Toxoplasma gondii inhibits toll-like receptor 4 ligand-induced mobilization of intracellular tumor necrosis factor alpha to the surface of mouse peritoneal neutrophils

Human Brain Endothelial Cell-Derived Extracellular Vesicles Reduce Toxoplasma gondii Infection In Vitro in Human Brain and Umbilical Cord Vein Endothelial Cells

The endothelial layer, formed by endothelial cells, performs crucial functions in maintaining homeostasis. The endothelial integrity and function might be compromised due to various causes, including infection by Toxoplasma gondii, leading to an endothelial dysfunction. Toxoplasma gondii is an Apicomplexa parasite that infects a broad range of animals, including humans. This parasite can invade all nucleated cells, as well as endothelial cells. The interaction between this protozoan and endothelial cells can be mediated by different molecules, such as extracellular vesicles (EVs), which may either favor or hinder the infectious process. To investigate this interaction, we evaluated the infection of T. gondii on human brain microvascular endothelial cells (HBMEC) and human umbilical vein endothelial cells (HUVEC), in addition to assessing transcriptional changes. We also featured the EVs secreted by T. gondii and by infected and non-infected HBMEC and HUVEC. Finally, we evaluated the infection of cells stimulated with EVs of parasitic or cellular origin. Our results demonstrated that HUVEC not only exhibit a higher infection rate than HBMEC but also display a more pro-inflammatory transcriptional profile, with increased expression of interleukin-6 (IL6), interleukin-8 (IL8), and monocyte chemotactic protein-1 (MCP1) following infection. Additionally, we observed few differences in the concentration, distribution, and morphology of EVs secreted by both cell types, although their properties in modulating infection varied significantly. When cells were EVs stimulated, EVs from T. gondii promoted an increase in the HBMEC infection, EVs from infected or uninfected HBMEC reduced the infection, whereas EVs from HUVEC had no effect on the infectious process. In conclusion, our data indicate that T. gondii infection induces distinct changes in different endothelial cell types, and EVs from these cells can contribute to the resolution of the 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.

Contributions of HLA haplotypes, IL8 level and Toxoplasma gondii infection in defining celiac disease's phenotypes

BACKGROUND

It is not clear why some patients with coeliac disease (CD) present with severe symptoms and small intestinal mucosal damages while others present with milder symptoms and no frank enteropathy. There is no study to assess the associated factors with mild/severe symptoms and enteropathy. The terminologies like latent, silent and potential are difficult to use and are unrepresentative. In the present study we describe coeliac disease's phenotypes based on HLA haplotypes, IL8 production and past infection with Toxoplasma gondii (T. gondii) infection.

METHODS

In this case-control study, sera originating from 150 healthy subjects and 150 patients diagnosed with CD during the years 2013-14 were analyzed for the presence of antibodies specific T. gondii of the IgG and IgM subclasses. The level of IL8 were measured and HLA-DQ2 and HLA-DQ8 alleles were genotyped. The correlation between these parameters and the damages in intestinal mucosal were assessed using an accepted histopathological classification.

RESULTS

High levels of IgG antibodies against T. gondii were found in the sera of control group compared to the CD group (52.6% vs. 39.4%, P = 0.02). Mean serum levels of IL8 was significantly higher in CD patients compared with control (P ≤ 0.05). By comparing the level of anti- T. gondii IgG and mucosal damage in celiac disease, we found a significant relationship between the severity of mucosal damages and anti- T. gondii IgG level (P = 0.02). No correlation was detected between Toxoplasma gondii infection and types of HLA (P > 0.05). However, patients with severely abnormal histology carried HLA-DQ2 risk alleles (92 patients (61%)) more often than the controls and those with mild histological abnormalities.

CONCLUSIONS

CD patients with severe histological changes had more often Toxoplasma gondii infection than those affected with mild histological features. This suggests that CD's phenotypes are correlated to additional factors like infections and to particular HLA DQ2 alleles that may need additional investigations and potentially will require additional treatment.

NADPH oxidase, MPO, NE, ERK1/2, p38 MAPK and Ca2+ influx are essential for Cryptosporidium parvum-induced NET formation

Cryptosporidium parvum causes a zoonotic infection with worldwide distribution. Besides humans, cryptosporidiosis affects a wide range of animals leading to significant economic losses due to severe enteritis in neonatal livestock. Neutrophil extracellular trap (NET) formation has been demonstrated as an important host effector mechanism of PMN acting against several invading pathogens. In the present study, C. parvum-mediated NET formation was investigated in human and bovine PMN in vitro. We here demonstrate that C. parvum sporozoites indeed trigger NET formation in a time-dependent manner. Thereby, the classical characteristics of NETs were demonstrated by co-localization of extracellular DNA with histones, neutrophil elastase (NE) and myeloperoxidase (MPO). A significant reduction of NET formation was measured following treatments of PMN with NADPH oxidase-, NE- and MPO-inhibitors, confirming the key role of these enzymes in C. parvum-induced NETs. Additionally, sporozoite-triggered NETosis revealed as dependent on intracellular Ca(++) concentration and the ERK 1/2 and p38 MAPK-mediated signaling pathway. Moreover, sporozoite-triggered NET formation led to significant parasite entrapment since 15% of the parasites were immobilized in NET structures. Consequently, PMN-pre-exposed sporozoites showed significantly reduced infectivity for epithelial host cells confirming the capability of NETs to prevent active parasite invasion. Besides NETs, we here show that C. parvum significantly up-regulated CXCL8, IL6, TNF-α and of GM-CSF gene transcription upon sporozoite confrontation, indicating a pivotal role of PMN not only in the bovine and human system but most probably in other final hosts for C. parvum.

Possible role of TLR4 and TLR9 SNPs in protection against congenital toxoplasmosis

The purpose of this investigation was the determination of the distribution of genotypes at single nucleotide polymorphisms (SNPs) of the toll-like receptor 4 (TLR4) and the toll-like receptor 9 (TLR9) in fetuses and newborns congenitally infected with Toxoplasma gondii and the identification of genetic changes predisposing to infection development. The study involved 20 fetuses and newborns with congenital toxoplasmosis and 50 uninfected controls. The levels of IgG and IgM antibodies against T. gondii, as well as IgG avidity, were estimated by enzyme-linked fluorescent assay (ELFA) tests. T. gondii DNA loads in amniotic fluids were assayed by the real-time (RT) quantitative polymerase chain reaction (Q PCR) technique for parasitic B1 gene. TLR4 and TLR9 SNPs were identified using a self-designed multiplex nested PCR-restriction fragment length polymorphism (RFLP) assay. Randomly selected genotypes at SNPs were confirmed by sequencing. All the genotypes were tested for Hardy–Weinberg equilibrium and TLR4 genotypes were analyzed for linkage disequilibrium. A correlation was studied between the genotypes or haplotypes and the development of congenital toxoplasmosis using a logistic regression model. Single SNP analysis showed no statistically significant differences in the distribution of distinct genotypes at the analyzed TLR4 and TLR9 SNPs between T. gondii-infected fetuses and newborns and the controls. Taking into account the prevalence of alleles residing within polymorphic sites, similar prevalence rates were observed in both of the studied groups. The multiple SNP analysis indicated GTG variants at the TLR4 and TLR9 SNPs to be significantly less frequent in offspring with congenital toxoplasmosis than in uninfected offspring (p ≤ 0.0001). TLR4 and TLR9 SNPs seem to be involved in protection against congenital toxoplasmosis.

The circulating proteinase inhibitor α-1 antitrypsin regulates neutrophil degranulation and autoimmunity

Pathological inflammation and autoimmune disease frequently involve elevated neutrophil activity in the absence of infectious agents. Tumor necrosis factor-α (TNF-α) contributes to many of the problems associated with autoimmune diseases. We investigated the ability of serum α-1 antitrypsin (AAT) to control TNF-α biosynthesis and signaling in neutrophils and assessed whether AAT deficiency (AATD) is a TNF-α-related disease. In vitro studies demonstrate that serum AAT coordinates TNF-α intracellular signaling and neutrophil degranulation of tertiary and secondary granules via modulation of ligand-receptor interactions. AATD patients homozygous for the Z allele were characterized by increased activation of the TNF-α system, as demonstrated by increased membrane TNF-α levels and increased plasma concentrations of TNF receptor 1 and neutrophil-released secondary and tertiary granule proteins. The incidence of autoantibodies directed against degranulated lactoferrin and surface protein accessible to these antibodies was increased in ZZ-AATD, leading to an enhanced rate of neutrophil reactive oxygen species production. Treatment of ZZ-AATD individuals with AAT augmentation therapy resulted in decreased membrane TNF-α expression and plasma levels of granule antigenic proteins and immunoglobulin G class autoantibodies. These results provide a mechanism by which AAT augmentation therapy affects TNF-α signaling in the circulating neutrophil, indicating promising potential of this therapy for other TNF-α-related diseases.

Sex bias in susceptibility to MCMV infection: implication of TLR9

Toll-like receptor (TLR)-dependent pathways control the activation of various immune cells and the production of cytokines and chemokines that are important in innate immune control of viruses, including mouse cytomegalovirus (MCMV). Here we report that upon MCMV infection wild-type and TLR7^−/− male mice were more resistant than their female counterparts, while TLR9^−/− male and female mice showed similar susceptibility. Interestingly, 36 h upon MCMV infection TLR9 mRNA expression was higher in male than in female mouse spleens. MCMV infection led to stronger reduction of marginal zone (MZ) B cells, and higher infiltration of plasmacytoid dendritic cells and neutrophils in wild-type male than female mice, while no such sex differences were observed in TLR9^−/− mice. In accordance, the serum levels of KC and MIP-2, major neutrophil chemoattractants, were higher in wild-type, but not in TLR9^−/−, male versus female mice. Wild-type MCMV-infected female mice showed more severe liver inflammation, necrosis and steatosis compared to infected male mice. Our data demonstrate sex differences in susceptibility to MCMV infection, accompanied by a lower activation of the innate immune system in female mice, and can be attributed, at least in a certain degree, to the lower expression of TLR9 in female than male mice.

Host cell signalling and leishmania mechanisms of evasion

Leishmania parasites are able to secure their survival and propagation within their host by altering signalling pathways involved in the ability of macrophages to kill pathogens or to engage adaptive immune system. An important step in this immune evasion process is the activation of host protein tyrosine phosphatase SHP-1 by Leishmania. SHP-1 has been shown to directly inactivate JAK2 and Erk1/2 and to play a role in the negative regulation of several transcription factors involved in macrophage activation. These signalling alterations contribute to the inactivation of critical macrophage functions (e.g., Nitric oxide, IL-12, and TNF-α). Additionally, to interfere with IFN-γ receptor signalling, Leishmania also alters several LPS-mediated responses. Recent findings from our laboratory revealed a pivotal role for SHP-1 in the inhibition of TLR-induced macrophage activation through binding to and inactivating IL-1-receptor-associated kinase 1 (IRAK-1). Furthermore, we identified the binding site as an evolutionarily conserved ITIM-like motif, which we named kinase tyrosine-based inhibitory motif (KTIM). Collectively, a better understanding of the evasion mechanisms utilized by Leishmania parasite could help to develop more efficient antileishmanial therapies in the near future.

CCL3 and viral chemokine-binding protein gg modulate pulmonary inflammation and virus replication during equine herpesvirus 1 infection

CCL3 is a proinflammatory chemokine that mediates many of the cellular changes occurring in pulmonary disease. Here, CCL3(-/-) mice were used to investigate the role of this chemokine during respiratory herpesvirus infection. Compared to wild-type mice, CCL3(-/-) mice infected with the alphaherpesvirus equine herpesvirus 1 (EHV-1) displayed reduced body weight loss but had higher pulmonary viral loads. Lungs from infected CCL3(-/-) mice suffered a milder interstitial pneumonia, and fewer immune cells were recovered from the pulmonary airways after infection. We could also demonstrate that herpesvirus-encoded chemokine-binding glycoprotein G (gG) was capable of inhibiting the chemotactic functions of CCL3. This CCL3-mediated chemotaxis, however, was restored in the presence of gG-specific antibodies, which puts into question the advertised use of gG deletion mutants as marker vaccines. In summary, we concluded that CCL3 is a major player in controlling herpesvirus replication in the target organ, the lung, and does so by evoking a strong inflammatory response. The immunomodulatory activity of CCL3 is balanced by the expression of viral gG, whose chemokine-binding activity is mitigated in secondary infections by the production of anti-gG antibodies.

Herpesvirus Chemokine-Binding Glycoprotein G (gG) Efficiently Inhibits Neutrophil Chemotaxis In Vitro and In Vivo

Glycoprotein G (gG) of alphaherpesviruses has been described to function as a viral chemokine-binding protein (vCKBP). More recently, mutant viruses devoid of gG have been shown to result in increased virulence, but it remained unclear whether the potential of gG to serve as a vCKBP is responsible for this observation. In this study, we used equine herpesvirus type 1 (EHV-1) as a model to study the pathophysiological importance of vCKBP activity. First, in vitro chemotaxis assays studying migration of immune cells, an important function of chemokines, were established. In such assays, supernatants of EHV-1-infected cells significantly inhibited IL-8-induced chemotaxis of equine neutrophils. Identification of gG as the responsible vCKBP was achieved by repeating similar experiments with supernatants from cells infected with a gG-negative mutant, which were unable to alter IL-8-induced equine neutrophil migration. Furthermore, rEHV-1 gG was able to significantly reduce neutrophil migration, establishing gG as a bona fide vCKBP. Second, and importantly, in vivo analyses in a murine model of EHV-1 infection showed that neutrophil migration in the target organ lung was significantly reduced in the presence of gG. In summary, we demonstrate for the first time that EHV-1 gG not only binds to chemokines but is also capable of inhibiting their chemotactic function both in vitro and in vivo, thereby contributing to viral pathogenesis and virulence.

Protozoan encounters with Toll-like receptor signalling pathways: implications for host parasitism

Toll-like receptors (TLRs) have emerged as a major receptor family involved in non-self recognition. They have a vital role in triggering innate immunity and orchestrate the acquired immune response during bacterial and viral infection. However, the role of TLRs during infection with protozoan pathogens is less clear. Nevertheless, our understanding of how these parasitic microorganisms engage the host TLR signalling system has now entered a phase of rapid expansion. This Review describes recent insights into how parasitic protozoans are sensed by TLR molecules, and how the TLR system itself can be targeted by these microbial pathogens for their own survival.