BACKGROUNDInduction of innate immune memory, also termed trained immunity, by the antituberculosis vaccine bacillus Calmette-Guérin (BCG) contributes to protection against heterologous infections. ...However, the overall impact of BCG vaccination on the inflammatory status of an individual is not known; while induction of trained immunity may suggest increased inflammation, BCG vaccination has been epidemiologically associated with a reduced incidence of inflammatory and allergic diseases.METHODSWe investigated the impact of BCG (BCG-Bulgaria, InterVax) vaccination on systemic inflammation in a cohort of 303 healthy volunteers, as well as the effect of the inflammatory status on the response to vaccination. A targeted proteome platform was used to measure circulating inflammatory proteins before and after BCG vaccination, while ex vivo Mycobacterium tuberculosis- and Staphylococcus aureus-induced cytokine responses in peripheral blood mononuclear cells were used to assess trained immunity.RESULTSWhile BCG vaccination enhanced cytokine responses to restimulation, it reduced systemic inflammation. This effect was validated in 3 smaller cohorts, and was much stronger in men than in women. In addition, baseline circulating inflammatory markers were associated with ex vivo cytokine responses (trained immunity) after BCG vaccination.CONCLUSIONThe capacity of BCG to enhance microbial responsiveness while dampening systemic inflammation should be further explored for potential therapeutic applications.FUNDINGNetherlands Organization for Scientific Research, European Research Council, and the Danish National Research Foundation.
The tuberculosis vaccine bacillus Calmette-Guérin (BCG) has heterologous beneficial effects against non-related infections. The basis of these effects has been poorly explored in humans. In a ...randomized placebo-controlled human challenge study, we found that BCG vaccination induced genome-wide epigenetic reprograming of monocytes and protected against experimental infection with an attenuated yellow fever virus vaccine strain. Epigenetic reprogramming was accompanied by functional changes indicative of trained immunity. Reduction of viremia was highly correlated with the upregulation of IL-1β, a heterologous cytokine associated with the induction of trained immunity, but not with the specific IFNγ response. The importance of IL-1β for the induction of trained immunity was validated through genetic, epigenetic, and immunological studies. In conclusion, BCG induces epigenetic reprogramming in human monocytes in vivo, followed by functional reprogramming and protection against non-related viral infections, with a key role for IL-1β as a mediator of trained immunity responses.
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•BCG vaccination of humans induces genome-wide epigenetic reprogramming in monocytes•BCG-induced changes correlate with protection against experimental virus infection•Viremia reduction correlates with IL-1β upregulation, indicative of trained immunity•SNPs in IL1B affect the induction of trained immunity by BCG
In this paper, Arts et al. describe that BCG vaccination induces genome-wide epigenetic reprogramming of human monocytes that correlates with protection against experimental viral infection. Reduction of viremia correlated with upregulation of non-specific IL-1β production, and genetic polymorphisms in the IL-1 pathway affect the induction of trained immunity by BCG.
Summary
Immunological memory was long considered a trait exclusive to cells of the adaptive immune system. However, recent studies have shown that after activation of the innate immune system, innate ...immune cells may undergo long‐term functional reprogramming characterized by the ability to mount either a stronger or attenuated inflammatory response upon reactivation. This phenomenon, which has been termed trained immunity and is a de facto innate immune memory, is regulated by a network of integrated metabolic and epigenetic rewiring. The endogenous mediators that modulate trained immunity in the host are only partially understood, but increasing evidence supports the concept that the interleukin (IL)‐1 family of cytokines plays an important role. In this review, we will highlight key findings from studies that provide insight into the multifaceted roles of members of the IL‐1 family for trained immunity. Finally, we will discuss how the recent advances of our understanding on the role of IL‐1 cytokines in this field may lead to new therapeutic strategies for treatment of common conditions, such as IL‐1‐driven autoinflammatory diseases.
β-glucan is a potent inducer of epigenetic and functional reprogramming of innate immune cells, a process called “trained immunity,” resulting in an enhanced host response against secondary ...infections. We investigate whether β-glucan exposure confers protection against pulmonary Mycobacterium tuberculosis (Mtb) infection. β-glucan induces trained immunity via histone modifications at gene promoters in human monocytes, which is accompanied by the enhanced production of proinflammatory cytokines upon secondary Mtb challenge and inhibition of Mtb growth. Mice treated with β-glucan are significantly protected against pulmonary Mtb infection, which is associated with the expansion of hematopoietic stem and progenitor cells in the bone marrow and increased myelopoiesis. The protective signature of β-glucan is mediated via IL-1 signaling, as β-glucan shows no protection in mice lacking a functional IL-1 receptor (IL1R−/−). The administration of β-glucan may be used as a novel strategy in the treatment of mycobacterial infections and possibly as an adjuvant to improve anti-tuberculosis vaccines.
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•β-glucan induces protective trained immunity in human monocytes infected with Mtb•β-glucan induces protective trained immunity in mice infected with Mtb•β-glucan-mediated protection against Mtb is dependent on IL-1 signaling•β-glucan increases expansion of hematopoietic progenitors and myelopoiesis via IL-1
Moorlag et al. show that β-glucan induces protective trained immunity in human monocytes and in mice infected with virulent Mtb. β-glucan-mediated protection against Mtb is dependent on IL-1 signaling and is associated with the expansion of hematopoietic stem and progenitor cells in the bone marrow and increased myelopoiesis.
The bacillus Calmette-Guérin (BCG) vaccine protects against tuberculosis and heterologous infections but elicits high inter-individual variation in specific and nonspecific, or trained, immune ...responses. While the gut microbiome is increasingly recognized as an important modulator of vaccine responses and immunity in general, its potential role in BCG-induced protection is largely unknown.
Stool and blood were collected from 321 healthy adults before BCG vaccination, followed by blood sampling after 2 weeks and 3 months. Metagenomics based on de novo genome assembly reveals 43 immunomodulatory taxa. The nonspecific, trained immune response is detected by altered production of cytokines IL-6, IL-1β, and TNF-α upon ex vivo blood restimulation with Staphylococcus aureus and negatively correlates with abundance of Roseburia. The specific response, measured by IFN-γ production upon Mycobacterium tuberculosis stimulation, is associated positively with Ruminococcus and Eggerthella lenta. The identified immunomodulatory taxa also have the strongest effects on circulating metabolites, with Roseburia affecting phenylalanine metabolism. This is corroborated by abundances of relevant enzymes, suggesting alternate phenylalanine metabolism modules are activated in a Roseburia species-dependent manner.
Variability in cytokine production after BCG vaccination is associated with the abundance of microbial genomes, which in turn affect or produce metabolites in circulation. Roseburia is found to alter both trained immune responses and phenylalanine metabolism, revealing microbes and microbial products that may alter BCG-induced immunity. Together, our findings contribute to the understanding of specific and trained immune responses after BCG vaccination.
The antituberculosis vaccine Bacillus Calmette–Guérin (BCG) induces nonspecific protection against heterologous infections, at least partly through induction of innate immune memory (trained ...immunity). The amplitude of the response to BCG is variable, but the factors that influence this response are poorly understood. Metabolites, either released by cells or absorbed from the gut, are known to influence immune responses, but whether they impact BCG responses is not known. We vaccinated 325 healthy individuals with BCG, and collected blood before, 2 weeks and 3 months after vaccination, to assess the influence of circulating metabolites on the immune responses induced by BCG. Circulating metabolite concentrations after BCG vaccination were found to have a more pronounced impact on trained immunity responses, such as the increase in IL-1β and TNF-α production upon
Staphylococcus aureus
stimulation, than on specific adaptive immune memory, assessed as IFN-γ production in response to
Mycobacterium tuberculosis
. Circulating metabolites at baseline were able to predict trained immunity responses at 3 months after vaccination and enrichment analysis based on the metabolites positively associated with trained immunity revealed enrichment of the tricarboxylic acid (TCA) cycle and glutamine metabolism, both of which were previously found to be important for trained immunity. Several new metabolic pathways that influence trained immunity were identified, among which taurine metabolism associated with BCG-induced trained immunity, a finding validated in functional experiments. In conclusion, circulating metabolites are important factors influencing BCG-induced trained immunity in humans. Modulation of metabolic pathways may be a novel strategy to improve vaccine and trained immunity responses.
Long-term epigenetic reprogramming of innate immune cells in response to microbes, also termed “trained immunity,” causes prolonged altered cellular functionality to protect from secondary ...infections. Here, we investigated whether sterile triggers of inflammation induce trained immunity and thereby influence innate immune responses. Western diet (WD) feeding of Ldlr−/− mice induced systemic inflammation, which was undetectable in serum soon after mice were shifted back to a chow diet (CD). In contrast, myeloid cell responses toward innate stimuli remained broadly augmented. WD-induced transcriptomic and epigenomic reprogramming of myeloid progenitor cells led to increased proliferation and enhanced innate immune responses. Quantitative trait locus (QTL) analysis in human monocytes trained with oxidized low-density lipoprotein (oxLDL) and stimulated with lipopolysaccharide (LPS) suggested inflammasome-mediated trained immunity. Consistently, Nlrp3−/−/Ldlr−/− mice lacked WD-induced systemic inflammation, myeloid progenitor proliferation, and reprogramming. Hence, NLRP3 mediates trained immunity following WD and could thereby mediate the potentially deleterious effects of trained immunity in inflammatory diseases.
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•Western diet triggers innate immunity, NOD-like, and IFN signaling pathways•Western diet alters in vivo LPS responses of GMPs•Western diet induces long-lasting trained immunity in myeloid cells•NLRP3 recognizes Western diet and mediates trained immunity
Systemic inflammation induced by a Western diet is largely blunted by dietary changes, but myeloid cell-induced innate immune responses remain augmented and could potentially contribute to inflammatory disease.
Sepsis involves simultaneous hyperactivation of the immune system and immune paralysis, leading to both organ dysfunction and increased susceptibility to secondary infections. Acute activation ...of myeloid cells induced itaconate synthesis, which subsequently mediated innate immune tolerance in human monocytes. In contrast, induction of trained immunity by β-glucan counteracted tolerance induced in a model of human endotoxemia by inhibiting the expression of immune-responsive gene 1 (IRG1), the enzyme that controls itaconate synthesis. β-Glucan also increased the expression of succinate dehydrogenase (SDH), contributing to the integrity of the TCA cycle and leading to an enhanced innate immune response after secondary stimulation. The role of itaconate was further validated by IRG1 and SDH polymorphisms that modulate induction of tolerance and trained immunity in human monocytes. These data demonstrate the importance of the IRG1-itaconate-SDH axis in the development of immune tolerance and training and highlight the potential of β-glucan-induced trained immunity to revert immunoparalysis.
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•Itaconate is a central component of the inhibitory effects during immune tolerance•β-Glucan counteracts the tolerizing effects of LPS by inhibiting IRG1 expression•β-Glucan restores the expression of SDH in tolerant monocytes•β-Glucan-induced trained immunity has the potential to revert immunoparalysis
Domínguez-Andrés et al. demonstrate the importance of the IRG1-itaconate-SDH axis in the development of immune tolerance and training and highlight the potential of β-glucan-induced trained immunity to revert immunoparalysis, which can occur concurrently with immune hyperactivation in sepsis.
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.
Innate immune cells are able to build memory characteristics via a process termed “trained immunity.” Host factors that influence the magnitude of the individual trained immunity response remain ...largely unknown. Using an integrative genomics approach, our study aimed to prioritize and understand the role of specific genes in trained immunity responses. In vitro‐induced trained immunity responses were assessed in two independent population‐based cohorts of healthy individuals, the 300 Bacillus Calmette‐Guérin (300BCG; n = 267) and 200 Functional Genomics (200FG; n = 110) cohorts from the Human Functional Genomics Project. Genetic loci that influence cytokine responses upon trained immunity were identified by conducting a meta‐analysis of QTLs identified in the 300BCG and 200FG cohorts. From the identified QTL loci, we functionally validated the role of PI3K‐Akt signaling pathway and two genes that belong to the family of Siglec receptors (Siglec‐5 and Siglec‐14). Furthermore, we identified the H3K9 histone demethylases of the KDM4 family as major regulators of trained immunity responses. These data pinpoint an important role of metabolic and epigenetic processes in the regulation of trained immunity responses, and these findings may open new avenues for vaccine design and therapeutic interventions.
Using an immunogenomics approach, we identify genetic factors explaining interindividual variation in in vitro‐induced trained immunity responses. We highlight novel factors controlling trained immunity, including the KDM4 family of histone demethylases. These findings shed light on mechanisms underlying trained immunity and offer novel avenues for the design of therapeutics.
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