CXCR3-dependent CD4⁺ T cells are required to activate inflammatory monocytes for defense against intestinal infection

Cancer-associated foam cells hamper protective T cell immunity and favor tumor progression in human colon carcinogenesis

BACKGROUND

Colorectal cancer (CRC) remains a significant healthcare burden worldwide, characterized by a complex interplay between obesity and chronic inflammation. While the relationship between CRC, obesity and altered lipid metabolism is not fully understood, there are evidences suggesting a link between them. In this study, we hypothesized that dysregulated lipid metabolism contributes to local accumulation of foam cells (FC) in CRC, which in turn disrupts antitumor immunosurveillance.

METHODS

Tumor infiltrating FC and CD8+ were quantified by digital pathology in patients affected by T2-T4 CRC with any N stage undergoing radical upfront surgery (n=65) and correlated with patients' clinical outcomes. Multiparametric high-resolution flow cytometry analysis and bulk RNAseq of CRC tissue were conducted to evaluate the phenotype and transcriptomic program of immune cell infiltrate in relation to FC accumulation. The immunosuppressive effects of FC and mechanistic studies on FC-associated transforming growth factor-beta (TGF-β) and anti-PD-L1 inhibition were explored using an in-vitro human model of lipid-engulfed macrophages.

RESULTS

FC (large CD68+ Bodipy+ macrophages) accumulated at the tumor margin in CRC samples. FChigh tumors exhibited reduced CD8+ T cells and increased regulatory T cells (Tregs). Functional transcriptional profiling depicted an immunosuppressed milieu characterized by reduced interferon gamma, memory CD8+ T cells, and activated macrophages mirrored by increased T-cell exhaustion and Treg enrichment. Furthermore, FChigh tumor phenotype was independent of standard clinical factors but correlated with high body mass index (BMI) and plasma saturated fatty acid levels. In CD8low tumors, the FChigh phenotype was associated with a 3-year disease-free survival rate of 8.6% compared with 28.7% of FClow (p=0.001). In-vitro studies demonstrated that FC significantly impact on CD8 proliferation in TFG-β dependent manner, while inhibition of TGF-β FC-related factors restored antitumor immunity.

CONCLUSIONS

FC exert immunosuppressive activity through a TGF-β-related pathway, resulting in a CD8-excluded microenvironment and identifying immunosuppressed tumors with worse prognosis in patients with primary CRC. FC association with patient BMI and dyslipidemia might explain the link of CRC with obesity, and offers novel therapeutic and preventive perspectives in this specific clinical setting.

Peripheral blood cellular immunophenotype in depression: a systematic review and meta-analysis

INTRODUCTION

Meta-analyses implicate immune dysfunction in depression confirming increased levels of circulating immune proteins (e.g., cytokines) in depression cases compared to controls. White blood cells (WBC) both produce and are influenced by cytokines, and play key roles in orchestrating innate and adaptive immune responses, but their role in depression remains unclear. Therefore, a systematic review of studies of various WBC subsets in depression is required for a greater understanding of the nature of immune dysfunction in this illness.

METHODS

We searched PubMed and PsycINFO databases (inception to 5th April 2022) and conducted a systematic review and meta-analysis of identified studies comparing absolute count and/or relative percentage of flow cytometry-derived WBC subsets between depression cases and controls. Selected studies were quality assessed. Random-effect meta-analysis was performed.

RESULTS

Thirty-three studies were included and 27 studies (n = 2277) were meta-analysed. We report an increase in mean absolute counts of WBC (seven studies; standardised mean difference [SMD] = 1.07; 95% CI, 0.61-1.53; P < 0.01; I2 = 64%), granulocytes (two studies; SMD = 2.07; 95% CI, 1.45-2.68; P < 0.01; I2 = 0%), neutrophils (four studies; SMD = 0.91; 95% CI, 0.23-1.58; P < 0.01; I2 = 82%), monocytes (seven studies; SMD = 0.60; 95% CI, 0.19-1.01; P < 0.01; I2 = 66%), CD4+ helper T cells (11 studies; SMD = 0.30; 95% CI, 0.15-0.45; P < 0.01; I2 = 0%), natural killer cells (11 studies; SMD = 1.23; 95% CI, 0.38-2.08; P < 0.01; I2 = 95%), B cells (10 studies; SMD = 0.30; 95% CI, 0.03-0.57; P = 0.03; I2 = 56%), and activated T cells (eight studies; SMD = 0.45; 95% CI, 0.24-0.66; P < 0.01; I2 = 0%) in depression, compared to controls. Fewer studies reported relative percentage, indicating increased neutrophils and decreased total lymphocytes, Th1, and Th2 cells in depression.

CONCLUSIONS

Depression is characterised by widespread alterations in circulating myeloid and lymphoid cells, consistent with dysfunction in both innate and adaptive immunity. Immune cells could be useful biomarkers for illness subtyping and patient stratification in future immunotherapy trials of depression, along with cytokines, other biomarkers, and clinical measures.

Single cell analysis via mass cytometry of spontaneous intestinal perforation reveals alterations in small intestinal innate and adaptive mucosal immunity

Introduction

Spontaneous intestinal perforation (SIP) is a poorly understood severe gastrointestinal complications of prematurity which is poorly understood. Extremely premature infants born prior to 28 weeks' gestation develop a localized perforation of the terminal ileum during the first week of life and therapy involves surgery and cessation of enteral feeds. Little is known regardj g the impact of mucosal immune dysfunction on disease pathogenesis.

Methods

We performed mass cytometry time of flight (CyTOF) of small intestinal mucosa of patients with SIP (Gestational age (GA) 24 - 27 weeks, n=8) compared to patients who had surgery for non-SIP conditions (neonatal (GA >36 weeks, n=5 ) and fetal intestine from elective terminations (GA 18-21 weeks, n=4). CyTOF analysis after stimulation of T cells with PMA/Ionomycin was also performed.

Results

We noted changes in innate and adaptive mucosal immunity in SIP. SIP mucosa had an expansion of ckit+ neutrophils, an influx of naïve CD4 and CD8 T cells and a reduction of effector memory T cells. SIP T cells were characterized by reduced CCR6 and CXCR3 expression and increased interferon gamma expression after stimulation.

Discussion

These findings suggest that previously unrecognized immune dysregulation is associated with SIP and should be explored in future studies.

Involvement of chemokine receptor CXCR3 in the defense mechanism against Neospora caninum infection in C57BL/6 mice

C-X-C motif chemokine receptor 3 (CXCR3) is an important receptor controlling the migration of leukocytes, although there is no report regarding its role in Neospora caninum infection. Herein, we investigated the relevance of CXCR3 in the resistance mechanism to N. caninum infection in mice. Wild-type (WT) C57BL/6 mice and CXCR3-knockout (CXCR3KO) mice were used in all experiments. WT mice displayed a high survival rate (100%), while 80% of CXCR3KO mice succumbed to N. caninum infection within 50 days. Compared with WT mice, CXCR3KO mice exhibited significantly lower body weights and higher clinical scores at the subacute stage of infection. Flow cytometric analysis revealed CXCR3KO mice as having significantly increased proportions and numbers of CD11c-positive cells compared with WT mice at 5 days post infection (dpi). However, levels of interleukin-6 and interferon-γ in serum and ascites were similar in all groups at 5 dpi. Furthermore, no differences in parasite load were detected in brain, spleen, lungs or liver tissue of CXCR3KO and WT mice at 5 and 21 dpi. mRNA analysis of brain tissue collected from infected mice at 30 dpi revealed no changes in expression levels of inflammatory response genes. Nevertheless, the brain tissue of infected CXCR3KO mice displayed significant necrosis and microglial activation compared with that of WT mice at 21 dpi. Interestingly, the brain tissue of CXCR3KO mice displayed significantly lower numbers of FoxP3⁺ cells compared with the brain tissue of WT mice at 30 dpi. Accordingly, our study suggests that the lack of active regulatory T cells in brain tissue of infected CXCR3KO mice is the main cause of these mice having severe necrosis and lower survival compared with WT mice. Thus, CXCR3⁺ regulatory T cells may play a crucial role in control of neosporosis.

Intestinal immune responses to commensal and pathogenic protozoa

The physical barrier of the intestine and associated mucosal immunity maintains a delicate homeostatic balance between the host and the external environment by regulating immune responses to commensals, as well as functioning as the first line of defense against pathogenic microorganisms. Understanding the orchestration and characteristics of the intestinal mucosal immune response during commensal or pathological conditions may provide novel insights into the mechanisms underlying microbe-induced immunological tolerance, protection, and/or pathogenesis. Over the last decade, our knowledge about the interface between the host intestinal mucosa and the gut microbiome has been dominated by studies focused on bacterial communities, helminth parasites, and intestinal viruses. In contrast, specifically how commensal and pathogenic protozoa regulate intestinal immunity is less well studied. In this review, we provide an overview of mucosal immune responses induced by intestinal protozoa, with a major focus on the role of different cell types and immune mediators triggered by commensal (Blastocystis spp. and Tritrichomonas spp.) and pathogenic (Toxoplasma gondii, Giardia intestinalis, Cryptosporidium parvum) protozoa. We will discuss how these various protozoa modulate innate and adaptive immune responses induced in experimental models of infection that benefit or harm the host.

Influenza Vaccine Associated with the Gene Expression of T Cell Surface Markers in Human Milk

Background: The function of neonatal T cells is reduced compared to adult T cells. T cells could be transferred to the infants through human milk and compensate for their immature T cells. As the subsets of T cells present in human milk have been incompletely described, this study investigated the association between the maternal factors (influenza vaccine, maternal age, and lactation time), the gene expression of T cell surface markers (cluster of differentiation [CD] and chemokine receptors [CCR]), and the concentrations of T cell-related cytokines in human milk. Materials and Methods: The gene expressions of T cell markers and the concentrations of T cell-related cytokines were determined in milk samples from 16 women. Eight donors received influenza vaccine, and eight were not vaccinated during 2019-2020 for the flu season 2020. Results: For T cell surface markers, the gene expression of CD8A was higher than CD4, CCR6, CD25, CXCR5, CD62L, and CD44 in human milk. CD44 copy gene was lower than CCR7 and CXCR3, while CD4 copy gene was lower than CXCR3 in human milk. Women with influenza vaccine had higher copy genes of CD44, CD8A, CD62L, and CD25 and lower CCR7 copy gene in milk than in women without influenza vaccine. Interleukin-17 concentration in human milk decreased with increasing lactation time. Gene expression of T cell markers and cytokine concentrations varied between lactating women. Conclusions: Although a larger study is needed, it appears that the influenza vaccine is associated with the gene expression of T cell markers in human milk.

Influence of Vitamin D3 Levels and T Cell-Related Cytokines in Human Milk on Coronavirus Disease 2019 Infection in Lactating Women

Background: Vitamin D deficiency was associated with an increased risk of coronavirus disease 2019 (COVID-19) infection. Vitamin D deficient mothers are more likely to have infants with vitamin D deficiency, affecting their immunity and protection against infection. This study aimed at comparing the concentrations of vitamin D3 and T cell-related cytokines in milk between mothers with confirmed COVID-19 polymerase chain reaction (PCR) test, mothers with viral infections suggestive of COVID-19, and mothers without infection. Materials and Methods: Concentrations of vitamin D3 and T cell-related cytokines in milk samples were determined by ELISA from 10 mothers who had a positive COVID-19 PCR test, 10 mothers with viral symptoms suggestive of COVID-19, and 20 mothers without infection. Results: Vitamin D3 concentration in human milk was higher in women without infection than in women with viral symptoms or COVID-19 PCR. Interleukin-2 level in milk was higher in the no-infection group than the COVID-19 PCR group but it did not differ with the viral symptoms group. Vitamin D3 did not correlate with any cytokines in human milk. Prenatal vitamin intake did not affect the vitamin D3 in human milk. The percentage of milk from mothers with <20 ng/mL of vitamin D3 was 50% in the COVID-19 PCR group, 60% in the viral symptoms group, and 5% in the no-infection group. Conclusions: Vitamin D3 level in breast milk may influence maternal immunity against COVID-19 infection. A larger study is needed to evaluate the relationship between vitamin D3 concentration in breast milk, maternal immune response, and the incidence of COVID-19 infection in lactating mothers.

Transcriptomic Analysis of the Effects of Chemokine Receptor CXCR3 Deficiency on Immune Responses in the Mouse Brain during Toxoplasma gondii Infection

The obligate intracellular parasite Toxoplasma gondii infects warm-blooded animals, including humans. We previously revealed through a whole-brain transcriptome analysis that infection with T. gondii in mice causes immune response-associated genes to be upregulated, for instance, chemokines and chemokine receptors such as CXC chemokine receptor 3 (CXCR3) and its ligand CXC chemokine ligand 10 (CXCL10). Here, we describe the effect of CXCR3 on responses against T. gondii infection in the mouse brain. In vivo assays using CXCR3-deficient mice showed that the absence of CXCR3 delayed the normal recovery of body weight and increased the brain parasite burden, suggesting that CXCR3 plays a role in the control of pathology in the brain, the site where chronic infection occurs. Therefore, to further analyze the function of CXCR3 in the brain, we profiled the gene expression patterns of primary astrocytes and microglia by RNA sequencing and subsequent analyses. CXCR3 deficiency impaired the normal upregulation of immune-related genes during T. gondii infection, in astrocytes and microglia alike. Collectively, our results suggest that the immune-related genes upregulated by CXCR3 perform a particular role in controlling pathology when the host is chronically infected with T. gondii in the brain.

Induction of IL-12p40 and type 1 immunity by Toxoplasma gondii in the absence of the TLR-MyD88 signaling cascade

Toxoplasma gondii is an orally acquired pathogen that induces strong IFN-γ based immunity conferring protection but that can also be the cause of immunopathology. The response in mice is driven in part by well-characterized MyD88-dependent signaling pathways. Here we focus on induction of less well understood immune responses that do not involve this Toll-like receptor (TLR)/IL-1 family receptor adaptor molecule, in particular as they occur in the intestinal mucosa. Using eYFP-IL-12p40 reporter mice on an MyD88^-/- background, we identified dendritic cells, macrophages, and neutrophils as cellular sources of MyD88-independent IL-12 after peroral T. gondii infection. Infection-induced IL-12 was lower in the absence of MyD88, but was still clearly above noninfected levels. Overall, this carried through to the IFN-γ response, which while generally decreased was still remarkably robust in the absence of MyD88. In the latter mice, IL-12 was strictly required to induce type I immunity. Type 1 and type 3 innate lymphoid cells (ILC), CD4⁺ T cells, and CD8⁺ T cells each contributed to the IFN-γ pool. We report that ILC3 were expanded in infected MyD88^-/- mice relative to their MyD88^+/+ counterparts, suggesting a compensatory response triggered by loss of MyD88. Furthermore, bacterial flagellin and Toxoplasma specific CD4⁺ T cell populations in the lamina propria expanded in response to infection in both WT and KO mice. Finally, we show that My88-independent IL-12 and T cell mediated IFN-γ production require the presence of the intestinal microbiota. Our results identify MyD88-independent intestinal immune pathways induced by T. gondii including myeloid cell derived IL-12 production, downstream type I immunity and IFN-γ production by ILC1, ILC3, and T lymphocytes. Collectively, our data reveal an underlying network of immune responses that do not involve signaling through MyD88.

Toxoplasma gondii is an apicomplexan parasite estimated to infect 30–50% of humans worldwide. The parasite normally establishes latency in brain and muscle tissue marked by persistent asymptomatic infection. T. gondii masterfully strikes a balance between eliciting strong, anti-parasite immunity while also persisting in the host. Although the murine host recognizes Toxoplasma profilin via MyD88 and Toll-like receptors 11/12, humans lack these receptors and MyD88 deficient patients retain resistance to T. gondii infection. Given these observations, it is important to identify MyD88 independent pathways of immunity. Using an oral infection mouse model, we identified cellular sources of IL-12 and IFN-γ, two cytokines that are essential for host resistance to this microbial pathogen. We determined how these responses are impacted by the presence and absence of MyD88 and the intestinal microbiota. Our data demonstrate that T. gondii triggers MyD88-independent innate and adaptive immunity in the intestinal mucosa that requires the presence of intestinal microbes. These pathways may be conserved among species and understanding how they work in rodents will likely help determine how humans recognize and respond to T. gondii infection.

Role of interferon gamma in SARS-CoV-2-positive patients with parasitic infections

Background

By 27 June 2020, almost half a million people had died due to COVID-19 infections. The susceptibility and severity of infection vary significantly across nations. The contribution of chronic viral and parasitic infections to immune homeostasis remains a concern. By investigating the role of interferon (IFN)-γ, we conducted this study to understand the connection between the decrease in numbers and severity of COVID-19 cases within parasitic endemic regions. Our research included 375 patients referred to hospitals for diagnosis of COVID-19 infection. Patients were subjected to full investigations, in particular severe acute respiratory syndrome coronavirus-2 nucleic acid and Toxoplasma IgM and IgG antibody detection, stool examination, and quantitative IFN-γ measurement.

Results

The majority of the studied cases had chest manifestation either alone (54.7%) or in association with gastrointestinal (GIT) manifestations (19.7%), whereas 25.6% had GIT symptoms. We reported parasitic infections in 72.8% of mild COVID-19 cases and 20.7% of severe cases. Toxoplasma gondii, Cryptosporidium, Blastocyst, and Giardia were the most common parasitic infections among the COVID-19 cases studied.

Conclusion

The remarkable adaptation of human immune response to COVID-19 infection by parasitic infections with high levels of IFN-γ was observed in moderate cases compared with low levels in extreme cases. The potential therapeutic efforts aimed at the role of parasitic infection in immune system modulation are needed if this hypothesis is confirmed.

SHP2 drives inflammation-triggered insulin resistance by reshaping tissue macrophage populations

Insulin resistance is a key event in type 2 diabetes onset and a major comorbidity of obesity. It results from a combination of fat excess-triggered defects, including lipotoxicity and metaflammation, but the causal mechanisms remain difficult to identify. Here, we report that hyperactivation of the tyrosine phosphatase SHP2 found in Noonan syndrome (NS) led to an unsuspected insulin resistance profile uncoupled from altered lipid management (for example, obesity or ectopic lipid deposits) in both patients and mice. Functional exploration of an NS mouse model revealed this insulin resistance phenotype correlated with constitutive inflammation of tissues involved in the regulation of glucose metabolism. Bone marrow transplantation and macrophage depletion improved glucose homeostasis and decreased metaflammation in the mice, highlighting a key role of macrophages. In-depth analysis of bone marrow-derived macrophages in vitro and liver macrophages showed that hyperactive SHP2 promoted a proinflammatory phenotype, modified resident macrophage homeostasis, and triggered monocyte infiltration. Consistent with a role of SHP2 in promoting inflammation-driven insulin resistance, pharmaceutical SHP2 inhibition in obese diabetic mice improved insulin sensitivity even better than conventional antidiabetic molecules by specifically reducing metaflammation and alleviating macrophage activation. Together, these results reveal that SHP2 hyperactivation leads to inflammation-triggered metabolic impairments and highlight the therapeutical potential of SHP2 inhibition to ameliorate insulin resistance.

Transcriptomics analysis of Toxoplasma gondii-infected mouse macrophages reveals coding and noncoding signatures in the presence and absence of MyD88

BACKGROUND

Toxoplasma gondii is a globally distributed protozoan parasite that establishes life-long asymptomatic infection in humans, often emerging as a life-threatening opportunistic pathogen during immunodeficiency. As an intracellular microbe, Toxoplasma establishes an intimate relationship with its host cell from the outset of infection. Macrophages are targets of infection and they are important in early innate immunity and possibly parasite dissemination throughout the host. Here, we employ an RNA-sequencing approach to identify host and parasite transcriptional responses during infection of mouse bone marrow-derived macrophages (BMDM). We incorporated into our analysis infection with the high virulence Type I RH strain and the low virulence Type II strain PTG. Because the well-known TLR-MyD88 signaling axis is likely of less importance in humans, we examined transcriptional responses in both MyD88+/+ and MyD88-/- BMDM. Long noncoding (lnc) RNA molecules are emerging as key regulators in infection and immunity, and were, therefore, included in our analysis.

RESULTS

We found significantly more host genes were differentially expressed in response to the highly virulent RH strain rather than with the less virulent PTG strain (335 versus 74 protein coding genes for RH and PTG, respectively). Enriched in these protein coding genes were subsets associated with the immune response as well as cell adhesion and migration. We identified 249 and 83 non-coding RNAs as differentially expressed during infection with RH and PTG strains, respectively. Although the majority of these are of unknown function, one conserved lncRNA termed mir17hg encodes the mir17 microRNA gene cluster that has been implicated in down-regulating host cell apoptosis during T. gondii infection. Only a minimal number of transcripts were differentially expressed between MyD88 knockout and wild type cells. However, several immune genes were among the differences. While transcripts for parasite secretory proteins were amongst the most highly expressed T. gondii genes during infection, no differentially expressed parasite genes were identified when comparing infection in MyD88 knockout and wild type host BMDM.

CONCLUSIONS

The large dataset presented here lays the groundwork for continued studies on both the MyD88-independent immune response and the function of lncRNAs during Toxoplasma gondii infection.

CXCR3-Dependent Immune Pathology in Mice following Infection with Toxoplasma gondii during Early Pregnancy

Toxoplasmosis is a worldwide zoonosis caused by the obligate intracellular parasite Toxoplasma gondii The symptoms of congenital toxoplasmosis range from embryonic death and resorption to subclinical infection, but the mechanism of disease onset remains unclear. C-X-C motif chemokine receptor 3 (CXCR3) is highly expressed in Th1-associated immune cells and plays an important role in the trafficking and activation of immune cells. However, the roles of CXCR3 in T. gondii-induced fetal loss and the molecular mechanism of embryo resorption remain poorly understood. In this study, we investigated the role of CXCR3 in fetal wastage caused by T. gondii infection using CXCR3-deficient (CXCR3^-/-) mice. CXCR3^-/- and wild-type pregnant mice were inoculated intraperitoneally with T. gondii tachyzoites on day 3.5 of gestation (Gd3.5). Pregnancy rates decreased as the pregnancy progressed in both infected groups; however, infected CXCR3^-/- mice showed a significant fetal loss at Gd13.5 compared with that at Gd7.5. All embryos of the infected groups showed necrosis, and embryo resorption was significantly increased in infected CXCR3^-/- compared with wild-type mice at Gd13.5. The parasite load of fetoplacental tissues was significantly increased in CXCR3^-/- mice at Gd10.5. Moreover, mRNA expression levels of inducible nitric oxide synthase were significantly increased in fetoplacental tissues from infected wild-type mice compared to infected CXCR3^-/- mice following the infection. These results suggested that CXCR3-dependent immune responses provide anti-Toxoplasma activity and play an essential role in reducing embryo resorption and fetal loss caused by T. gondii infection during early pregnancy.

From Initiators to Effectors: Roadmap Through the Intestine During Encounter of Toxoplasma gondii With the Mucosal Immune System

The gastrointestinal tract is a major portal of entry for many pathogens, including the protozoan parasite Toxoplasma gondii. Billions of people worldwide have acquired T. gondii at some point in their life, and for the vast majority this has led to latent infection in the central nervous system. The first line of host defense against Toxoplasma is located within the intestinal mucosa. Appropriate coordination of responses by the intestinal epithelium, intraepithelial lymphocytes, and lamina propria cells results in an inflammatory response that controls acute infection. Under some conditions, infection elicits bacterial dysbiosis and immune-mediated tissue damage in the intestine. Here, we discuss the complex interactions between the microbiota, the epithelium, as well as innate and adaptive immune cells in the intestinal mucosa that induce protective immunity, and that sometimes switch to inflammatory pathology as T. gondii encounters tissues of the gut.

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

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

Peripheral Blood Cell-Stratified Subgroups of Inflamed Depression

BACKGROUND

Depression has been associated with increased inflammatory proteins, but changes in circulating immune cells are less well defined.

METHODS

We used multiparametric flow cytometry to count 14 subsets of peripheral blood cells in 206 depression cases and 77 age- and sex-matched controls (N = 283). We used univariate and multivariate analyses to investigate the immunophenotypes associated with depression and depression severity.

RESULTS

Depression cases, compared with controls, had significantly increased immune cell counts, especially neutrophils, CD4+ T cells, and monocytes, and increased inflammatory proteins (C-reactive protein and interleukin-6). Within-group analysis of cases demonstrated significant associations between the severity of depressive symptoms and increased myeloid and CD4+ T-cell counts. Depression cases were partitioned into 2 subgroups by forced binary clustering of cell counts: the inflamed depression subgroup (n = 81 out of 206; 39%) had increased monocyte, CD4+, and neutrophil counts; increased C-reactive protein and interleukin-6; and more severe depression than the uninflamed majority of cases. Relaxing the presumption of a binary classification, data-driven analysis identified 4 subgroups of depression cases, 2 of which (n = 38 and n = 100; 67% collectively) were associated with increased inflammatory proteins and more severe depression but differed in terms of myeloid and lymphoid cell counts. Results were robust to potentially confounding effects of age, sex, body mass index, recent infection, and tobacco use.

CONCLUSIONS

Peripheral immune cell counts were used to distinguish inflamed and uninflamed subgroups of depression and to indicate that there may be mechanistically distinct subgroups of inflamed depression.

CXCR3 chemokine receptor contributes to specific CD8+ T cell activation by pDC during infection with intracellular pathogens

Chemokine receptor type 3 (CXCR3) plays an important role in CD8⁺ T cells migration during intracellular infections, such as Trypanosoma cruzi. In addition to chemotaxis, CXCR3 receptor has been described as important to the interaction between antigen-presenting cells and effector cells. We hypothesized that CXCR3 is fundamental to T. cruzi-specific CD8⁺ T cell activation, migration and effector function. Anti-CXCR3 neutralizing antibody administration to acutely T. cruzi-infected mice decreased the number of specific CD8⁺ T cells in the spleen, and those cells had impaired in activation and cytokine production but unaltered proliferative response. In addition, anti-CXCR3-treated mice showed decreased frequency of CD8⁺ T cells in the heart and numbers of plasmacytoid dendritic cells in spleen and lymph node. As CD8⁺ T cells interacted with plasmacytoid dendritic cells during infection by T. cruzi, we suggest that anti-CXCR3 treatment lowers the quantity of plasmacytoid dendritic cells, which may contribute to impair the prime of CD8⁺ T cells. Understanding which molecules and mechanisms guide CD8⁺ T cell activation and migration might be a key to vaccine development against Chagas disease as those cells play an important role in T. cruzi infection control.

Inflammatory chemokine receptors such as CXCR3 play an important role in T lymphocytes migration into an infected tissue during Th1 response. Recently, the role of CXCR3 as a co-stimulatory molecule was demonstrated, and T lymphocytes from CXCR3 deficient mice had impaired effector function. CXCR3 receptor was highly expressed on specific CD8⁺ T cells after challenge with T. cruzi, and the hypothesis of that molecule is important for CD8⁺ T cells activation, migration and functionality was raised. We used the anti-CXCR3 neutralizing antibody approach and demonstrated that C57BL/6 treated mice died very quickly due to T. cruzi infection, and specific CD8⁺ T cells had decreased effector phenotyping, cytokine production, and cytotoxicity. In addition, anti-CXCR3 treatment decreased the number of dendritic plasmacytoid cells in the lymphoid tissues. The lower quantity of dendritic plasmacytoid cells in those tissues might contribute to the decrease in CD8⁺ T cells activation. Overall, CXCR3 molecule seems to be an important molecule to be explored during vaccine against Chagas disease strategies.

Toxoplasma gondii dense granule protein GRA24 drives MyD88-independent p38 MAPK activation, IL-12 production and induction of protective immunity

The apicomplexan Toxoplasma gondii induces strong protective immunity dependent upon recognition by Toll-like receptors (TLR)11 and 12 operating in conjunction with MyD88 in the murine host. However, TLR11 and 12 proteins are not present in humans, inspiring us to investigate MyD88-independent pathways of resistance. Using bicistronic IL-12-YFP reporter mice on MyD88+/+ and MyD88-/- genetic backgrounds, we show that CD11c+MHCII+F4/80- dendritic cells, F4/80+ macrophages, and Ly6G+ neutrophils were the dominant cellular sources of IL-12 in both wild type and MyD88 deficient mice after parasite challenge. Parasite dense granule protein GRA24 induces p38 MAPK activation and subsequent IL-12 production in host macrophages. We show that Toxoplasma triggers an early and late p38 MAPK phosphorylation response in MyD88+/+ and MyD88-/- bone marrow-derived macrophages. Using the uracil auxotrophic Type I T. gondii strain cps1-1, we demonstrate that the late response does not require active parasite proliferation, but strictly depends upon GRA24. By i. p. inoculation with cps1-1 and cps1-1:Δgra24, we identified unique subsets of chemokines and cytokines that were up and downregulated by GRA24. Finally, we demonstrate that cps1-1 triggers a strong host-protective GRA24-dependent Th1 response in the absence of MyD88. Our data identify GRA24 as a major mediator of p38 MAPK activation, IL-12 induction and protective immunity that operates independently of the TLR/MyD88 cascade.

The evolving role of T-bet in resistance to infection

The identification of T-bet as a key transcription factor associated with the development of IFNγ-producing CD4⁺ T cells predicted a crucial role for T-bet in cell-mediated immunity and in resistance to many intracellular infections. This idea was reinforced by initial reports showing that T-bet-deficient mice were more susceptible to pathogens that survived within the lysosomal system of macrophages. However, subsequent studies revealed IFNγ-dependent, T-bet-independent pathways of resistance to diverse classes of microorganisms that occupy other intracellular niches. Consequently, a more complex picture has emerged of how T-bet and the related transcription factor eomesodermin (EOMES) coordinate many facets of the immune response to bona fide pathogens as well as commensals. This article provides an overview of the discovery and evolutionary relationship between T-bet and EOMES and highlights the studies that have uncovered broader functions of T-bet in innate and adaptive immunity and in the development of the effector and memory T cell populations that mediate long-term resistance to infection.

Stress keratin 17 enhances papillomavirus infection-induced disease by downregulating T cell recruitment

High-risk human papillomaviruses (HPVs) cause 5% of human cancers. Despite the availability of HPV vaccines, there remains a strong urgency to find ways to treat persistent HPV infections, as current HPV vaccines are not therapeutic for individuals already infected. We used a mouse papillomavirus infection model to characterize virus-host interactions. We found that mouse papillomavirus (MmuPV1) suppresses host immune responses via overexpression of stress keratins. In mice deficient for stress keratin K17 (K17KO), we observed rapid regression of papillomas dependent on T cells. Cellular genes involved in immune response were differentially expressed in the papillomas arising on the K17KO mice correlating with increased numbers of infiltrating CD8+ T cells and upregulation of IFNγ-related genes, including CXCL9 and CXCL10, prior to complete regression. Blocking the receptor for CXCL9/CXCL10 prevented early regression. Our data provide a novel mechanism by which papillomavirus-infected cells evade host immunity and defines new therapeutic targets for treating persistent papillomavirus infections.

CXCR3 chemokine receptor guides Trypanosoma cruzi-specific T-cells triggered by DNA/adenovirus ASP2 vaccine to heart tissue after challenge

CD8+ T lymphocytes play an important role in controlling infections by intracellular pathogens. Chemokines and their receptors are crucial for the migration of CD8+ T-lymphocytes, which are the main IFNγ producers and cytotoxic effectors cells. Although the participation of chemokine ligands and receptors has been largely explored in viral infection, much less is known in infection by Trypanosoma cruzi, the causative agent of Chagas disease. After T. cruzi infection, CXCR3 chemokine receptor is highly expressed on the surface of CD8+ T-lymphocytes. Here, we hypothesized that CXCR3 is a key molecule for migration of parasite-specific CD8+ T-cells towards infected tissues, where they may play their effector activities. Using a model of induction of resistance to highly susceptible A/Sn mice using an ASP2-carrying DNA/adenovirus prime-boost strategy, we showed that CXCR3 expression was upregulated on CD8+ T-cells, which selectively migrated towards its ligands CXCL9 and CXCL10. Anti-CXCR3 administration reversed the vaccine-induced resistance to T. cruzi infection in a way associated with hampered cytotoxic activity and increased proapoptotic markers on the H2KK-restricted TEWETGQI-specific CD8+ T-cells. Furthermore, CXCR3 receptor critically guided TEWETGQI-specific effector CD8+ T-cells to the infected heart tissue that express CXCL9 and CXCL10. Overall, our study pointed CXCR3 and its ligands as key molecules to drive T. cruzi-specific effector CD8+ T-cells into the infected heart tissue. The unveiling of the process driving cell migration and colonization of infected tissues by pathogen-specific effector T-cells is a crucial requirement to the development of vaccine strategies.

Infection-Induced Intestinal Dysbiosis Is Mediated by Macrophage Activation and Nitrate Production

Oral infection of C57BL/6J mice with Toxoplasma gondii results in a marked bacterial dysbiosis and the development of severe pathology in the distal small intestine that is dependent on CD4+ T cells and interferon gamma (IFN-γ). This dysbiosis and bacterial translocation contribute to the development of ileal pathology, but the factors that support the bloom of bacterial pathobionts are unclear. The use of microbial community profiling and shotgun metagenomics revealed that Toxoplasma infection induces a dysbiosis dominated by Enterobacteriaceae and an increased potential for nitrate respiration. In vivo experiments using bacterial metabolic mutants revealed that during this infection, host-derived nitrate supports the expansion of Enterobacteriaceae in the ileum via nitrate respiration. Additional experiments with infected mice indicate that the IFN-γ/STAT1/iNOS axis, while essential for parasite control, also supplies a pool of nitrate that serves as a source for anaerobic respiration and supports overgrowth of Enterobacteriaceae Together, these data reveal a trade-off in intestinal immunity after oral infection of C57BL/6J mice with T. gondii, in which inducible nitric oxide synthase (iNOS) is required for parasite control, while this host enzyme is responsible for specific modification of the composition of the microbiome that contributes to pathology.IMPORTANCEToxoplasma gondii is a protozoan parasite and a leading cause of foodborne illness. Infection is initiated when the parasite invades the intestinal epithelium, and in many host species, this leads to intense inflammation and a dramatic disruption of the normal microbial ecosystem that resides in the healthy gut (the so-called microbiome). One characteristic change in the microbiome during infection with Toxoplasma-as well as numerous other pathogens-is the overgrowth of Escherichia coli or similar bacteria and a breakdown of commensal containment leading to seeding of peripheral organs with gut bacteria and subsequent sepsis. Our findings provide one clear explanation for how this process is regulated, thereby improving our understanding of the relationship between parasite infection, inflammation, and disease. Furthermore, our results could serve as the basis for the development of novel therapeutics to reduce the potential for harmful bacteria to bloom in the gut during infection.

T Cell Phenotype and T Cell Receptor Repertoire in Patients with Major Depressive Disorder

While a link between inflammation and the development of neuropsychiatric disorders, including major depressive disorder (MDD) is supported by a growing body of evidence, little is known about the contribution of aberrant adaptive immunity in this context. Here, we conducted in-depth characterization of T cell phenotype and T cell receptor (TCR) repertoire in MDD. For this cross-sectional case–control study, we recruited antidepressant-free patients with MDD without any somatic or psychiatric comorbidities (n = 20), who were individually matched for sex, age, body mass index, and smoking status to a non-depressed control subject (n = 20). T cell phenotype and repertoire were interrogated using a combination of flow cytometry, gene expression analysis, and next generation sequencing. T cells from MDD patients showed significantly lower surface expression of the chemokine receptors CXCR3 and CCR6, which are known to be central to T cell differentiation and trafficking. In addition, we observed a shift within the CD4⁺ T cell compartment characterized by a higher frequency of CD4⁺CD25^highCD127^low/− cells and higher FOXP3 mRNA expression in purified CD4⁺ T cells obtained from patients with MDD. Finally, flow cytometry-based TCR Vβ repertoire analysis indicated a less diverse CD4⁺ T cell repertoire in MDD, which was corroborated by next generation sequencing of the TCR β chain CDR3 region. Overall, these results suggest that T cell phenotype and TCR utilization are skewed on several levels in patients with MDD. Our study identifies putative cellular and molecular signatures of dysregulated adaptive immunity and reinforces the notion that T cells are a pathophysiologically relevant cell population in this disorder.

Immunocompetent host develops mild intestinal inflammation in acute infection with Toxoplasma gondii

Toxoplasma gondii (T. gondii) is the causative agent of toxoplasmosis, common zoonosis among vertebrates and high incidence worldwide. During the infection, the parasite needs to transpose the intestinal barrier to spread throughout the body, which may be a trigger for an inflammatory reaction. This work evaluated the inflammatory alterations of early T. gondii infection in peripheral blood cells, in the mesenteric microcirculation, and small intestinal tissue by measurement of MPO (myeloperoxidase) activity and NO (nitric oxide) level in rats. Animals were randomly assigned into control group (CG) that received saline orally and groups infected with 5,000 oocysts for 6 (G6), 12 (G12), 24 (G24), 48 (G48) and 72 hours (G72). Blood samples were collected for total and differential leukocyte count. Intravital microscopy was performed in the mesentery to evaluate rolling and adhesion of leukocytes. After euthanasia, 0.5cm of the duodenum, jejunum and ileum were collected for the determination of MPO activity, NO level and PCR to identify the parasite DNA and also the mesentery were collected to perform immunohistochemistry on frozen sections to quantify adhesion molecules ICAM-1, PECAM-1 and P-Selectin. The parasite DNA was identified in all infected groups and there was an increase in leukocytes in the peripheral blood and in expression of ICAM-1 and PECAM-1 in G6 and G12, however, the expression of P-selectin was reduced in G12. Leukocytes are in rolling process during the first 12 hours and they are adhered at 24 hours post-infection. The activity of MPO increased in the duodenum at 12 hours, and NO increased in the jejunum in G72 and ileum in G24, G48 and G72. Our study demonstrated that T. gondii initiates the infection precociously (at 6 hours) leading to a systemic activation of innate immune response resulting in mild inflammation in a less susceptible experimental model.

Transplantation of fecal microbiota from patients with irritable bowel syndrome alters gut function and behavior in recipient mice

Irritable bowel syndrome (IBS) is a common disorder characterized by altered gut function and often is accompanied by comorbid anxiety. Although changes in the gut microbiota have been documented, their relevance to the clinical expression of IBS is unknown. To evaluate a functional role for commensal gut bacteria in IBS, we colonized germ-free mice with the fecal microbiota from healthy control individuals or IBS patients with diarrhea (IBS-D), with or without anxiety, and monitored gut function and behavior in the transplanted mice. Microbiota profiles in recipient mice clustered according to the microbiota profiles of the human donors. Mice receiving the IBS-D fecal microbiota showed a taxonomically similar microbial composition to that of mice receiving the healthy control fecal microbiota. However, IBS-D mice showed different serum metabolomic profiles. Mice receiving the IBS-D fecal microbiota, but not the healthy control fecal microbiota, exhibited faster gastrointestinal transit, intestinal barrier dysfunction, innate immune activation, and anxiety-like behavior. These results indicate the potential of the gut microbiota to contribute to both intestinal and behavioral manifestations of IBS-D and suggest the potential value of microbiota-directed therapies in IBS patients.

Diversity and functions of intestinal mononuclear phagocytes

The intestinal lamina propria (LP) contains a diverse array of mononuclear phagocyte (MNP) subsets, including conventional dendritic cells (cDC), monocytes and tissue-resident macrophages (mφ) that collectively play an essential role in mucosal homeostasis, infection and inflammation. In the current review we discuss the function of intestinal cDC and monocyte-derived MNP, highlighting how these subsets play several non-redundant roles in the regulation of intestinal immune responses. While much remains to be learnt, recent findings also underline how the various populations of MNP adapt to deal with the challenges specific to their environment. Understanding these processes should help target individual subsets for 'fine tuning' immunological responses within the intestine, a process that may be of relevance both for the treatment of inflammatory bowel disease (IBD) and for optimized vaccine design.

Transgenic T cell-specific expression of CXCR3 enhances splenic and hepatic T cell accumulation but does not affect the outcome of visceral leishmaniasis

The outcome of visceral leishmaniasis, caused by parasite Leishmania donovani, depends on the recruitment of leishmanicidal Th1 cells. Chemokine receptor CXCR3, preferentially expressed by Th1 cells, is critical for migration of these T cells during infection. During chronic VL, there is a decrease in the presence of CXCR3-expressing CD4+ T cells in the spleen, which is associated with high parasitic burden in this organ. We therefore examined whether T cell-specific expression of CXCR3 in mice (CXCR3Tg) would promote resistance to VL. L. donovani infected CXCR3Tg mice showed increased accumulation of T cells in the spleens compared to WT littermates (CXCR3+/+). However, CXCR3+ T cells from CXCR3Tg mice showed low CD69 expression and these mice developed fewer granulomas. Additionally, both groups of mice showed similar cytokine profiles and parasitic burdens during the course of infection. In summary, although T cell-specific expression of CXCR3 promoted the accumulation of CXCR3-expressing T cells during L. donovani infection, this did not enhance resistance to VL.

The role of chemokines and their receptors during protist parasite infections

Protists are a diverse collection of eukaryotic organisms that account for a significant global infection burden. Often, the immune responses mounted against these parasites cause excessive inflammation and therefore pathology in the host. Elucidating the mechanisms of both protective and harmful immune responses is complex, and often relies of the use of animal models. In any immune response, leucocyte trafficking to the site of infection, or inflammation, is paramount, and this involves the production of chemokines, small chemotactic cytokines of approximately 8–10 kDa in size, which bind to specific chemokine receptors to induce leucocyte movement. Herein, the scientific literature investigating the role of chemokines in the propagation of immune responses against key protist infections will be reviewed, focussing onPlasmodiumspecies,Toxoplasma gondii, Leishmaniaspecies andCryptosporidiumspecies. Interestingly, many studies find that chemokines can in fact, promote parasite survival in the host, by drawing in leucocytes for spread and further replication. Recent developments in drug targeting against chemokine receptors highlights the need for further understanding of the role played by these proteins and their receptors in many different diseases.

MIF Promotes Classical Activation and Conversion of Inflammatory Ly6C(high) Monocytes into TipDCs during Murine Toxoplasmosis

Macrophage migration inhibitory factor (MIF) mediates immunity against Toxoplasma gondii infection by inducing inflammatory cytokines required to control the parasite replication. However, the role of this inflammatory mediator in the cell-mediated immune response against this infection is still poorly understood. Here, we used T. gondii-infected WT and Mif^−/− mice to analyze the role of MIF in the maturation of CD11b⁺ and CD8α⁺ dendritic cells (DCs). We found that MIF promotes maturation of CD11b⁺ but not CD8α⁺ DCs, by inducing IL-12p70 production and CD86 expression. Infected Mif^−/− mice showed significantly lower numbers of TNF and inducible nitric oxide synthase- (iNOS-) producing DCs (TipDCs) compared to infected WT mice. The adoptive transfer of Ly6C^high monocytes into infected WT or Mif^−/− mice demonstrated that MIF participates in the differentiation of Ly6C^high monocytes into TipDCs. In addition, infected Mif^−/− mice display a lower percentage of IFN-γ-producing natural killer (NK) cells compared to WT mice, which is associated with reducing numbers of TipDCs in Mif^−/− mice. Furthermore, administration of recombinant MIF (rMIF) into T. gondii-infected Mif^−/− mice restored the numbers of TipDCs and reversed the susceptible phenotype of Mif^−/− mice. Collectively, these results demonstrate an important role for MIF inducing cell-mediated immunity to T. gondii infection.

Beta-catenin signaling drives differentiation and proinflammatory function of IRF8-dependent dendritic cells

Beta-catenin signaling has recently been tied to the emergence of tolerogenic dendritic cells (DCs). In this article, we demonstrate a novel role for beta-catenin in directing DC subset development through IFN regulatory factor 8 (IRF8) activation. We found that splenic DC precursors express beta-catenin, and DCs from mice with CD11c-specific constitutive beta-catenin activation upregulated IRF8 through targeting of the Irf8 promoter, leading to in vivo expansion of IRF8-dependent CD8a+, plasmacytoid, and CD103+ CD11b2 DCs. beta-catenin–stabilized CD8a+ DCs secreted elevated IL-12 upon in vitro microbial stimulation, and pharmacological beta-catenin inhibition blocked this response in wild-type cells. Upon infections with Toxoplasma gondii and vaccinia virus, mice with stabilized DC beta-catenin displayed abnormally high Th1 and CD8+ T lymphocyte responses, respectively. Collectively, these results reveal a novel and unexpected function for beta-catenin in programming DC differentiation toward subsets that orchestrate proinflammatory immunity to infection.

Immunity in the spleen and blood of mice immunized with irradiated Toxoplasma gondii tachyzoites

Toxoplasma gondii infection induces a strong and long-lasting immune response that is able to prevent most reinfections but allows tissue cysts. Irradiated, sterilized T. gondii tachyzoites are an interesting vaccine, and they induce immunity that is similar to infection, but without cysts. In this study, we evaluated the cellular immune response in the blood and spleen of mice immunized with this preparation by mouth (v.o.) or intraperitoneally (i.p.) and analyzed the protection after challenge with viable parasites. BALB/c mice were immunized with three i.p. or v.o. doses of irradiated T. gondii tachyzoites. Oral challenge with ten cysts of the ME-49 or VEG strain at 90 days after the last dose resulted in high levels of protection with low parasite burden in the immunized animals. There were higher levels of specific IgG, IgA and IgM antibodies in the serum, and the i.p. immunized mice had higher levels of the high-affinity IgG and IgM antibodies than the orally immunized mice, which had more high-affinity IgA antibodies. B cells (CD19(+)), plasma cells (CD138(+)) and the CD4(+) and CD8(+) T cell populations were increased in both the blood and spleen. Cells from the spleen of the i.p. immunized mice also showed antigen-induced production of interleukin-10 (IL-10), interferon gamma (IFN-γ) and interleukin 4 (IL-4). The CD4(+) T cells, B cells and likely CD8(+) T cells from the spleens of the i.p. immunized mice proliferated with a specific antigen. The protection was correlated with the spleen and blood CD8(+) T cell, high-affinity IgG and IgM and antigen-induced IL-10 and IL-4 production. Immunization with irradiated T. gondii tachyzoites induces an immune response that is mediated by B cells and CD4(+) and CD8(+) T cells, with increased humoral and cellular immune responses that are necessary for host protection after infection. The vaccine is similar to natural infection, but free of tissue cysts; this immunity restrains infection at challenge and can be an attractive and efficient model for vaccine development in toxoplasmosis.

Impact of Toxoplasma gondii on Dendritic Cell Subset Function in the Intestinal Mucosa

The function of mucosal dendritic cell (DC) subsets in immunity and inflammation is not well understood. In this study, we define four DC subsets present within the lamina propria and mesenteric lymph node compartments based on expression of CD103 and CD11b. Using IL-12p40 YFP (Yet40) reporter mice, we show that CD103(+)CD11b(-) mucosal DCs are primary in vivo sources of IL-12p40; we also identified CD103(-)CD11b(-) mucosal DCs as a novel population producing this cytokine. Infection was preferentially found in CD11b(+) DCs that were negative for CD103. Lamina propria DCs containing parasites were negative for IL-12p40. Instead, production of the cytokine was strictly a property of noninfected cells. We also show that vitamin A metabolism, as measured by ALDH activity, was preferentially found in CD103(+)CD11b(+) DC and was strongly downregulated in all mucosal DC subsets during infection. Finally, overall apoptosis of lamina propria DC subsets was increased during infection. Combined, these results highlight the ability of intestinal Toxoplasma infection to alter mucosal DC activity at both the whole population level and at the level of individual subsets.

An extrafollicular pathway for the generation of effector CD8(+) T cells driven by the proinflammatory cytokine, IL-12

The proinflammatory cytokine IL-12 drives the generation of terminally differentiated KLRG1⁺ effector CD8⁺ T cells. Using a Toxoplasma vaccination model, we delineate the sequence of events that naïve CD8⁺ T cells undergo to become terminal effectors and the differentiation steps controlled by IL-12. We demonstrate that direct IL-12 signaling on CD8⁺ T cells is essential for the induction of KLRG1 and IFN-γ, but the subsequent downregulation of CXCR3 is controlled by IL-12 indirectly through the actions of IFN-γ and IFN-γ-inducible chemokines. Differentiation of nascent effectors occurs in an extrafollicular splenic compartment and is driven by late IL-12 production by DCs distinct from the classical CD8α⁺ DC. Unexpectedly, we also found extensive proliferation of both KLRG1⁻ and KLRG1⁺ CD8⁺ T cells in the marginal zone and red pulp, which ceases prior to the final KLRG1^Hi CXCR3^Lo stage. Our findings highlight the notion of an extrafollicular pathway for effector T cell generation.

DOI:http://dx.doi.org/10.7554/eLife.09017.001

The immune system helps to protect us from cancer, infection by microbes and other diseases. There are several different types of immune cells that each have particular roles. For example, cytotoxic T cells can kill other cells in the body that are damaged or infected. These cells are found in various locations around the body—including a region of the spleen known as the white pulp—where they wait in an inactive state until they detect signals from a damaged or infected cell. These T cells divide and mature to produce populations of active T cells known as effector cytotoxic lymphoid cells (or CTLs for short), a process which is thought to occur within the white pulp.

A small protein called cytokine IL-12 is involved in the production of CTLs. The cytokine is released from other immune cells and causes the activated T cells to divide and mature. It has long been believed that IL-12 produced in the white pulp early on in the process is sufficient to drive this process, but more recent work suggests that sustained production of IL-12 in other areas of the spleen that are accessible to the bloodstream may be needed.

Here, Shah et al. studied the generation of cytotoxic T cells in mice that had been exposed to a vaccine against a disease called Toxoplasmosis. Their experiments show that IL-12 drives both the early and late stages of CTL production. In the early stages, the T cells respond to IL-12 that is secreted by a group of ‘lymphoid dendritic’ cells in the white pulp. However, in the later stages, the T cells move away from the white pulp to other parts of the spleen known as the marginal zone and red pulp, where a distinct group of ‘myeloid dendritic’ cells also produce IL-12 and direct the final maturation of the CTLs.

Shah et al.'s findings also show that the process in which cytotoxic T cells divide and later mature to produce CTLs involves a series of tightly controlled events that mostly occur outside of the white pulp. These observations provide a new perspective on how to develop vaccines and other treatments that more efficiently generate the CTLs needed to protect against infections and cancer.

DOI:http://dx.doi.org/10.7554/eLife.09017.002

CD8+ T cell immunity in an encephalitis model of Toxoplasma gondii infection

Toxoplasma gondii infection induces a robust CD8 T cell immunity in the infected host, which is critical for keeping chronic infection under control. IFNγ production and cytolytic activity exhibited by CD8 T cells are critical functions needed to prevent the reactivation of latent infection. Paradoxically, the susceptible mice infected with the parasite develop encephalitis irrespective of the presence of vigorous CD8 T cell immunity. Recent studies from our laboratory have demonstrated that these animals have defect in the memory CD8 T cell population, which become dysfunctional due to exhibition of inhibitory receptors like PD-1. Although the blockade of PD-1-PDL-1 pathway rescues the CD8 response, PD-1(hi) expressing cells are refractory to the treatment. In this review, we discuss the development of CD8 memory response during chronic infection, mechanism responsible for their dysfunctionality, and possible therapeutic measures that can be taken to reverse the process.

The CXCR3-CXCL11 signaling axis mediates macrophage recruitment and dissemination of mycobacterial infection

The recruitment of leukocytes to infectious foci depends strongly on the local release of chemoattractant mediators. The human CXC chemokine receptor 3 (CXCR3) is an important node in the chemokine signaling network and is expressed by multiple leukocyte lineages, including T cells and macrophages. The ligands of this receptor originate from an ancestral CXCL11 gene in early vertebrates. Here, we used the optically accessible zebrafish embryo model to explore the function of the CXCR3-CXCL11 axis in macrophage recruitment and show that disruption of this axis increases the resistance to mycobacterial infection. In a mutant of the zebrafish ortholog of CXCR3 (cxcr3.2), macrophage chemotaxis to bacterial infections was attenuated, although migration to infection-independent stimuli was unaffected. Additionally, attenuation of macrophage recruitment to infection could be mimicked by treatment with NBI74330, a high-affinity antagonist of CXCR3. We identified two infection-inducible CXCL11-like chemokines as the functional ligands of Cxcr3.2, showing that the recombinant proteins exerted a Cxcr3.2-dependent chemoattraction when locally administrated in vivo. During infection of zebrafish embryos with Mycobacterium marinum, a well-established model for tuberculosis, we found that Cxcr3.2 deficiency limited the macrophage-mediated dissemination of mycobacteria. Furthermore, the loss of Cxcr3.2 function attenuated the formation of granulomatous lesions, the typical histopathological features of tuberculosis, and led to a reduction in the total bacterial burden. Prevention of mycobacterial dissemination by targeting the CXCR3 pathway, therefore, might represent a host-directed therapeutic strategy for treatment of tuberculosis. The demonstration of a conserved CXCR3-CXCL11 signaling axis in zebrafish extends the translational applicability of this model for studying diseases involving the innate immune system.

Diverse roles for T-bet in the effector responses required for resistance to infection

The transcription factor T-bet has been most prominently linked to NK and T cell production of IFN-γ, a cytokine required for the control of a diverse array of intracellular pathogens. Indeed, in mice challenged with the parasite Toxoplasma gondii, NK and T cell responses are characterized by marked increases of T-bet expression. Unexpectedly, T-bet(-/-) mice infected with T. gondii develop a strong NK cell IFN-γ response that controls parasite replication at the challenge site, but display high parasite burdens at secondary sites colonized by T. gondii and succumb to infection. The loss of T-bet had a modest effect on T cell production of IFN-γ but did not impact on the generation of parasite-specific T cells. However, the absence of T-bet resulted in lower T cell expression of CD11a, Ly6C, KLRG-1, and CXCR3 and fewer parasite-specific T cells at secondary sites of infection, associated with a defect in parasite control at these sites. Together, these data highlight T-bet-independent pathways to IFN-γ production and reveal a novel role for this transcription factor in coordinating the T cell responses necessary to control this infection in peripheral tissues.

Transgenic expression of CXCR3 on T cells enhances susceptibility to cutaneous Leishmania major infection by inhibiting monocyte maturation and promoting a Th2 response

Cutaneous leishmaniasis, caused mainly by Leishmania major, an obligate intracellular parasite, is a disfiguring disease characterized by large skin lesions and is transmitted by a sand fly vector. We previously showed that the chemokine receptor CXCR3 plays a critical role in mediating resistance to cutaneous leishmaniasis caused by Leishmania major. Furthermore, T cells from L. major-susceptible BALB/c but not L. major-resistant C57BL/6 mice fail to efficiently upregulate CXCR3 upon activation. We therefore examined whether transgenic expression of CXCR3 on T cells would enhance resistance to L. major infection in susceptible BALB/c mice. We generated BALB/c and C57BL/6 transgenic mice, which constitutively overexpressed CXCR3 under a CD2 promoter, and then examined the outcomes with L. major infection. Contrary to our hypothesis, transgenic expression of CXCR3 (CXCR3(Tg)) on T cells of BALB/c mice resulted in increased lesion sizes and parasite burdens compared to wild-type (WT) littermates after L. major infection. Restimulated lymph node cells from L. major-infected BALB/c-CXCR3(Tg) mice produced more interleukin-4 (IL-4) and IL-10 and less gamma interferon (IFN-γ). Cells in draining lymph nodes from BALB/c-CXCR3(Tg) mice showed enhanced Th2 and reduced Th1 cell accumulation associated with increased neutrophils and inflammatory monocytes. However, monocytes displayed an immature phenotype which correlated with increased parasite burdens. Interestingly, transgenic expression of CXCR3 on T cells did not impact the outcome of L. major infection in C57BL/6 mice, which mounted a predominantly Th1 response and spontaneously resolved their infection similar to WT littermates. Our findings demonstrate that transgenic expression of CXCR3 on T cells increases susceptibility of BALB/c mice to L. major.

CXCL9 is important for recruiting immune T cells into the brain and inducing an accumulation of the T cells to the areas of tachyzoite proliferation to prevent reactivation of chronic cerebral infection with Toxoplasma gondii

T cells are required to maintain the latency of chronic infection with Toxoplasma gondii in the brain. Here, we examined the role of non-glutamic acid-leucine-arginine CXC chemokine CXCL9 for T-cell recruitment to prevent reactivation of infection with T. gondii. Severe combined immunodeficient (SCID) mice were infected and treated with sulfadiazine to establish a chronic infection. Immune T cells from infected wild-type mice were transferred into the SCID mice in combination with treatment with anti-CXCL9 or control sera. Three days later, sulfadiazine was discontinued to initiate reactivation of infection. Numbers of CD4(+) and CD8(+) T cells isolated from the brains were markedly less in mice treated with anti-CXCL9 serum than in mice treated with control serum at 3 days after sulfadiazine discontinuation. Amounts of tachyzoite (acute stage form of T. gondii)-specific SAG1 mRNA and numbers of foci associated with tachyzoites were significantly greater in the former than the latter at 5 days after sulfadiazine discontinuation. An accumulation of CD3(+) T cells into the areas of tachyzoite growth was significantly less frequent in the SCID mice treated with anti-CXCL9 serum than in mice treated with control serum. These results indicate that CXCL9 is crucial for recruiting immune T cells into the brain and inducing an accumulation of the T cells into the areas where tachyzoites proliferate to prevent reactivation of chronic T. gondii infection.

Effects of developmental activation of the AhR on CD4+ T-cell responses to influenza virus infection in adult mice

BACKGROUND

Epidemiological and animal studies indicate that maternal exposure to pollutants that bind the aryl hydrocarbon receptor (AhR) correlates with poorer ability to combat respiratory infection and lower antibody levels in the offspring. These observations point to an impact on CD4+ T cells. Yet, the consequence of developmental exposure to AhR ligands on the activation and differentiation of CD4+ T cells has not been directly examined.

OBJECTIVES

Our goal was to determine whether maternal exposure to an AhR ligand directly alters CD4+ T cell differentiation and function later in life.

METHODS

C57BL/6 mice were exposed to a prototypical AhR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), in utero and via suckling. We then measured CD4+ T-cell activation and differentiation into distinct effector populations in adult offspring that were infected with influenza A virus (IAV). Reciprocal adoptive transfers were used to define whether modifications in CD4+ T-cell responses resulted from direct effects of developmental TCDD exposure on CD4+ T cells.

RESULTS

Developmental exposure skewed CD4+ T-cell responses to IAV infection. We observed fewer virus-specific, activated CD4+ T cells and a reduced frequency of conventional CD4+ effector-cell subsets. However, there was an increase in regulatory CD4+ T cells. Direct effects of AhR activation on CD4+ T cells resulted in impaired differentiation into conventional effector subsets; this defect was transferred to mice that had not been developmentally exposed to TCDD.

CONCLUSIONS

Maternal exposure to TCDD resulted in durable changes in the responsive capacity and differentiation of CD4+ T cells in adult C57BL/6 mice.

The plasticity of inflammatory monocyte responses to the inflamed central nervous system

Over the last three decades it has become increasingly clear that monocytes, originally thought to have fixed, stereotypic responses to foreign stimuli, mediate exquisitely balanced protective and pathogenic roles in disease and immunity. This balance is crucial in core functional organs, such as the central nervous system (CNS), where minor changes in neuronal microenvironments and the production of immune factors can result in significant disease with fatal consequences or permanent neurological sequelae. Viral encephalitis and multiple sclerosis are examples of important human diseases in which the pathogenic contribution of monocytes recruited from the bone marrow plays a critical role in the clinical expression of disease, as they differentiate into macrophage or dendritic cells in the CNS to carry out effector functions. While antigen-specific lymphocyte populations are central to the adaptive immune response in both cases, in viral encephalitis a prominent macrophage infiltration may mediate immunopathological damage, seizure induction, and death. However, the autoimmune response to non-replicating, non-infectious, but abundant, self antigen has a different disease progression, associated with differentiation of significant numbers of infiltrating monocytes into dendritic cells in the CNS. Whilst a predominant presence of macrophages or dendritic cells in the inflamed CNS in viral encephalitis or multiple sclerosis is well described, the way in which the inflamed CNS mobilizes monocytes in the bone marrow to migrate to the CNS and the key drivers that lead to these specific differentiation pathways in vivo are not well understood. Here we review the current understanding of factors facilitating inflammatory monocyte generation, migration and entry into the brain, as well as their differentiation towards macrophages or dendritic cells in viral and autoimmune disease in relation to their respective disease outcomes.

The role of CXCR3 in DSS-induced colitis

Inflammatory bowel disease (IBD) is a group of disorders that are characterized by chronic, uncontrolled inflammation in the intestinal mucosa. Although the aetiopathogenesis is poorly understood, it is widely believed that IBD stems from a dysregulated immune response towards otherwise harmless commensal bacteria. Chemokines induce and enhance inflammation through their involvement in cellular trafficking. Reducing or limiting the influx of these proinflammatory cells has previously been demonstrated to attenuate inflammation. CXCR3, a chemokine receptor in the CXC family that binds to CXCL9, CXCL10 and CXCL11, is strongly overexpressed in the intestinal mucosa of IBD patients. We hypothesised that CXCR3 KO mice would have impaired cellular trafficking, thereby reducing the inflammatory insult by proinflammatory cell and attenuating the course of colitis. To investigate the role of CXCR3 in the progression of colitis, the development of dextran sulfate sodium (DSS)-induced colitis was investigated in CXCR3^−/− mice over 9 days. This study demonstrated attenuated DSS-induced colitis in CXCR3^−/− mice at both the macroscopic and microscopic level. Reduced colitis correlated with lower recruitment of neutrophils (p = 0.0018), as well as decreased production of IL-6 (p<0.0001), TNF (p = 0.0038), and IFN-γ (p = 0.0478). Overall, our results suggest that CXCR3 plays an important role in recruiting proinflammatory cells to the colon during colitis and that CXCR3 may be a therapeutic target to reduce the influx of proinflammatory cells in the inflamed colon.

Border maneuvers: deployment of mucosal immune defenses against Toxoplasma gondii

Toxoplasma gondii is a highly prevalent protozoan pathogen that is transmitted through oral ingestion of infectious cysts. As such, mucosal immune defenses in the intestine constitute the first and arguably most important line of resistance against the parasite. The response to infection is now understood to involve complex three-way interactions between Toxoplasma, the mucosal immune system, and the host intestinal microbiota. Productive outcome of these interactions ensures resolution of infection in the intestinal mucosa. Nonsuccessful outcome may result in emergence of proinflammatory damage that can spell death for the host. Here, we discuss new advances in our understanding of the mechanisms underpinning these disparate outcomes, with particular reference to initiators, effectors, and regulators of mucosal immunity stimulated by Toxoplasma in the intestine.

Complex immune cell interplay in the gamma interferon response during Toxoplasma gondii infection

Toxoplasma gondii is an obligate intracellular parasite of clinical importance, especially in immunocompromised patients. Investigations into the immune response to the parasite found that T cells are the primary effector cells regulating gamma interferon (IFN-γ)-mediated host resistance. However, recent studies have revealed a critical role for the innate immune system in mediating host defense independently of the T cell responses to the parasite. This body of knowledge is put into perspective by the unifying theme that immunity to the protozoan parasite requires a strong IFN-γ host response. In the following review, we discuss the role of IFN-γ-producing cells and the signals that regulate IFN-γ production during T. gondii infection.

Role of Chemokines and Trafficking of Immune Cells in Parasitic Infections

Parasites are diverse eukaryotic pathogens that can have complex life cycles. Their clearance, or control within a mammalian host requires the coordinated effort of the immune system. The cell types recruited to areas of infection can combat the disease, promote parasite replication and survival, or contribute to disease pathology. Location and timing of cell recruitment can be crucial. In this review, we explore the role chemokines play in orchestrating and balancing the immune response to achieve optimal control of parasite replication without promoting pathology.