Epigenetics and Trained Immunity

Primary and Memory Response of Human Monocytes to Vaccines: Role of Nanoparticulate Antigens in Inducing Innate Memory

Innate immune cells such as monocytes and macrophages are activated in response to microbial and other challenges and mount an inflammatory defensive response. Exposed cells develop the so-called innate memory, which allows them to react differently to a subsequent challenge, aiming at better protection. In this study, using human primary monocytes in vitro, we have assessed the memory-inducing capacity of two antigenic molecules of Schistosoma mansoni in soluble form compared to the same molecules coupled to outer membrane vesicles of Neisseria lactamica. The results show that particulate challenges are much more efficient than soluble molecules in inducing innate memory, which is measured as the production of inflammatory and anti-inflammatory cytokines (TNFα, IL-6, IL-10). Controls run with LPS from Klebsiella pneumoniae compared to the whole bacteria show that while LPS alone has strong memory-inducing capacity, the entire bacteria are more efficient. These data suggest that microbial antigens that are unable to induce innate immune activation can nevertheless participate in innate activation and memory when in a particulate form, which is a notion that supports the use of nanoparticulate antigens in vaccination strategies for achieving adjuvant-like effects of innate activation as well as priming for improved reactivity to future challenges.

Resolving trained immunity with systems biology

Trained immunity is characterized by long-term functional reprogramming of innate immune cells following challenge with pathogens or microbial ligands during infection or vaccination. This cellular reprogramming leads to increased responsiveness upon restimulation, and is mediated through epigenetic and metabolic modifications. In this review, we describe how molecular mechanisms underlying trained immunity, for example, induced by β-glucan or Bacille Calmette-Guérin (BCG) vaccination, can be investigated by using and integrating different layers of information including genome, epigenome, transcriptome, proteome, metabolome, microbiome, immune cell phenotyping, and function. We also describe the most commonly used experimental and computational techniques. Finally, we provide a number of examples of how a systems biology approach was applied to study trained immunity to understand interindividual variation or the complex interplay between molecular layers. In conclusion, trained immunity represents an opportunity for regulating innate immune function, and understanding the complex interplay of mechanisms that mediate trained immunity might enable us to employ it as a clinical tool in the future.

Trained Immunity and Reactivity of Macrophages and Endothelial Cells

Innate immune cells can develop exacerbated immunologic response and long-term inflammatory phenotype following brief exposure to endogenous or exogenous insults, which leads to an altered response towards a second challenge after the return to a nonactivated state. This phenomenon is known as trained immunity (TI). TI is not only important for host defense and vaccine response but also for chronic inflammations such as cardiovascular and metabolic diseases such as atherosclerosis. TI can occur in innate immune cells such as monocytes/macrophages, natural killer cells, endothelial cells (ECs), and nonimmune cells, such as fibroblast. In this brief review, we analyze the significance of TI in ECs, which are also considered as innate immune cells in addition to macrophages. TI can be induced by a variety of stimuli, including lipopolysaccharides, BCG (bacillus Calmette-Guerin), and oxLDL (oxidized low-density lipoprotein), which are defined as risk factors for cardiovascular and metabolic diseases. Furthermore, TI in ECs is functional for inflammation effectiveness and transition to chronic inflammation. Rewiring of cellular metabolism of the trained cells takes place during induction of TI, including increased glycolysis, glutaminolysis, increased accumulation of tricarboxylic acid cycle metabolites and acetyl-coenzyme A production, as well as increased mevalonate synthesis. Subsequently, this leads to epigenetic remodeling, resulting in important changes in chromatin architecture that enables increased gene transcription and enhanced proinflammatory immune response. However, TI pathways and inflammatory pathways are separated to ensure memory stays when inflammation undergoes resolution. Additionally, reactive oxygen species play context-dependent roles in TI. Therefore, TI plays significant roles in EC and macrophage pathology and chronic inflammation. However, further characterization of TI in ECs and macrophages would provide novel insights into cardiovascular disease pathogenesis and new therapeutic targets. Graphic Abstract: A graphic abstract is available for this article.

Innate and Adaptive Immunity in Giant Cell Arteritis

Autoimmune diseases can afflict every organ system, including blood vessels that are critically important for host survival. The most frequent autoimmune vasculitis is giant cell arteritis (GCA), which causes aggressive wall inflammation in medium and large arteries and results in vaso-occlusive wall remodeling. GCA shares with other autoimmune diseases that it occurs in genetically predisposed individuals, that females are at higher risk, and that environmental triggers are suspected to beget the loss of immunological tolerance. GCA has features that distinguish it from other autoimmune diseases and predict the need for tailored diagnostic and therapeutic approaches. At the core of GCA pathology are CD4⁺ T cells that gain access to the protected tissue niche of the vessel wall, differentiate into cytokine producers, attain tissue residency, and enforce macrophages differentiation into tissue-destructive effector cells. Several signaling pathways have been implicated in initiating and sustaining pathogenic CD4⁺ T cell function, including the NOTCH1-Jagged1 pathway, the CD28 co-stimulatory pathway, the PD-1/PD-L1 co-inhibitory pathway, and the JAK/STAT signaling pathway. Inadequacy of mechanisms that normally dampen immune responses, such as defective expression of the PD-L1 ligand and malfunction of immunosuppressive CD8⁺ T regulatory cells are a common theme in GCA immunopathology. Recent studies are providing a string of novel mechanisms that will permit more precise pathogenic modeling and therapeutic targeting in GCA and will fundamentally inform how abnormal immune responses in blood vessels lead to disease.

TLR Agonists as Mediators of Trained Immunity: Mechanistic Insight and Immunotherapeutic Potential to Combat Infection

Despite advances in critical care medicine, infection remains a significant problem that continues to be complicated with the challenge of antibiotic resistance. Immunocompromised patients are highly susceptible to development of severe infection which often progresses to the life-threatening condition of sepsis. Thus, immunotherapies aimed at boosting host immune defenses are highly attractive strategies to ward off infection and protect patients. Recently there has been mounting evidence that activation of the innate immune system can confer long-term functional reprogramming whereby innate leukocytes mount more robust responses upon secondary exposure to a pathogen for more efficient clearance and host protection, termed trained immunity. Toll-like receptor (TLR) agonists are a class of agents which have been shown to trigger the phenomenon of trained immunity through metabolic reprogramming and epigenetic modifications which drive profound augmentation of antimicrobial functions. Immunomodulatory TLR agonists are also highly beneficial as vaccine adjuvants. This review provides an overview on TLR signaling and our current understanding of TLR agonists which show promise as immunotherapeutic agents for combating infection. A brief discussion on our current understanding of underlying mechanisms is also provided. Although an evolving field, TLR agonists hold strong therapeutic potential as immunomodulators and merit further investigation for clinical translation.

Impact of BCG revaccination on the response to unrelated vaccines in a Ugandan adolescent birth cohort: randomised controlled trial protocol C for the 'POPulation differences in VACcine responses' (POPVAC) programme

INTRODUCTION

There is evidence that BCG immunisation may protect against unrelated infectious illnesses. This has led to the postulation that administering BCG before unrelated vaccines may enhance responses to these vaccines. This might also model effects of BCG on unrelated infections.

METHODS AND ANALYSIS

To test this hypothesis, we have designed a randomised controlled trial of BCG versus no BCG immunisation to determine the effect of BCG on subsequent unrelated vaccines, among 300 adolescents (aged 13-17 years) from a Ugandan birth cohort. Our schedule will comprise three main immunisation days (week 0, week 4 and week 28): BCG (or no BCG) revaccination at week 0; yellow fever (YF-17D), oral typhoid (Ty21a) and human papillomavirus (HPV) prime at week 4; and HPV boost and tetanus/diphtheria (Td) boost at week 28. Primary outcomes are anti-YF-17D neutralising antibody titres, Salmonella typhi lipopolysaccharide-specific IgG concentration, IgG specific for L1-proteins of HPV-16/HPV-18 and tetanus and diphtheria toxoid-specific IgG concentration, all assessed at 4 weeks after immunisation with YF, Ty21a, HPV and Td, respectively. Secondary analyses will determine effects on correlates of protective immunity (where recognised correlates exist), on vaccine response waning and on whether there are differential effects on priming versus boosting immunisations. We will also conduct exploratory immunology assays among subsets of participants to further characterise effects of BCG revaccination on vaccine responses. Further analyses will assess which life course exposures influence vaccine responses in adolescence.

ETHICS AND DISSEMINATION

Ethics approval has been obtained from relevant Ugandan and UK ethics committees. Results will be shared with Uganda Ministry of Health, relevant district councils, community leaders and study participants. Further dissemination will be done through conference proceedings and publications.

TRIAL REGISTRATION NUMBER

ISRCTN10482904.

Crosstalk Between Staphylococcus aureus and Innate Immunity: Focus on Immunometabolism

Staphylococcus aureus is a leading cause of bacterial infections globally in both healthcare and community settings. The success of this bacterium is the product of an expansive repertoire of virulence factors in combination with acquired antibiotic resistance and propensity for biofilm formation. S. aureus leverages these factors to adapt to and subvert the host immune response. With the burgeoning field of immunometabolism, it has become clear that the metabolic program of leukocytes dictates their inflammatory status and overall effectiveness in clearing an infection. The metabolic flexibility of S. aureus offers an inherent means by which the pathogen could manipulate the infection milieu to promote its survival. The exact metabolic pathways that S. aureus influences in leukocytes are not entirely understood, and more work is needed to understand how S. aureus co-opts leukocyte metabolism to gain an advantage. In this review, we discuss the current knowledge concerning how metabolic biases dictate the pro- vs. anti-inflammatory attributes of various innate immune populations, how S. aureus metabolism influences leukocyte activation, and compare this with other bacterial pathogens. A better understanding of the metabolic crosstalk between S. aureus and leukocytes may unveil novel therapeutic strategies to combat these devastating infections.

Tricarboxylic Acid (TCA) Cycle Intermediates: Regulators of Immune Responses

The tricarboxylic acid cycle (TCA) is a series of chemical reactions used in aerobic organisms to generate energy via the oxidation of acetylcoenzyme A (CoA) derived from carbohydrates, fatty acids and proteins. In the eukaryotic system, the TCA cycle occurs completely in mitochondria, while the intermediates of the TCA cycle are retained inside mitochondria due to their polarity and hydrophilicity. Under cell stress conditions, mitochondria can become disrupted and release their contents, which act as danger signals in the cytosol. Of note, the TCA cycle intermediates may also leak from dysfunctioning mitochondria and regulate cellular processes. Increasing evidence shows that the metabolites of the TCA cycle are substantially involved in the regulation of immune responses. In this review, we aimed to provide a comprehensive systematic overview of the molecular mechanisms of each TCA cycle intermediate that may play key roles in regulating cellular immunity in cell stress and discuss its implication for immune activation and suppression.

Trained innate immunity

The innate immune system acts rapidly in an identical and nonspecific way every time the body is exposed to pathogens. As such, it cannot build and maintain immunological memory to help prevent reinfection. Researchers contend that trained immunity is influenced by intracellular metabolic pathways and epigenetic remodeling. The purpose of this review was to explore the topic of trained innate immunity based on the results of relevant previous studies. This systematic review entailed identifying articles related to trained innate immunity. The sources were obtained from PubMed using different search terms that included "trained innate immunity," "trained immunity," "trained," "innate," "immunity," and "immune system." Boolean operators were used to combine terms and phrases. A review of previous study results revealed that little is currently known about the molecular and cellular processes that mediate or induce a trained immune response in animals. However, it is believed that alterations in the phenotypes of cell populations and the numbers of specific cells may play a critical role in mediating the trained immune response. Increasing evidence shows that the protective processes and actions that occur during a secondary infection are not entirely linked to the adaptive immune system. Instead, these events also involve heightened activation of innate immune cells. While trained innate immune cells may have a shorter memory, they assist in the fight against pathogens and provide cross-protection. Identification of the mechanisms and molecules that underlie trained innate immunity has highlighted important features of the human immune response. Such advances continue to open doors for future research on how the body responds to disease-causing pathogens.

Immune memory: an evolutionary perspective

The innate immune system, through pattern recognition receptors, intercepts any kind of pathogen and reacts through chemotactic, phagocyting, cytokines-secreting and cell-killing mechanisms in a very quick and effective way. Meanwhile, the adaptive immunity arm, through dendritic and T and B cells memory activation, is alerted and starts, more slowly, to produce antibodies, seen thanks to the progress of immunological investigations in comparative vertebrates, invertebrates, and vegetal models.However, it has been stated that the innate immune system also displays adaptive potential in terms of reinfection resistance through immune memory, in addition to the modulation of responses against repeated low doses of lipopolysaccharides (Lps) or cross-immunization, starting from one pathogenic species and extending to others.

Genome-Wide Histone Modifications and CTCF Enrichment Predict Gene Expression in Sheep Macrophages

Alveolar macrophages function in innate and adaptive immunity, wound healing, and homeostasis in the lungs dependent on tissue-specific gene expression under epigenetic regulation. The functional diversity of tissue resident macrophages, despite their common myeloid lineage, highlights the need to study tissue-specific regulatory elements that control gene expression. Increasing evidence supports the hypothesis that subtle genetic changes alter sheep macrophage response to important production pathogens and zoonoses, for example, viruses like small ruminant lentiviruses and bacteria like Coxiella burnetii. Annotation of transcriptional regulatory elements will aid researchers in identifying genetic mutations of immunological consequence. Here we report the first genome-wide survey of regulatory elements in any sheep immune cell, utilizing alveolar macrophages. We assayed histone modifications and CTCF enrichment by chromatin immunoprecipitation with deep sequencing (ChIP-seq) in two sheep to determine cis-regulatory DNA elements and chromatin domain boundaries that control immunity-related gene expression. Histone modifications included H3K4me3 (denoting active promoters), H3K27ac (active enhancers), H3K4me1 (primed and distal enhancers), and H3K27me3 (broad silencers). In total, we identified 248,674 reproducible regulatory elements, which allowed assignment of putative biological function in macrophages to 12% of the sheep genome. Data exceeded the FAANG and ENCODE standards of 20 million and 45 million useable fragments for narrow and broad marks, respectively. Active elements showed consensus with RNA-seq data and were predictive of gene expression in alveolar macrophages from the publicly available Sheep Gene Expression Atlas. Silencer elements were not enriched for expressed genes, but rather for repressed developmental genes. CTCF enrichment enabled identification of 11,000 chromatin domains with mean size of 258 kb. To our knowledge, this is the first report to use immunoprecipitated CTCF to determine putative topological domains in sheep immune cells. Furthermore, these data will empower phenotype-associated mutation discovery since most causal variants are within regulatory elements.

Targeting Impaired Antimicrobial Immunity in the Brain for the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia and aging is the most common risk factor for developing the disease. The etiology of AD is not known but AD may be considered as a clinical syndrome with multiple causal pathways contributing to it. The amyloid cascade hypothesis, claiming that excess production or reduced clearance of amyloid-beta (Aβ) and its aggregation into amyloid plaques, was accepted for a long time as the main cause of AD. However, many studies showed that Aβ is a frequent consequence of many challenges/pathologic processes occurring in the brain for decades. A key factor, sustained by experimental data, is that low-grade infection leading to production and deposition of Aβ, which has antimicrobial activity, precedes the development of clinically apparent AD. This infection is chronic, low grade, largely clinically silent for decades because of a nearly efficient antimicrobial immune response in the brain. A chronic inflammatory state is induced that results in neurodegeneration. Interventions that appear to prevent, retard or mitigate the development of AD also appear to modify the disease. In this review, we conceptualize further that the changes in the brain antimicrobial immune response during aging and especially in AD sufferers serve as a foundation that could lead to improved treatment strategies for preventing or decreasing the progression of AD in a disease-modifying treatment.

Microglial innate memory and epigenetic reprogramming in neurological disorders

Microglia are myeloid-derived cells recognized as brain-resident macrophages. They act as the first and main line of immune defense in the central nervous system (CNS). Microglia have high phenotypic plasticity and are essential for regulating healthy brain homeostasis, and their dysregulation underlies the onset and progression of several CNS pathologies through impaired inflammatory responses. Aberrant microglial activation, following an inflammatory insult, is associated with epigenetic dysregulation in various CNS pathologies. Emerging data suggest that certain stimuli to myeloid cells determine enhanced or attenuated responses to subsequent stimuli. These phenomena, generally termed innate immune memory (IIM), are highly dependent on epigenetic reprogramming. Microglial priming has been reported in several neurological diseases and corresponds to a state of increased permissiveness or exacerbated response, promoted by continuous exposure to a chronic pro-inflammatory environment. In this article, we provide extensive evidence of these epigenetic-mediated phenomena under neurological conditions and discuss their contribution to pathogenesis and their clinical implications, including those concerning potential novel therapeutic approaches.

Overcoming immune dysfunction in the elderly: trained immunity as a novel approach

People with advanced age have a higher susceptibility to infections and exhibit increased mortality and morbidity as the ability of the immune system to combat infections decreases with age. While innate immune cells display functional defects such as decreased phagocytosis, chemotaxis and cytokine production, adaptive immune cells exhibit reduced receptor diversity, defective antibody production and a sharp decline in naive cell populations. Successful responses to vaccination in the elderly are critical to prevent common infections such as influenza and pneumonia, but vaccine efficacy decreases in older individuals compared with young adults. Trained immunity is a newly emerging concept that showed that innate immune cells possess non-specific immunological memory established through epigenetic and metabolic reprogramming upon encountering certain pathogenic stimuli. Clinical studies suggest that trained immunity can be utilized to enhance immune responses against infections and improve the efficiency of vaccinations in adults; however, how trained immunity responses are shaped with advanced age is still an open question. In this review, we provide an overview of the age-related changes in the immune system with a focus on innate immunity, discuss current vaccination strategies for the elderly, present the concept of trained immunity and propose it as a novel approach to enhance responses against infections and vaccinations in the elderly population.

Microalgal extracts induce larval programming and modify growth and the immune response to bioactive treatments and LCDV in Senegalese sole post-larvae

Immunostimulants are key molecules in aquaculture since they heighten defensive responses and protection against pathogens. The present study investigated the treatment of Senegalese sole larvae with a whole-cell crude extract of the microalgae Nannochloropsis gaditana (Nanno) and programming of growth and the immune system. Larvae at hatch were treated with the Nanno extracts for 2 h and thereafter were cultivated for 32 days post-hatch (dph) in parallel with an untreated control group (CN). Dry weight and length at 21 days post-hatch (dph) were higher in post-larvae of the Nanno than CN group. These differences in weight were later confirmed at 32 dph. To evaluate changes in the immune response associated with Nanno-programming treatments, the Nanno and CN post-larvae were supplied with two bioactive compounds yeast β-glucan (Y) and a microalga extract from the diatom Phaeodactylum tricornutum (MAe). The bioactive treatments were administrated to the treatment groups through the live prey (artemia metanauplii, 200 artemia mL^-1) enriched for 30 min with MAe or Y (at 2 mg mL^-1 SW) or untreated prey in the case of the negative control (SW). The effect of the treatments was assessed by monitoring gene expression, enzyme activity and mortality over 48 h. The post-larvae sole supplied with the bioactive compounds Y and MAe had increased mortality at 48 h compared to the SW group. Moreover, mortality was higher in Nanno-programmed than CN post-larvae. Lysozyme and total anti-protease enzymatic activities at 6 and 24 h after the start of the trial were significantly higher in the Nanno and MAe supplied post-larvae compared to their corresponding control (CN and SW, respectively). Immune gene transcripts revealed that il1b, cxc10 and mx mRNAs were significantly different between Nanno and CN post-larvae at 6 and 24 h. Moreover, the expression of il1b, tnfa, cxc10, irf3, irf7 and mx was modified by bioactive treatments but with temporal differences. At 48 h after bioactive treatments, Y and SW post-larvae were challenged with the lymphocystis disease virus (LCDV). No difference existed in viral copy number between programming or bioactive treatment groups at 3, 6 and 24 h after LCDV challenge although the total number of copies reduced with time. Gene expression profiles in the LCDV-challenged group indicated that post-larvae triggered a wide defensive response compared to SWC 24 h after challenge, which was modulated by programming and bioactive compound treatments. Cluster analysis of expressed genes separated the SW and Y groups indicating long-lasting effects of yeast β-glucan treatment in larvae. A noteworthy interaction between Nanno-programming and Y-treatment on the regulation of antiviral genes was observed. Overall, the data demonstrate the capacity of microalgal crude extracts to modify sole larval plasticity with long-term effects on larval growth and the immune responses.

Probing metabolic memory in the hepatic response to fasting

Tissues may respond differently to a particular stimulus if they have been previously exposed to that same stimulus. Here, we tested the hypothesis that a strong metabolic stimulus such as fasting may influence the hepatic response to a subsequent fast and thus elicit a memory effect. Overnight fasting in mice significantly increased plasma free fatty acids, glycerol, β-hydroxybutyrate, and liver triglycerides, and decreased plasma glucose, plasma triglycerides, and liver glycogen levels. In addition, fasting dramatically changed the liver transcriptome, upregulating genes involved in gluconeogenesis and in uptake, oxidation, storage, and mobilization of fatty acids, and downregulating genes involved in fatty acid synthesis, fatty acid elongation/desaturation, and cholesterol synthesis. Fasting also markedly impacted the liver metabolome, causing a decrease in the levels of numerous amino acids, glycolytic-intermediates, TCA cycle intermediates, and nucleotides. However, these fasting-induced changes were unaffected by two previous overnight fasts. Also, no significant effect was observed of prior fasting on glucose tolerance. Finally, analysis of the effect of fasting on the transcriptome in hepatocyte humanized mouse livers indicated modest similarity in gene regulation in mouse and human liver cells. In general, genes involved in metabolic pathways were upregulated or downregulated to a lesser extent in human liver cells than in mouse liver cells. In conclusion, we found that previous exposure to fasting in mice did not influence the hepatic response to a subsequent fast, arguing against the concept of metabolic memory in the liver. Our data provide a useful resource for the study of liver metabolism during fasting.

Central and local controls of monocytopoiesis influence the outcome of Leishmania infection

Leishmaniases represent a complex of tropical and subtropical diseases caused by an intracellular protozoon of the genus Leishmania. The principal cells controlling the interaction between the host and the parasite Leishmania are monocytes and macrophages, as these cells play a decisive role in establishing the pathogenesis or cure. These cells are involved in controlling the growth of Leishmania and in modulating the adaptive immune responses. The heterogeneity and extensive plasticity of monocytes allow these cells to adjust their functional phenotypes in response to the pathogen-directed immunological cues. In Leishmania-infected host, the rate of myelopoiesis is augmented by enhanced monocytic lineage commitment and proliferation of myeloid progenitor cells both in the BM and at the site of infection. These newly generated monocytes play as "safe haven" for the parasite and also as the antigen-presenting cells for T cells to cause deregulated cytokine production. This altered monocytopoiesis is characterized by tissue-specific immune responses, spatiotemporal dynamics of immunoregulation and functional heterogeneity. In the presence of Th1 cytokines, monocytes exhibit a pro-inflammatory phenotype that protects the host from Leishmania. By contrast, in an environment of Th2 cytokines, monocytes display anti-inflammatory phenotype with pro-parasitic functions. In this review, we summarize the involvement of cytokines in the regulation of monocytopoiesis and differentiation of macrophages during leishmanial infection. Understanding the role of cytokines in regulating interactions between Leishmania and the host monocytes is key to developing new therapeutic interventions against leishmaniases.

ATP-Binding and Hydrolysis in Inflammasome Activation

The prototypical model for NOD-like receptor (NLR) inflammasome assembly includes nucleotide-dependent activation of the NLR downstream of pathogen- or danger-associated molecular pattern (PAMP or DAMP) recognition, followed by nucleation of hetero-oligomeric platforms that lie upstream of inflammatory responses associated with innate immunity. As members of the STAND ATPases, the NLRs are generally thought to share a similar model of ATP-dependent activation and effect. However, recent observations have challenged this paradigm to reveal novel and complex biochemical processes to discern NLRs from other STAND proteins. In this review, we highlight past findings that identify the regulatory importance of conserved ATP-binding and hydrolysis motifs within the nucleotide-binding NACHT domain of NLRs and explore recent breakthroughs that generate connections between NLR protein structure and function. Indeed, newly deposited NLR structures for NLRC4 and NLRP3 have provided unique perspectives on the ATP-dependency of inflammasome activation. Novel molecular dynamic simulations of NLRP3 examined the active site of ADP- and ATP-bound models. The findings support distinctions in nucleotide-binding domain topology with occupancy of ATP or ADP that are in turn disseminated on to the global protein structure. Ultimately, studies continue to reveal how the ATP-binding and hydrolysis properties of NACHT domains in different NLRs integrate with signaling modules and binding partners to control innate immune responses at the molecular level.

Induction of Innate Immune Memory by Engineered Nanoparticles in Monocytes/Macrophages: From Hypothesis to Reality

The capacity of engineered nanoparticles to activate cells of the innate immune system, in particular monocytes and macrophages, is considered at the basis of their toxic/inflammatory effects. It is, however, evident that even nanoparticles that do not directly induce inflammatory activation, and are therefore considered as safe, can nevertheless induce epigenetic modifications and affect metabolic pathways in monocytes and macrophages. Since epigenetic and metabolic changes are the main mechanisms of innate memory, we had previously proposed that nanoparticles can induce/modulate innate memory, that is, have the ability of shaping the secondary response to inflammatory challenges. In light of new data, it is now possible to support the original hypothesis and show that different types of nanoparticles can both directly induce innate memory, priming macrophages for a more potent response to subsequent stimuli, and modulate bacteria-induced memory by attenuating the priming-induced enhancement. This evidence raises two important issues. First, in addition to overt toxic/inflammatory effects, we should consider evaluating the capacity to induce innate memory and the related epigenetic and metabolic changes in the immunosafety assessment of nanomaterials, since modulation of innate memory may be at the basis of long-term unwanted immunological effects. The other important consideration is that this capacity of nanomaterials could open a new avenue in immunomodulation and the possibility of using engineered nanomaterials for improving immune responses to vaccines and resistance to infections, and modulate anomalous immune/inflammatory reactions in chronic inflammatory diseases, autoimmunity, and a range of other immune-related pathologies.

The untwining of immunosenescence and aging

From a holistic point of view, aging results from the cumulative erosion of the various systems. Among these, the immune system is interconnected to the rest as immune cells are present in all organs and recirculate through bloodstream. Immunosenescence is the term used to define the remodelling of immune changes during aging. Because immune cells-and particularly lymphocytes-can further differentiate after their maturation in response to pathogen recognition, it is therefore unclear when senescence is induced in these cells. Additionally, it is also unclear which signals triggers senescence in immune cells (i) aging per se, (ii) specific response to pathogens, (iii) underlying conditions, or (iv) inflammaging. In this review, we will cover the current knowledge and concepts linked to immunosenescence and we focus this review on lymphocytes and T cells, which represent the typical model for replicative senescence. With the evidence presented, we propose to disentangle the senescence of immune cells from chronological aging.

Immunosenescence is both functional/adaptive and dysfunctional/maladaptive

Alterations in the immune system with aging are considered to underlie many age-related diseases. However, many elderly individuals remain healthy until even a very advanced age. There is also an increase in numbers of centenarians and their apparent fitness. We should therefore change our unilaterally detrimental consideration of age-related immune changes. Recent data taking into consideration the immunobiography concept may allow for meaningful distinctions among various aging trajectories. This implies that the aging immune system has a homeodynamic characteristic balanced between adaptive and maladaptive aspects. The survival and health of an individual depends from the equilibrium of this balance. In this article, we highlight which parts of the aging of the immune system may be considered adaptive in contrast to those that may be maladaptive.

Possible contribution of trained immunity in faulty hormonal imprinting and DOHaD: Review and hypothesis

The faulty hormonal imprinting theory (published in 1980) and the DOHaD (Developmental Origin of Health and Disease theory (published in 1986) are twin-concepts: both justify the manifestation after long time (in adults) diseases which had been provoked in differentiating cells (e.g. during gestation). This was demonstrated using animal experiments as well, as comparative statistical methods (in human cases). However, there is no explanation for the tools of memorization (even after decades) of the early adversity and the tools of execution (manifestation) in adult age. It seems likely that immune memory is involved to the memorization of early adversity, up to the manifestation of the result (non-communicable diseases). Nevertheless, the relatively short timespan of adaptive immune memory makes this system insuitable for this function, however the newly recognized trained memory of the innate immune system seems to be theoretically suitable for the storage of the records and handling the sequalae, which is the epigenetic reprogramming in the time of provocation, without changes in base sequences (mutation). The flawed (damaged) program is manifested later, in adult age. Evidences are incomplete, so further animal experiments and human observations are needed for justifying the theory.

Epithelial Ovarian Cancer and the Immune System: Biology, Interactions, Challenges and Potential Advances for Immunotherapy

Recent advances in the understanding of immune function and the interactions with tumour cells have led to the development of various cancer immunotherapies and strategies for specific cancer types. However, despite some stunning successes with some malignancies such as melanomas and lung cancer, most patients receive little or no benefit from immunotherapy, which has been attributed to the tumour microenvironment and immune evasion. Although the US Food and Drug Administration have approved immunotherapies for some cancers, to date, only the anti-angiogenic antibody bevacizumab is approved for the treatment of epithelial ovarian cancer. Immunotherapeutic strategies for ovarian cancer are still under development and being tested in numerous clinical trials. A detailed understanding of the interactions between cancer and the immune system is vital for optimisation of immunotherapies either alone or when combined with chemotherapy and other therapies. This article, in two main parts, provides an overview of: (1) components of the normal immune system and current knowledge regarding tumour immunology, biology and their interactions; (2) strategies, and targets, together with challenges and potential innovative approaches for cancer immunotherapy, with attention given to epithelial ovarian cancer.

Aldosterone induces trained immunity: the role of fatty acid synthesis

AIMS

Supranormal levels of aldosterone are associated with an increased cardiovascular risk in humans, and with accelerated atherosclerosis in animal models. Atherosclerosis is a low-grade inflammatory disorder, with monocyte-derived macrophages as major drivers of plaque formation. Monocytes can adopt a long-term pro-inflammatory phenotype after brief stimulation with microbial pathogens or endogenous atherogenic lipoproteins via a process termed trained immunity. In this study, we aimed to investigate whether aldosterone can induce trained immunity in primary human monocytes in vitro and explored the underlying mechanism.

METHODS AND RESULTS

We exposed human monocytes to aldosterone for 24 h, after which they were rested to differentiate into monocyte-derived macrophages for 5 days, and re-stimulated with toll-like receptor 2 and 4 ligands on day 6. We demonstrated that aldosterone augments pro-inflammatory cytokine production and reactive oxygen species production in monocyte-derived macrophages after re-stimulation, via the mineralocorticoid receptor. Fatty acid synthesis was identified as a crucial pathway necessary for this induction of trained immunity and pharmacological inhibition of this pathway blunted aldosterone-induced trained immunity. At the level of gene regulation, aldosterone promoted enrichment of the transcriptionally permissive H3K4me3 modification at promoters of genes central to the fatty acid synthesis pathway.

CONCLUSION

Aldosterone induces trained immunity in vitro, which is dependent on epigenetically mediated up-regulation of fatty acid synthesis. These data provide mechanistic insight into the contribution of aldosterone to inflammation, atherosclerosis, and cardiovascular disease.

Immunometabolic control of trained immunity

Innate immune cells can adopt long-term inflammatory phenotypes following brief encounters with exogenous (microbial) or endogenous stimuli. This phenomenon is named trained immunity and can improve host defense against (recurrent) infections. In contrast, trained immunity can also be maladaptive in the context of chronic inflammatory disorders, such as atherosclerosis. Key to future therapeutic exploitation of this mechanism is thorough knowledge of the mechanisms driving trained immunity, which can be used as pharmacological targets. These mechanisms include profound changes in intracellular metabolism, which are closely intertwined with epigenetic reprogramming at the level of histone modifications. Glycolysis, glutamine replenishment of the tricarboxylic acid cycle with accumulation of fumarate, and the mevalonate pathway have all been identified as critical pathways for trained immunity in monocytes and macrophages. In this review, we provide a state-of-the-art overview of how these metabolic pathways interact with epigenetic programs to develop trained immunity.

Differential induction of innate memory in porcine monocytes by -glucan or bacillus Calmette-Guerin

Innate immunomodulation via induction of innate memory is one mechanism to alter the host’s innate immune response to reduce or prevent disease. Microbial products modulate innate responses with immediate and lasting effects. Innate memory is characterized by enhanced (training) or depressed (tolerance) innate immune responses, including pro-inflammatory cytokine production, to secondary exposure following a priming event. To investigate the ability of β-glucans and bacillus Calmette-Guerin to induce innate training or tolerance in pig cells, porcine monocytes were cultured with priming agonist (β-glucans or bacillus Calmette-Guerin) then re-stimulated 5 d later with a heterologous microbial agonist to determine induction of innate memory. Priming with β-glucan from Saccharomyces cerevisiae depressed IL-1β and TNF-α cytokine responses to re-stimulation with LPS, indicative of a tolerized state. However, bacillus Calmette-Guerin priming induced a trained state in porcine monocytes, as LPS re-stimulation enhanced IL-1β and TNF-α gene expression and protein production. We present the first evidence of innate memory in pig monocytes, with bacillus Calmette-Guerin (training) or Saccharomyces cerevisiae β-glucan (tolerance). Induction of a trained or tolerized state in vitro is a first step to identify agonists to alter the innate immune system at the animal level with the intent of enhancing disease resistance.

An Army Marches on Its Stomach: Metabolic Intermediates as Antimicrobial Mediators in Mycobacterium tuberculosis Infection

The cells of the immune system are reliant on their metabolic state to launch effective responses to combat mycobacterial infections. The bioenergetic profile of the cell determines the molecular fuels and metabolites available to the host, as well as to the bacterial invader. How cells utilize the nutrients in their microenvironment—including glucose, lipids and amino acids—to sustain their functions and produce antimicrobial metabolites, and how mycobacteria exploit this to evade the immune system is of great interest. Changes in flux through metabolic pathways alters the intermediate metabolites present. These intermediates are beginning to be recognized as key modulators of immune signaling as well as direct antimicrobial effectors, and their impact on tuberculosis infection is becoming apparent. A better understanding of how metabolism impacts immunity to Mycobacterium tuberculosis and how it is regulated and thus can be manipulated will open the potential for novel therapeutic interventions and vaccination strategies.

Biomarkers in critical care nutrition

The goal of nutrition support is to provide the substrates required to match the bioenergetic needs of the patient and promote the net synthesis of macromolecules required for the preservation of lean mass, organ function, and immunity. Contemporary observational studies have exposed the pervasive undernutrition of critically ill patients and its association with adverse clinical outcomes. The intuitive hypothesis is that optimization of nutrition delivery should improve ICU clinical outcomes. It is therefore surprising that multiple large randomized controlled trials have failed to demonstrate the clinical benefit of restoring or maximizing nutrient intake. This may be in part due to the absence of biological markers that identify patients who are most likely to benefit from nutrition interventions and that monitor the effects of nutrition support. Here, we discuss the need for practical risk stratification tools in critical care nutrition, a proposed rationale for targeted biomarker development, and potential approaches that can be adopted for biomarker identification and validation in the field.

Challenging the challenge: A randomized controlled trial evaluating the inflammatory response and pain perception of healthy volunteers after single-dose LPS administration, as a potential model for inflammatory pain in early-phase drug development

BACKGROUND AND AIMS

Following an infection, cytokines not only regulate the acute immune response, but also contribute to symptoms such as inflammatory hyperalgesia. We aimed to characterize the acute inflammatory response induced by a human endotoxemia model, and its effect on pain perception using evoked pain tests in two different dose levels. We also attempted to determine whether combining a human endotoxemia challenge with measurement of pain thresholds in healthy subjects could serve as a model to study drug effects on inflammatory pain.

METHODS AND RESULTS

This was a placebo-controlled, randomized, cross-over study in 24 healthy males. Twelve subjects were administered a bolus of 1 ng/kg LPS intravenously, and twelve 2 ng/kg LPS. Before days of placebo/LPS administration, subjects completed a full study day without study drug administration, but with identical pain threshold testing. Blood sampling and evoked pain tests (electrical burst and -stair, heat, pressure, and cold pressor test) were performed pre-dose and at frequent intervals up to 10hr post-dose. Data were analysed with a repeated-measures ANCOVA. For both dose levels, LPS induced an evident acute inflammatory response, but did not significantly affect any of the pain modalities. In a post-hoc analysis, lowering of pain thresholds was observed in the first 3 h after dosing, corresponding with the peak of the acute inflammatory response around 1-3 h post-dose.

CONCLUSION

Mild acute systemic inflammation, as induced by 1 ng/kg and 2 ng/kg LPS intravenous administration, did not significantly change pain thresholds in this study. The endotoxemia model in combination with evoked pain tests is not suitable to study acute inflammatory hyperalgesia in healthy males.

Human lipopolysaccharide models provide mechanistic and therapeutic insights into systemic and pulmonary inflammation

Inflammation is a key feature in the pathogenesis of sepsis and acute respiratory distress syndrome (ARDS). Sepsis and ARDS continue to be associated with high mortality. A key contributory factor is the rudimentary understanding of the early events in pulmonary and systemic inflammation in humans, which are difficult to study in clinical practice, as they precede the patient's presentation to medical services. Lipopolysaccharide (LPS), a constituent of the outer membrane of Gram-negative bacteria, is a trigger of inflammation and the dysregulated host response in sepsis. Human LPS models deliver a small quantity of LPS to healthy volunteers, triggering an inflammatory response and providing a window to study early inflammation in humans. This allows biological/mechanistic insights to be made and new therapeutic strategies to be tested in a controlled, reproducible environment from a defined point in time. We review the use of human LPS models, focussing on the underlying mechanistic insights that have been gained by studying the response to intravenous and pulmonary LPS challenge. We discuss variables that may influence the response to LPS before considering factors that should be considered when designing future human LPS studies.

OxLDL-mediated immunologic memory in endothelial cells

Trained innate immunity describes the metabolic reprogramming and long-term proinflammatory activation of innate immune cells in response to different pathogen or damage associated molecular patterns, such as oxidized low-density lipoprotein (oxLDL). Here, we have investigated whether the regulatory networks of trained innate immunity also control endothelial cell activation following oxLDL treatment. Human aortic endothelial cells (HAECs) were primed with oxLDL for 24 h. After a resting time of 4 days, cells were restimulated with the TLR2-agonist PAM3cys4. OxLDL priming induced a proinflammatory memory with increased production of inflammatory cytokines such as IL-6, IL-8 and MCP-1 in response to PAM3cys4 restimulation. This memory formation was dependent on TLR2 activation. Furthermore, oxLDL priming of HAECs caused characteristic metabolic and epigenetic reprogramming, including activation of mTOR-HIF1α-signaling with increases in glucose consumption and lactate production, as well as epigenetic modifications in inflammatory gene promoters. Inhibition of mTOR-HIF1α-signaling or histone methyltransferases blocked the observed phenotype. Furthermore, primed HAECs showed epigenetic activation of ICAM-1 and increased ICAM-1 expression in a HIF1α-dependent manner. Accordingly, live cell imaging revealed increased monocyte adhesion and transmigration following oxLDL priming. In summary, we demonstrate that oxLDL-mediated endothelial cell activation represents an immunologic event, which triggers metabolic and epigenetic reprogramming. Molecular mechanisms regulating trained innate immunity in innate immune cells also regulate this sustained proinflammatory phenotype in HAECs with enhanced atheroprone cell functions. Further research is necessary to elucidate the detailed metabolic regulation and the functional relevance for atherosclerosis formation in vivo.

Trained immunity as a molecular mechanism for BCG immunotherapy in bladder cancer

Intravesical BCG instillation is the gold-standard adjuvant immunotherapy for patients with high-risk non-muscle-invasive bladder cancer. However, the precise mechanism of action by which BCG asserts its beneficial effects is still unclear. BCG has been shown to induce a non-specific enhancement of the biological function in cells of the innate immune system, creating a de facto heterologous immunological memory that has been termed trained immunity. Trained immunity or innate immune memory enables innate immune cells to mount a more robust response to secondary non-related stimuli after being initially primed (or trained) by a challenge such as BCG. BCG-induced trained immunity is characterized by the metabolic rewiring of monocyte intracellular metabolism and epigenetic modifications, which subsequently lead to functional reprogramming effects, such as an increased production of cytokines, on restimulation. Results from BCG vaccination studies in humans show that trained immunity might at least partly account for the heterologous beneficial effects of BCG vaccination. Additionally, immunity might have a role in the effect of BCG immunotherapy for bladder cancer. Based on these indications, we propose that trained immunity could be one of the important mechanisms mediating BCG immunotherapy and could provide a basis for further improvements towards a personalized approach to BCG therapy in non-muscle-invasive bladder cancer.

Trained Immunity Based-Vaccines as a Prophylactic Strategy in Common Variable Immunodeficiency. A Proof of Concept Study

Background. A major concern in the care of common variable immunodeficiency (CVID) patients is the persistence of subclinical or recurrent respiratory tract infections (RRTI) despite adequate trough IgG levels, which impacts the quality of life (QoL) and morbidity. Therefore, the development of new approaches to prevent and treat infection, especially RRTI, is necessary. Objectives. We conducted a clinical observational study from May, 2016 to December, 2017 in 20 CVID patients; ten of these patients had a history of RRTI and received the polybacterial preparation MV130, a trained immunity-based vaccine (TIbV) to assess its impact on their QoL and prognosis. Methods. Subjects with RRTI received MV130 for 3 months and were followed up to 12 months after initiation of the treatment. The primary endpoint was a reduction in RRTI at the end of the study. We analyzed the pharmacoeconomic impact on the RRTI group before and after immunotherapy by estimating the direct and indirect costs, and assessed CVID-QoL and cytokine profile. Specific antibody responses to the bacteria contained in MV130 were measured. Results. The RRTI-group treated with TIbV MV130 showed a significant decrease in infection rate (p = 0.006) throughout the 12 months after initiation of the treatment. A decrease in antibiotic use and unscheduled outpatient visits was observed (p = 0.005 and p = 0.002, respectively). Significant increases in anti-pneumococcus and anti-MV130 IgA antibodies (p = 0.039 both) were detected after 12 months of MV130. Regarding the CVID QoL questionnaire, an overall decrease in the score by more than 50% was observed (p < 0.05) which demonstrated that patients experienced an improvement in their QoL. The pharmacoeconomic analysis showed that the real annual direct costs decreased up to 4 times per patient with the prophylactic intervention (p = 0.005). Conclusion. The sublingual administration of the TIbV MV130 significantly reduced the rate of respiratory infections, antibiotic use and unscheduled visits, while increasing specific IgA responses in CVID patients. Additionally, the CVID population felt that their QoL was improved, and a decrease in expenses derived from health care was predicted.

Pro-inflammatory Actions of Heme and Other Hemoglobin-Derived DAMPs

Damage associated molecular patterns (DAMPs) are endogenous molecules originate from damaged cells and tissues with the ability to trigger and/or modify innate immune responses. Upon hemolysis hemoglobin (Hb) is released from red blood cells (RBCs) to the circulation and give a rise to the production of different Hb redox states and heme which can act as DAMPs. Heme is the best characterized Hb-derived DAMP that targets different immune and non-immune cells. Heme is a chemoattractant, activates the complement system, modulates host defense mechanisms through the activation of innate immune receptors and the heme oxygenase-1/ferritin system, and induces innate immune memory. The contribution of oxidized Hb forms is much less studied, but some evidence show that these species might play distinct roles in intravascular hemolysis-associated pathologies independently of heme release. This review aims to summarize our current knowledge about the formation and pro-inflammatory actions of heme and other Hb-derived DAMPs.

Immunometabolism orchestrates training of innate immunity in atherosclerosis

Atherosclerosis is characterized by a persistent, low-grade inflammation of the arterial wall. Monocytes and monocyte-derived macrophages play a pivotal role in the various stages of atherosclerosis. In the past few years, metabolic reprogramming has been identified as an important controller of myeloid cell activation status. In addition, metabolic and epigenetic reprogramming are key regulatory mechanisms of trained immunity, which denotes the non-specific innate immune memory that can develop after brief stimulation of monocytes with microbial or non-microbial stimuli. In this review, we build the case that metabolic reprogramming of monocytes and macrophages, and trained immunity in particular, contribute to the pathophysiology of atherosclerosis. We discuss the specific metabolic adaptations, including changes in glycolysis, oxidative phosphorylation, and cholesterol metabolism, that have been reported in atherogenic milieus in vitro and in vivo. In addition, we will focus on the role of these metabolic pathways in the development of trained immunity.

Innate Immunomodulation in Food Animals: Evidence for Trained Immunity?

Antimicrobial resistance (AMR) is a significant problem in health care, animal health, and food safety. To limit AMR, there is a need for alternatives to antibiotics to enhance disease resistance and support judicious antibiotic usage in animals and humans. Immunomodulation is a promising strategy to enhance disease resistance without antibiotics in food animals. One rapidly evolving field of immunomodulation is innate memory in which innate immune cells undergo epigenetic changes of chromatin remodeling and metabolic reprogramming upon a priming event that results in either enhanced or suppressed responsiveness to secondary stimuli (training or tolerance, respectively). Exposure to live agents such as bacille Calmette-Guerin (BCG) or microbe-derived products such as LPS or yeast cell wall ß-glucans can reprogram or "train" the innate immune system. Over the last decade, significant advancements increased our understanding of innate training in humans and rodent models, and strategies are being developed to specifically target or regulate innate memory. In veterinary species, the concept of enhancing the innate immune system is not new; however, there are few available studies which have purposefully investigated innate training as it has been defined in human literature. The development of targeted approaches to engage innate training in food animals, with the practical goal of enhancing the capacity to limit disease without the use of antibiotics, is an area which deserves attention. In this review, we provide an overview of innate immunomodulation and memory, and the mechanisms which regulate this long-term functional reprogramming in other animals (e.g., humans, rodents). We focus on studies describing innate training, or similar phenomenon (often referred to as heterologous or non-specific protection), in cattle, sheep, goats, swine, poultry, and fish species; and discuss the potential benefits and shortcomings of engaging innate training for enhancing disease resistance.

Pristine graphene induces innate immune training

Graphene-based materials are of increasing interest for their potential use in biomedical applications. However, there is a need to gain a deeper understanding of how graphene modulates biological responses before moving towards clinical application. Innate immune training is a recently described phenomenon whereby cells of the innate immune system are capable of being programmed to generate an increased non-specific response upon subsequent challenge. This has been well established in the case of certain microbes and microbial products. However, little is known about the capacity of particulate materials, such as pristine graphene (pGr), to promote innate immune training. Here we report for the first time that while stimulation with pGr alone does not directly induce cytokine secretion by bone-marrow derived macrophages (BMDMs), it programs them for enhanced secretion of proinflammatory cytokines (IL-6, TNF-α) and a concomitant decrease in production of the regulatory cytokine, IL-10 after Toll-like receptor (TLR) ligand stimulation. This capacity of pGr to program cells for enhanced inflammatory responses could be overcome if the nanomaterial is incorporated in a collagen matrix. Our findings thus demonstrate the potential of graphene to modulate innate immunity over long timescales and have implications for the design and biomedical use of pGr-based materials.

A Potential Role for Epigenetically Mediated Trained Immunity in Food Allergy

The prevalence of IgE-mediated food allergy is increasing at a rapid pace in many countries. The association of high food allergy rates with Westernized lifestyles suggests the role of gene-environment interactions, potentially underpinned by epigenetic variation, in mediating this process. Recent studies have implicated innate immune system dysfunction in the development and persistence of food allergy. These responses are characterized by increased circulating frequency of innate immune cells and heightened inflammatory responses to bacterial stimulation in food allergic patients. These signatures mirror those described in trained immunity, whereby innate immune cells retain a “memory” of earlier microbial encounters, thus influencing subsequent immune responses. Here, we propose that a robust multi-omics approach that integrates immunological, transcriptomic, and epigenomic datasets, combined with well-phenotyped and longitudinal food allergy cohorts, can inform the potential role of trained immunity in food allergy.

The Aging of γδ T Cells

In the coming decades, many developed countries in the world are expecting the "greying" of their populations. This phenomenon poses unprecedented challenges to healthcare systems. Aging is one of the most important risk factors for infections and a myriad of diseases such as cancer, cardiovascular and neurodegenerative diseases. A common denominator that is implicated in these diseases is the immune system. The immune system consists of the innate and adaptive arms that complement each other to provide the host with a holistic defense system. While the diverse interactions between multiple arms of the immune system are necessary for its function, this complexity is amplified in the aging immune system as each immune cell type is affected differently-resulting in a conundrum that is especially difficult to target. Furthermore, certain cell types, such as γδ T cells, do not fit categorically into the arms of innate or adaptive immunity. In this review, we will first introduce the human γδ T cell family and its ligands before discussing parallels in mice. By covering the ontogeny and homeostasis of γδ T cells during their lifespan, we will better capture their evolution and responses to age-related stressors. Finally, we will identify knowledge gaps within these topics that can advance our understanding of the relationship between γδ T cells and aging, as well as age-related diseases such as cancer.

Arterial Wall Inflammation and Increased Hematopoietic Activity in Patients With Primary Aldosteronism

CONTEXT

Primary aldosteronism (PA) confers an increased risk of cardiovascular disease (CVD), independent of blood pressure. Animal models have shown that aldosterone accelerates atherosclerosis through proinflammatory changes in innate immune cells; human data are scarce.

OBJECTIVE

The objective of this article is to explore whether patients with PA have increased arterial wall inflammation, systemic inflammation, and reprogramming of monocytes.

DESIGN

A cross-sectional cohort study compared vascular inflammation on 2'-deoxy-2'-(18F)fluoro-D-glucose; (18F-FDG) positron emission tomography-computed tomography, systemic inflammation, and monocyte phenotypes and transcriptome between PA patients and controls.

SETTING

This study took place at Radboudumc and Rijnstate Hospital, the Netherlands.

PATIENTS

Fifteen patients with PA and 15 age-, sex-, and blood pressure-matched controls with essential hypertension (EHT) participated.

MAIN OUTCOME MEASURES AND RESULTS

PA patients displayed a higher arterial 18F-FDG uptake in the descending and abdominal aorta (P < .01, P < .05) and carotid and iliac arteries (both P < .01). In addition, bone marrow uptake was higher in PA patients (P < .05). Although PA patients had a higher monocyte-to-lymphocyte ratio (P < .05), systemic inflammatory markers, cytokine production capacity, and transcriptome of circulating monocytes did not differ. Monocyte-derived macrophages from PA patients expressed more TNFA; monocyte-derived macrophages of healthy donors cultured in PA serum displayed increased interleukin-6 and tumor necrosis factor-α production.

CONCLUSIONS

Because increased arterial wall inflammation is associated with accelerated atherogenesis and unstable plaques, this might importantly contribute to the increased CVD risk in PA patients. We did not observe inflammatory reprogramming of circulating monocytes. However, subtle inflammatory changes are present in the peripheral blood cell composition and monocyte transcriptome of PA patients, and in their monocyte-derived macrophages. Most likely, arterial inflammation in PA requires interaction between various cell types.

Rewiring of glucose metabolism defines trained immunity induced by oxidized low-density lipoprotein

Abstract

Stimulation of monocytes with microbial and non-microbial products, including oxidized low-density lipoprotein (oxLDL), induces a protracted pro-inflammatory, atherogenic phenotype sustained by metabolic and epigenetic reprogramming via a process called trained immunity. We investigated the intracellular metabolic mechanisms driving oxLDL-induced trained immunity in human primary monocytes and observed concomitant upregulation of glycolytic activity and oxygen consumption. In two separate cohorts of healthy volunteers, we assessed the impact of genetic variation in glycolytic genes on the training capacity of monocytes and found that variants mapped to glycolytic enzymes PFKFB3 and PFKP influenced trained immunity by oxLDL. Subsequent functional validation with inhibitors of glycolytic metabolism revealed dose-dependent inhibition of trained immunity in vitro. Furthermore, in vivo administration of the glucose metabolism modulator metformin abrogated the ability for human monocytes to mount a trained response to oxLDL. These findings underscore the importance of cellular metabolism for oxLDL-induced trained immunity and highlight potential immunomodulatory strategies for clinical management of atherosclerosis.

Key messages

Brief stimulation of monocytes to oxLDL induces a prolonged inflammatory phenotype.

This is due to upregulation of glycolytic metabolism.

Genetic variation in glycolytic genes modulates oxLDL-induced trained immunity.

Pharmacological inhibition of glycolysis prevents trained immunity.

Electronic supplementary material

The online version of this article (10.1007/s00109-020-01915-w) contains supplementary material, which is available to authorized users.

Natural and trained innate immunity against Mycobacterium tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) infection, remains a major global health emergency. It is estimated that one third of global population are affected, predominantly with latent granuloma form of the disease. Mtb co-evolved with humans, for its obligatory intra-macrophage phagosome habitat and slow replication, balanced against unique mycobacterial innate immunity, which appears to be highly complex. TB is transmitted via cough aerosol Mtb inhalation. Bovine TB attenuated Bacillus Calmette Guerin (BCG) live vaccine has been in practice for protection of young children from severe disseminated Mtb infection, but not sufficiently for their lungs, as obtained by trials in TB endemic community. To augment BCG vaccine-driven innate and adaptive immunity for neonates and better protection against adult pulmonary TB, a number of BCG pre-vaccination based, subset vaccine candidates have been tested via animal preclinical, followed by safe clinical trials. BCG also enhances innate macrophage trained immunity and memory, through primordial intracellular Toll-like receptors (TLRs) 7 and 9, which recognise distinct mycobacterial molecular pattern signature. This signature is transmitted by TLR signalling via nuclear factor-κB, for activating innate immune transcription and expression of gene profiling in a mycobacterial signature-specific manner. These are epigenetically imprinted in reprogramming of distinct chromatin areas for innate immune memory, to be recalled following lung reinfection. Unique TB innate immunity and its trained memory are considered independent from adaptive immune B and T cells. On the other hand, adaptive immunity is crucial in Mtb containment in granulomatous latency, supported by innate immune cell infiltration. In nearly 5-10 % of susceptible people, latent TB may be activated due to immune evasion by Mtb from intracellular phagosome within macrophage, perpetrating TB. However, BCG and new recombinant BCG vaccines have the capacity, as indicated in pre- and clinical trials, to overcome such Mtb evasion. Various strategies include pro-inflammatory-bactericidal type 1 polarisation (M1) phenotype of the infected macrophage, involving thrombospondin-TLR pathway. Saprophytic M. smegmatis-based recombinant vaccines are also promising candidates against TB. BCG vaccination of neonates/infants in TB endemic countries also reduced their pneumonia caused by various microbes independent of TB immunity. Here, we discuss host immune response against Mtb, its immune evasion strategies, and the important role innate immunity plays in the development of protection against TB.

Catecholamines Induce Trained Immunity in Monocytes In Vitro and In Vivo

RATIONALE

Exposure to high catecholamine levels is associated with inflammatory changes of myeloid cells and atherosclerosis, but the underlying mechanisms are only partly understood.

OBJECTIVE

To investigate whether the proinflammatory effects of noradrenaline and adrenaline can, in part, be explained by the induction of an immunologic memory in innate immune cells, termed trained immunity.

METHODS AND RESULTS

In vitro, we exposed human primary monocytes to (nor)adrenaline for 24 hours, after which cells were rested and differentiated to macrophages over 5 days. After restimulation with lipopolysaccharide on day 6, (nor)adrenaline-exposed cells showed increased TNF-α (tumor necrosis factor-α) production. This coincided with an increase in glycolysis and oxidative phosphorylation measured with Seahorse technology on day 6 before restimulation. Inhibition of the β-adrenoreceptor-cAMP signaling pathway prevented the induction of training. In vivo, we studied the functional, transcriptional, and epigenetic impact of peak-wise exposure to high catecholamine levels on monocytes isolated from pheochromocytoma/paraganglioma (PHEO) patients. In PHEO patients (n=10), the peripheral blood cell composition showed a myeloid bias and an increase of the inflammatory CD14++CD16+ (cluster of differentiation) intermediate monocyte subset compared with controls with essential hypertension (n=14). Ex vivo production of proinflammatory cytokines was higher in PHEO patients. These inflammatory changes persisted for 4 weeks after surgical removal of PHEO. Transcriptome analysis of circulating monocytes at baseline showed various differentially expressed genes in inflammatory pathways in PHEO patients; epigenetic profiling of the promoters of these genes suggests enrichment of the transcriptionally permissive chromatin mark H3K4me3 (trimethylation of lysine 4 on histone H3), indicative of in vivo training.

CONCLUSIONS

Catecholamines induce long-lasting proinflammatory changes in monocytes in vitro and in vivo, indicating trained immunity. Our data contribute to the understanding of pathways driving inflammatory changes in conditions characterized by high catecholamine levels and propose that trained immunity underlies the increased cardiovascular event rate in PHEO patients.

LXR Activation Induces a Proinflammatory Trained Innate Immunity-Phenotype in Human Monocytes

Objectives

The concept of trained innate immunity describes a long-term proinflammatory memory in innate immune cells. Trained innate immunity is regulated through reprogramming of cellular metabolic pathways including cholesterol and fatty acid synthesis. Here, we have analyzed the role of Liver X Receptor (LXR), a key regulator of cholesterol and fatty acid homeostasis, in trained innate immunity.

Methods and Results

Human monocytes were isolated and incubated with different stimuli for 24 h, including LXR agonists, antagonists and Bacillus Calmette-Guerin (BCG) vaccine. After 5 days resting time, cells were restimulated with the TLR2-agonist Pam3cys. LXR activation did not only increase BCG trained immunity, but also induced a long-term inflammatory activation by itself. This inflammatory activation by LXR agonists was accompanied by characteristic features of trained innate immunity, such as activating histone marks on inflammatory gene promoters and metabolic reprogramming with increased lactate production and decreased oxygen consumption rate. Mechanistically, LXR priming increased cellular acetyl-CoA levels and was dependent on the activation of the mevalonate pathway and IL-1β signaling. In contrast to mevalonate pathway inhibition, blocking fatty acid synthesis further increased proinflammatory priming by LXR.

Conclusion

We demonstrate that LXR activation induces a proinflammatory trained immunity phenotype in human monocytes through epigenetic and metabolic reprogramming. Our data reveal important novel aspects of LXR signaling in innate immunity.

New Insights in Candida albicans Innate Immunity at the Mucosa: Toxins, Epithelium, Metabolism, and Beyond

The mucosal surfaces of the human body are challenged by millions of microbes on a daily basis. Co-evolution with these microbes has led to the development of plastic mechanisms in both host and microorganisms that regulate the balance between preserving beneficial microbes and clearing pathogens. Candida albicans is a fungal pathobiont present in most healthy individuals that, under certain circumstances, can become pathogenic and cause everything from mild mucosal infections to life-threatening systemic diseases. As an essential part of the innate immunity in mucosae, epithelial cells elaborate complex immune responses that discriminate between commensal and pathogenic microbes, including C. albicans. Recently, several significant advances have been made identifying new pieces in the puzzle of host-microbe interactions. This review will summarize these advances in the context of our current knowledge of anti-Candida mucosal immunity, and their impact on epithelial immune responses to this fungal pathogen.

The inter-talk between Mycobacterium tuberculosis and the epigenetic mechanisms

Epigenetics regulate gene function without any alteration in the DNA sequence. The epigenetics represent one of the most important regulators in different cellular processes and have initially been developed in microorganisms as a protective strategy. The evaluation of the epigenetic mechanisms is also important in achieving an efficient control strategy in tuberculosis (TB). TB is one of the most significant epidemiological concerns in human history. Despite several in vivo and in vitro studies that have evaluated different epigenetic modifications in TB, many aspects of the association between epigenetics and TB are not fully understood. The current paper is aimed at reviewing our knowledge on histone modifications and DNA methylation modifications, as well as miRNAs regulation in TB.

Epigenetic Regulation of Vascular Diseases

Epigenetic regulatory mechanisms, encompassing diverse molecular processes including DNA methylation, histone post-translational modifications, and noncoding RNAs, are essential to numerous processes such as cell differentiation, growth and development, environmental adaptation, aging, and disease states. In many cases, epigenetic changes occur in response to environmental cues and lifestyle factors, resulting in persistent changes in gene expression that affect vascular disease risk during the lifetime of the individual. Biological aging-a powerful cardiovascular risk factor-is partly genetically determined yet strongly influenced by traditional risk factors, reflecting epigenetic modulation. Quantification of specific DNA methylation patterns may serve as an accurate predictor of biological age-a concept known as the epigenetic clock, which could help to refine cardiovascular risk assessment. Epigenetic reprogramming of monocytes rewires cellular immune signaling and induces a metabolic shift toward aerobic glycolysis, thereby increasing innate immune responses. This form of trained epigenetic memory can be maladaptive, thus augmenting vascular inflammation. Somatic mutations in epigenetic regulatory enzymes lead to clonal hematopoiesis of indeterminate potential, a precursor of hematologic malignancies and a recently recognized cardiovascular risk factor; moreover, epigenetic regulators are increasingly being targeted in cancer therapeutics. Thus, understanding epigenetic regulatory mechanisms lies at the intersection between cancer and cardiovascular disease and is of paramount importance to the burgeoning field of cardio-oncology (Graphic Abstract).

Gold Nanoparticles Modulate BCG-Induced Innate Immune Memory in Human Monocytes by Shifting the Memory Response towards Tolerance

Innate immune memory is characterized by a modulation in the magnitude with which innate immune cells such as monocytes and macrophages respond to potential dangers, subsequent to previous exposure to the same or unrelated agents. In this study, we have examined the capacity of gold nanoparticles (AuNP), which are already in use for therapeutic and diagnostic purposes, to modulate the innate memory induced by bacterial agents. The induction of innate memory was achieved in vitro by exposing human primary monocytes to bacterial agents (lipopolysaccharide -LPS-, or live Bacille Calmette-Guérin -BCG) in the absence or presence of AuNP. After the primary activation, cells were allowed to return to a resting condition, and eventually re-challenged with LPS. The induction of memory was assessed by comparing the response to the LPS challenge of unprimed cells with that of cells primed with bacterial agents and AuNP. The response to LPS was measured as the production of inflammatory (TNFα, IL-6) and anti-inflammatory cytokines (IL-10, IL-1Ra). While ineffective in directly inducing innate memory per se, and unable to influence LPS-induced tolerance memory, AuNP significantly affected the memory response of BCG-primed cells, by inhibiting the secondary response in terms of both inflammatory and anti-inflammatory factor production. The reprogramming of BCG-induced memory towards a tolerance type of reactivity may open promising perspectives for the use of AuNP in immunomodulatory approaches to autoimmune and chronic inflammatory diseases.