The WT hemochromatosis protein HFE inhibits CD8⁺ T-lymphocyte activation

Species-specific responses during Seoul orthohantavirus infection in human and rat lung microvascular endothelial cells

Seoul orthohantavirus (SEOV) is a rat-borne zoonotic virus that is transmitted via inhalation of aerosolized infectious excreta, and can cause hemorrhagic fever with renal syndrome (HFRS) in humans worldwide. In rats, SEOV predominantly exists as a persistent infection in the absence of overt clinical signs. Lack of disease in rats is attributed to downregulation of pro-inflammatory and upregulation of regulatory host responses. As lung microvascular endothelial cells (LMECs) represent a primary target of infection in both human and rats, infections in these cells provide a unique opportunity to study the central role of LMECs in the dichotomy between pathogenicity in both species. In this study, host responses to SEOV infection in primary human and rat LMECs were directly compared on a transcriptional level. As infection of rat LMECs was more efficient than human LMECs, the majority of anti-viral defense responses were observed earlier in rat LMECs. Most prominently, SEOV-induced processes in both species included responses to cytokine stimulus, negative regulation of innate immune responses, responses to type I and II interferons, regulation of pattern recognition receptor signaling and MHC-I signaling. However, over time, in the rat LMECs, responses shifted from an anti-viral state towards a more immunotolerant state displayed by a PD-L1, B2M-, JAK2-focused interaction network aiding in negative regulation of cytotoxic CD8-positive T cell activation. This suggests a novel mechanism by which species-specific orthohantavirus-induced endothelium and T cell crosstalk may play a crucial role in the development of acute disease in humans and persistence in rodents.

An HIV elite controller patient carrying the homozygous H63D variant in the homeostatic iron regulator gene: A case report

RATIONALE

HIV elite controllers represent a rare subset of persons living with HIV, able to spontaneously control viral replication without antiviral therapy. HLA-B∗57 and HLA-B∗27 alleles are associated to efficient polyfunctional CD8+ T-cell response and are overrepresented in elite controllers but these alleles alone incompletely explain spontaneous HIV replication control in these subjects. Further mechanisms involved in innate and adaptive immune response and host genetics may contribute to this control. In this context, the homeostatic iron regulator (HFE) gene encodes a major histocompatibility complex-class-I-like molecule involved in both innate immunity, acting also through autophagy regulation, and iron homeostasis, strictly related to immune functions and susceptibility to infections.

PATIENT CONCERNS

Homozygousity for the p.His63Asp (H63D) variant in the HFE gene was identified in an 80-year-old HIV-infected woman with spontaneous control of viral replication.

DIAGNOSIS

HIV-1 RNA was undetectable in patient's serum with a routine assay and an ultra-sensitive assay (<1 copy/mL) during the 30 years follow-up. CD4+ and CD8+ T cell counts were stable and normal during all this period.

INTERVENTIONS

The patient had a history of absence of any physical ailment and no antiviral therapy has been prescribed during the 30 years of follow-up. The subject did not harbor HLA-B∗57 and HLA-B∗27 alleles. HFE gene was sequenced by Sanger, as part of a larger study on a cohort of HIV infected patients, aged >65 years and screened for polymorphisms in genes belonging to several pathways involved in neuroinflammation.

OUTCOMES

The woman had CD4+ and CD8+ T cell normal values and spontaneously controlled serum HIV-1 RNA levels for 30 years.

LESSONS

We assume that the interplay between the HFE H63D variant in homozygosity and innate immunity, perhaps through autophagy regulation, could play a role in HIV-1 replication control in our patient. This hypothesis needs to be explored in in vitro and in vivo studies. Understanding mechanisms involved in spontaneous control of HIV-1 replication remains indeed a challenge due to its possible implications for HIV cure research.

Cytokine and Gene Expression Profiling in Patients with HFE-Associated Hereditary Hemochromatosis according to Genetic Profile

BACKGROUND

Hemochromatosis gene (HFE)-associated hereditary hemochromatosis (HH) is characterized by downregulation of hepcidin synthesis, leading to increased intestinal iron absorption.

OBJECTIVES

The objectives were to characterize and elucidate a possible association between gene expression profile, hepcidin levels, disease severity, and markers of inflammation in HFE-associated HH patients.

METHODS

Thirty-nine HFE-associated HH patients were recruited and assigned to 2 groups according to genetic profile: C282Y homozygotes in 1 group and patients with H63D, as homozygote or in combination with C282Y, in the other group. Eleven healthy first-time blood donors were recruited as controls. Gene expression was characterized from peripheral blood cells, and inflammatory cytokines and hepcidin-25 isoform were quantified in serum. Biochemical disease characteristics were recorded.

RESULTS

Elevated levels of interleukin 8 were observed in a significant higher proportion of patients than controls. In addition, compared to controls, gene expression of ζ-globin was significantly increased among C282Y homozygote patients, while gene expression of matrix metalloproteinase 8, and other neutrophil-secreted proteins, was significantly upregulated in patients with H63D.

CONCLUSION

Different disease signatures may characterize HH patients according to their HFE genetic profile. Studies on larger populations, including analyses at protein level, are necessary to confirm these findings.

Iron in infection and immunity

Iron is an essential micronutrient for virtually all living cells. In infectious diseases, both invading pathogens and mammalian cells including those of the immune system require iron to sustain their function, metabolism and proliferation. On the one hand, microbial iron uptake is linked to the virulence of most human pathogens. On the other hand, the sequestration of iron from bacteria and other microorganisms is an efficient strategy of host defense in line with the principles of 'nutritional immunity'. In an acute infection, host-driven iron withdrawal inhibits the growth of pathogens. Chronic immune activation due to persistent infection, autoimmune disease or malignancy however, sequesters iron not only from infectious agents, autoreactive lymphocytes and neoplastic cells but also from erythroid progenitors. This is one of the key mechanisms which collectively result in the anemia of chronic inflammation. In this review, we highlight the most important interconnections between iron metabolism and immunity, focusing on host defense against relevant infections and on the clinical consequences of anemia of inflammation.

Methylation regulation of Antiviral host factors, Interferon Stimulated Genes (ISGs) and T-cell responses associated with natural HIV control

GWAS, immune analyses and biomarker screenings have identified host factors associated with in vivo HIV-1 control. However, there is a gap in the knowledge about the mechanisms that regulate the expression of such host factors. Here, we aimed to assess DNA methylation impact on host genome in natural HIV-1 control. To this end, whole DNA methylome in 70 untreated HIV-1 infected individuals with either high (>50,000 HIV-1-RNA copies/ml, n = 29) or low (<10,000 HIV-1-RNA copies/ml, n = 41) plasma viral load (pVL) levels were compared and identified 2,649 differentially methylated positions (DMPs). Of these, a classification random forest model selected 55 DMPs that correlated with virologic (pVL and proviral levels) and HIV-1 specific adaptive immunity parameters (IFNg-T cell responses and neutralizing antibodies capacity). Then, cluster and functional analyses identified two DMP clusters: cluster 1 contained hypo-methylated genes involved in antiviral and interferon response (e.g. PARP9, MX1, and USP18) in individuals with high viral loads while in cluster 2, genes related to T follicular helper cell (Tfh) commitment (e.g. CXCR5 and TCF7) were hyper-methylated in the same group of individuals with uncontrolled infection. For selected genes, mRNA levels negatively correlated with DNA methylation, confirming an epigenetic regulation of gene expression. Further, these gene expression signatures were also confirmed in early and chronic stages of infection, including untreated, cART treated and elite controllers HIV-1 infected individuals (n = 37). These data provide the first evidence that host genes critically involved in immune control of the virus are under methylation regulation in HIV-1 infection. These insights may offer new opportunities to identify novel mechanisms of in vivo virus control and may prove crucial for the development of future therapeutic interventions aimed at HIV-1 cure.

Iron Metabolism in Cancer Progression

Iron is indispensable for cell metabolism of both normal and cancer cells. In the latter, several disruptions of its metabolism occur at the steps of tumor initiation, progression and metastasis. Noticeably, cancer cells require a large amount of iron, and exhibit a strong dependence on it for their proliferation. Numerous iron metabolism-related proteins and signaling pathways are altered by iron in malignancies, displaying the pivotal role of iron in cancer. Iron homeostasis is regulated at several levels, from absorption by enterocytes to recycling by macrophages and storage in hepatocytes. Mutations in HFE gene alter iron homeostasis leading to hereditary hemochromatosis and to an increased cancer risk because the accumulation of iron induces oxidative DNA damage and free radical activity. Additionally, the iron capability to modulate immune responses is pivotal in cancer progression. Macrophages show an iron release phenotype and potentially deliver iron to cancer cells, resulting in tumor promotion. Overall, alterations in iron metabolism are among the metabolic and immunological hallmarks of cancer, and further studies are required to dissect how perturbations of this element relate to tumor development and progression.

Sexually dimorphic impact of the iron-regulating gene, HFE, on survival in glioblastoma

Background

The median survival for patients with glioblastoma (GBM), the most common primary malignant brain tumor in adults, has remained approximately 1 year for more than 2 decades. Recent advances in the field have identified GBM as a sexually dimorphic disease. It is less prevalent in females and they have better survival compared to males. The molecular mechanism of this difference has not yet been established. Iron is essential for many biological processes supporting tumor growth and its regulation is impacted by sex. Therefore, we interrogated the expression of a key component of cellular iron regulation, the HFE (homeostatic iron regulatory) gene, on sexually dimorphic survival in GBM.

Methods

We analyzed TCGA microarray gene expression and clinical data of all primary GBM patients (IDH-wild type) to compare tumor mRNA expression of HFE with overall survival, stratified by sex.

Results

In low HFE expressing tumors (below median expression, n = 220), survival is modulated by both sex and MGMT status, with the combination of female sex and MGMT methylation resulting in over a 10-month survival advantage (P < .0001) over the other groups. Alternatively, expression of HFE above the median (high HFE, n = 240) is associated with significantly worse overall survival in GBM, regardless of MGMT methylation status or patient sex. Gene expression analysis uncovered a correlation between high HFE expression and expression of genes associated with immune function.

Conclusions

The level of HFE expression in GBM has a sexually dimorphic impact on survival. Whereas HFE expression below the median imparts a survival benefit to females, high HFE expression is associated with significantly worse overall survival regardless of established prognostic factors such as sex or MGMT methylation.

Development and Validation of an IDH1-Associated Immune Prognostic Signature for Diffuse Lower-Grade Glioma

A mutation in the isocitrate dehydrogenase 1 (IDH1) gene is the most common mutation in diffuse lower-grade gliomas (LGGs), and it is significantly related to the prognosis of LGGs. We aimed to explore the influence of the IDH1 mutation on the immune microenvironment and develop an IDH1-associated immune prognostic signature (IPS) for predicting prognosis in LGGs. IDH1 mutation status and RNA expression were investigated in two different public cohorts. To develop an IPS, LASSO Cox analysis was conducted for immune-related genes that were differentially expressed between IDH1^wt and IDH1^mut LGG patients. Then, we systematically analyzed the influence of the IPS on the immune microenvironment. A total of 41 immune prognostic genes were identified based on the IDH1 mutation status. A four-gene IPS was established and LGG patients were effectively stratified into low- and high-risk groups in both the training and validation sets. Stratification analysis and multivariate Cox analysis revealed that the IPS was an independent prognostic factor. We also found that high-risk LGG patients had higher levels of infiltrating B cells, CD4+ T cells, CD8+ T cells, neutrophils, macrophages and dendritic cells, and expressed higher levels of CTLA-4, PD-1 and TIM-3. Moreover, a novel nomogram model was established to estimate the overall survival in LGG patients. The current study provides novel insights into the LGG immune microenvironment and potential immunotherapies. The proposed IPS is a clinically promising biomarker that can be used to classify LGG patients into subgroups with distinct outcomes and immunophenotypes, with the potential to facilitate individualized management and improve prognosis.

Increased Plasma Ferritin Concentration and Low-Grade Inflammation-A Mendelian Randomization Study

BACKGROUND

It is unknown why increased plasma ferritin concentration predicts all-cause mortality. As low-grade inflammation and increased plasma ferritin concentration are associated with all-cause mortality, we hypothesized that increased plasma ferritin concentration is genetically associated with low-grade inflammation.

METHODS

We investigated whether increased plasma ferritin concentration is associated with low-grade inflammation [i.e., increased concentrations of C-reactive protein (CRP) and complement component 3 (C3)] in 62537 individuals from the Danish general population. We also applied a Mendelian randomization approach, using the hemochromatosis genotype C282Y/C282Y as an instrument for increased plasma ferritin concentration, to assess causality.

RESULTS

For a doubling in plasma ferritin concentration, the odds ratio (95% CI) for CRP ≥2 vs <2 mg/L was 1.12 (1.09-1.16), with a corresponding genetic estimate for C282Y/C282Y of 1.03 (1.01-1.06). For a doubling in plasma ferritin concentration, odds ratio (95% CI) for complement C3 >1.04 vs ≤1.04 g/L was 1.28 (1.21-1.35), and the corresponding genetic estimate for C282Y/C282Y was 1.06 (1.03-1.12). Mediation analyses showed that 74% (95% CI, 24-123) of the association of C282Y/C282Y with risk of increased CRP and 56% (17%-96%) of the association of C282Y/C282Y with risk of increased complement C3 were mediated through plasma ferritin concentration.

CONCLUSIONS

Increased plasma ferritin concentration as a marker of increased iron concentration is associated observationally and genetically with low-grade inflammation, possibly indicating a causal relationship from increased ferritin to inflammation. However, as HFE may also play an immunological role indicating pleiotropy and as incomplete penetrance of C282Y/C282Y indicates buffering mechanisms, these weaknesses in the study design could bias the genetic estimates.

Human Leukocyte Antigen (HLA) and Immune Regulation: How Do Classical and Non-Classical HLA Alleles Modulate Immune Response to Human Immunodeficiency Virus and Hepatitis C Virus Infections?

The genetic factors associated with susceptibility or resistance to viral infections are likely to involve a sophisticated array of immune response. These genetic elements may modulate other biological factors that account for significant influence on the gene expression and/or protein function in the host. Among them, the role of the major histocompatibility complex in viral pathogenesis in particular human immunodeficiency virus (HIV) and hepatitis C virus (HCV), is very well documented. We, recently, added a novel insight into the field by identifying the molecular mechanism associated with the protective role of human leukocyte antigen (HLA)-B27/B57 CD8⁺ T cells in the context of HIV-1 infection and why these alleles act as a double-edged sword protecting against viral infections but predisposing the host to autoimmune diseases. The focus of this review will be reexamining the role of classical and non-classical HLA alleles, including class Ia (HLA-A, -B, -C), class Ib (HLA-E, -F, -G, -H), and class II (HLA-DR, -DQ, -DM, and -DP) in immune regulation and viral pathogenesis (e.g., HIV and HCV). To our knowledge, this is the very first review of its kind to comprehensively analyze the role of these molecules in immune regulation associated with chronic viral infections.

The hemochromatosis protein HFE 20 years later: An emerging role in antigen presentation and in the immune system

Introduction

Since its discovery, the hemochromatosis protein HFE has been primarily defined by its role in iron metabolism and homeostasis, and its involvement in the genetic disease termed hereditary hemochromatosis (HH). While HH patients are typically afflicted by dysregulated iron levels, many are also affected by several immune defects and increased incidence of autoimmune diseases that have thereby implicated HFE in the immune response. Growing evidence has supported an immunological role for HFE with recent studies describing HFE specifically as it relates to MHC I antigen presentation.

Methods/Results

Here, we present a comprehensive overview of the relationship between iron metabolism, HFE, and the immune system to better understand the origin and cause of immune defects in HH patients. We further describe the role of HFE in MHC I antigen presentation and its potential to impair autoimmune responses in homeostatic conditions, a mechanism which may be exploited by tumors to evade immune surveillance.

Conclusion

Overall, this increased understanding of the role of HFE in the immune response sets the stage for better treatment and management of HH and other iron‐related diseases, as well as of the immune defects related to this condition.

The role of MHC class Ib-restricted T cells during infection

Even though major histocompatibility complex (MHC) class Ia and many Ib molecules have similarities in structure, MHC class Ib molecules tend to have more specialized functions, which include the presentation of non-peptidic antigens to non-classical T cells. Likewise, non-classical T cells also have unique characteristics, including an innate-like phenotype in naïve animals and rapid effector functions. In this review, we discuss the role of MAIT and NKT cells during infection but also the contribution of less studied MHC class Ib-restricted T cells such as Qa-1-, Qa-2-, and M3-restricted T cells. We focus on describing the types of antigens presented to non-classical T cells, their response and cytokine profile following infection, as well as the overall impact of these T cells to the immune system.

Lymphocyte gene expression signatures from patients and mouse models of hereditary hemochromatosis reveal a function of HFE as a negative regulator of CD8+ T-lymphocyte activation and differentiation in vivo

Abnormally low CD8⁺ T-lymphocyte numbers is characteristic of some patients with hereditary hemochromatosis (HH), a MHC-linked disorder of iron overload. Both environmental and genetic components are known to influence CD8⁺ T-lymphocyte homeostasis but the role of the HH associated protein HFE is still insufficiently understood. Genome-wide expression profiling was performed in peripheral blood CD8⁺ T lymphocytes from HH patients selected according to CD8⁺ T-lymphocyte numbers and from Hfe^-/- mice maintained either under normal or high iron diet conditions. In addition, T-lymphocyte apoptosis and cell cycle progression were analyzed by flow cytometry in HH patients. HH patients with low CD8⁺ T-lymphocyte numbers show a differential expression of genes related to lymphocyte differentiation and maturation namely CCR7, LEF1, ACTN1, NAA50, P2RY8 and FOSL2, whose expression correlates with the relative proportions of naïve, central and effector memory subsets. In addition, expression levels of LEF1 and P2RY8 in memory cells as well as the proportions of CD8⁺ T cells in G2/M cell cycle phase are significantly different in HH patients compared to controls. Hfe^-/- mice do not show alterations in CD8⁺ T-lymphocyte numbers but differential gene response patterns. We found an increased expression of S100a8 and S100a9 that is most pronounced in high iron diet conditions. Similarly, CD8⁺ T lymphocytes from HH patients display higher S100a9 expression both at the mRNA and protein level. Altogether, our results support a role for HFE as a negative regulator of CD8⁺ T-lymphocyte activation. While the activation markers S100a8 and S100a9 are strongly increased in CD8⁺ T cells from both, Hfe^-/- mice and HH patients, a differential profile of genes related to differentiation/maturation of CD8⁺ T memory cells is evident in HH patients only. This supports the notion that HFE contributes, at least in part, to the generation of low peripheral blood CD8⁺ T lymphocytes in HH.

T lymphocyte-derived TNF and IFN-γ repress HFE expression in cancer cells

The immune system and tumors are closely intertwined initially upon tumor development. During this period, tumors evolve to promote self-survival through immune escape, including by targeting crucial components involved in the presentation of antigens to the immune system in order to avoid recognition. Accordingly, components involved in MHC I presentation of tumor antigens are often mutated and down-regulated targets in tumors. On the other hand, the immune system has been shown to influence tumors through production of immunosuppressive cytokines, recruitment and polarization of cells favoring or impeding tumor escape or through production of anti-tumor cytokines promoting tumor rejection. We previously discovered that the hemochromatosis protein HFE, a negative regulator of iron absorption, dampens classical MHC I antigen presentation. In this study, we evaluated the impact of activated T lymphocytes purified from peripheral blood mononuclear cells (PBMC) on HFE expression in tumor cell lines. We co-cultured tumor cell lines from melanoma, lung, and kidney cancers with anti-CD3-activated PBMC and established that HFE expression is increased in tumor cell lines compared to healthy tissues, whilst being down-regulated significantly upon exposure to activated PBMC. HFE down-regulation was mediated by both CD4 and CD8 T lymphocytes, through production of soluble mediators, namely TNF and IFN-γ. These results suggest that the immune system may modulate tumor HFE expression in inflammatory conditions in order to regulate MHC I antigen presentation and promote tumor clearance.