the interrelated processes of hematopoiesis, granulopoiesis, erythropoiesis, and lymphopoiesis. A wide variety of microbial challenges are associated with profound changes in this compartment that impact on hematopoietic differentiation and mobilization of a variety of cell types. This article reviews some of the key pathways that control BM homeostasis, the infectious and inflammatory processes that affect the BM, and how addressing the knowledge gaps in this area has the potential to widen our comprehension of immune homeostasis.

Immune response and immunopathology during toxoplasmosis

Toxoplasma gondii is a protozoan parasite of medical and veterinary significance that is able to infect any warm-blooded vertebrate host. In addition to its importance to public health, several inherent features of the biology of T. gondii have made it an important model organism to study host-pathogen interactions. One factor is the genetic tractability of the parasite, which allows studies on the microbial factors that affect virulence and allows the development of tools that facilitate immune studies. Additionally, mice are natural hosts for T. gondii, and the availability of numerous reagents to study the murine immune system makes this an ideal experimental system to understand the functions of cytokines and effector mechanisms involved in immunity to intracellular microorganisms. In this article, we will review current knowledge of the innate and adaptive immune responses required for resistance to toxoplasmosis, the events that lead to the development of immunopathology, and the natural regulatory mechanisms that limit excessive inflammation during this infection.