Advances in understanding molecular regulation of innate immune memory

© 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).The epigenetic and functional reprogramming of immune genes during induction of trained immunity is accompanied by the metabolic rewiring of cellular state. This memory is induced in the hematopoietic niche and propagated to daughter cells, generating epigenetically and metabolically reprogrammed innate immune cells that are greatly enhanced in their capacity to resolve inflammation. In particular, these cells show accumulation of H3K4me3 and H3K27Ac epigenetic marks on multiple immune gene promoters and associated enhancers. However, the mechanism governing how these epigenetic marks accumulate at discrete immune gene loci has been poorly understood, until now. Here, we discuss some recent advances in the regulation of trained immunity, with a particular focus on the mechanistic role of a novel class of long non-coding RNAs in the establishment of epigenetic marks on trained immune gene promoters.M.G.N. was supported by a Spinoza Grant of the Netherlands Organization for Scientific Research. L.A.B.J. was supported by a Competitiveness Operational Program grant of the Romanian Ministry of European Funds (HINT, ID P_37_762; MySMIS 103587). M.M.M. research is supported by a Department of Science and Technology Centre of Competence Grant, an SA Medical Research Council SHIP grant, and a CSIR Parliamentary Grant, all to M.M.M, and M.M.M. is a Chan Zuckerberg Investigator of the Chan Zuckerberg Initiative.info:eu-repo/semantics/publishedVersio

IL-17 produced by Paneth cells drives TNF-induced shock

Tumor necrosis factor (TNF) has very potent antitumor activity, but it also provokes a systemic inflammatory response syndrome that leads to shock, organ failure, and death. Here, we demonstrate that interleukin (IL)-17, a proinflammatory cytokine known to be produced mainly by activated T cells, has a critical role in this process. Antiserum against IL-17 or deletion of Il17r protected mice against a lethal TNF challenge. Serum levels of TNF-induced IL-6 and nitric oxide metabolites were significantly reduced in mice deficient in the IL-17R. TNF-induced leukocyte influx in the small intestine was reduced, and there was no injury to the small intestine. Surprisingly, electron microscopy showed that IL-17 was constitutively present in Paneth cells of the crypts. Upon TNF challenge, the intracellular pool of IL-17 in these cells was drastically reduced, suggesting rapid release of IL-17 from the granules of Paneth cells. Our findings assign a novel role for IL-17 in an acute inflammation and identify Paneth cells as a source of the IL-17 that plays a role in this process. These data indicate that innate immune cytokine responses in the local mucosa may participate in rapidly amplifying responses to systemic inflammatory challenges

Potent induction of trained immunity by Saccharomyces cerevisiae β-glucans

Candida albicans cell wall component β-glucan has been extensively studied for its ability to induce epigenetic and functional reprogramming of innate immune cells, a process termed trained immunity. We show that a high-complexity blend of two individual β-glucans from Saccharomyces cerevisiae possesses strong bioactivity, resulting in an enhanced trained innate immune response by human primary monocytes. The training required the Dectin-1/CR3, TLR4, and MMR receptors, as well as the Raf-1, Syk, and PI3K downstream signaling molecules. By activating multiple receptors and downstream signaling pathways, the components of this β-glucan preparation are able to act synergistically, causing a robust secondary response upon an unrelated challenge. In in-vivo murine models of melanoma and bladder cell carcinoma, pre-treatment of mice with the β-glucan preparation led to a significant reduction in tumor growth. These insights may aid in the development of future therapies based on β-glucan structures that induce an effective trained immunity response

Trained Immunity or Tolerance: Opposing Functional Programs Induced in Human Monocytes After Engagement of Various Pattern Recognition Receptors

Upon priming with Candida albicans or with the fungal cell wall component β-glucan, monocytes respond with an increased cytokine production upon restimulation, a phenomenon termed trained immunity. In contrast, the prestimulation of monocytes with lipopolysaccharide has long been known to induce tolerance. Because the vast majority of commensal microorganisms belong to bacterial or viral phyla, we sought to systematically investigate the functional reprogramming of monocytes induced by the stimulation of pattern recognition receptors (PRRs) with various bacterial or viral ligands. Monocytes were functionally programmed for either enhanced (training) or decreased (tolerance) cytokine production, depending on the type and concentration of ligand they encountered. The functional reprogramming of monocytes was also associated with cell shape, granulocity, and cell surface marker modifications. The training effect required p38- and Jun N-terminal protein kinase (JNK)-mediated mitogen-activated protein kinase (MAPK) signaling, with specific signaling patterns directing the functional fate of the cell. The long-term effects on the function of monocytes were mediated by epigenetic events, with both histone methylation and acetylation inhibitors blocking the training effects. In conclusion, our experiments identify the ability of monocytes to acquire adaptive characteristics after prior activation with a wide variety of ligands. Trained immunity and tolerance are two distinct and opposing functional programs induced by the specific microbial ligands engaging the monocytes

Genetic regulators of cytokine responses upon BCG vaccination in children from West Africa

Genetic variation is a key factor influencing cytokine production capacity, but which genetic loci regulate cytokine production before and after vaccination, particularly in African population is unknown. Here, we aimed to identify single-nucleotide polymorphisms (SNPs) controlling cytokine responses (cQTLs) after microbial stimulation in infants of West-African ancestry, comprising of low-birth-weight neonates randomized to bacillus Calmette–Guérin (BCG) vaccine-at-birth (intervention) or to the usual delayed BCG (control). Genome-wide cytokine QTL mapping revealed 12 independent cQTLs loci, of which the LINC01082-LINC00917 locus influenced more than half of the cytokine-stimulation pairs assessed. Furthermore, nine distinct cQTLs were found among infants randomized to BCG. Functional validation confirmed that several complement genes affect cytokine response after BCG vaccination. We observed a limited overlap of common cQTLs between the West-African infants and cohorts of Western European individuals. These data reveal strong population-specific genetic effects on cytokine production and may indicate new opportunities for therapeutic intervention and vaccine development in African populations.</p

Chronic HIV infection induces transcriptional and functional reprogramming of innate immune cells

Chronic inflammation and immune dysfunction play a key role in the development of non-AIDS-related comorbidities. The aim of our study was to characterize the functional phenotype of immune cells in people living with HIV (PLHIV). We enrolled a cross-sectional cohort study of PLHIV on stable antiretroviral therapy and healthy controls. We assessed ex vivo cytokine production capacity and transcriptomics of monocytes and T cells upon bacterial, fungal, and viral stimulation. PLHIV exhibited an exacerbated proinflammatory profile in monocyte-derived cytokines, but not in lymphocyte-derived cytokines. Particularly, the production of the IL-1 beta to imiquimod, E. coli LPS, and Mycobacterium tuberculosis was increased, and this production correlated with plasma concentrations of high-sensitivity C-reactive protein and soluble CD14. This increase in monocyte responsiveness remained stable over time in subsequent blood sampling after more than 1 year. Transcriptome analyses confirmed priming of the monocyte IL-1 beta pathway, consistent with a monocyte-trained immunity phenotype. Increased plasma concentrations of beta-glucan, a well-known inducer of trained immunity, were associated with increased innate cytokine responses. Monocytes of PLHIV exhibited a sustained proinflammatory immune phenotype with priming of the IL-1 beta pathway. Training of the innate immune system in PLHIV likely plays a role in long-term HIV complications and provides a promising therapeutic target for inflammation-related comorbidities

A functional genomics approach reveals suggestive quantitative trait loci associated with combined TLR4 and BCP crystal-induced inflammation and osteoarthritis

Objective: Basic calcium phosphate (BCP) crystals can activate the NLRP3 inflammasome and are potentially involved in the pathogenesis of osteoarthritis (OA). In order to elucidate relevant inflammatory mechanisms in OA, we used a functional genomics approach to assess genetic variation influencing BCP crystal-induced cytokine production. Method: Peripheral blood mononuclear cells (PBMCs) were isolated from healthy volunteers who were previously genotyped and stimulated with BCP crystals and/or lipopolysaccharide (LPS) after which cytokines release was assessed. Cytokine quantitative trait locus (cQTL) mapping was performed. For in vitro validation of the cQTL located in anoctamin 3 (ANO3), PBMCs were incubated with Tamoxifen and Benzbromarone prior to stimulation. Additionally, we performed co-localisation analysis of our top cQTLs with the most recent OA meta-analysis of genome-wide association studies (GWAS). Results: We observed that BCP crystals and LPS synergistically induce IL-1β in human PBMCs. cQTL analysis revealed several suggestive loci influencing cytokine release upon stimulation, among which are quantitative trait locus annotated to ANO3 and GLIS3. As functional validation, anoctamin inhibitors reduced IL-1β release in PBMCs after stimulation. Co-localisation analysis showed that the GLIS3 locus was shared between LPS/BCP crystal-induced IL-1β and genetic association with Knee OA. Conclusions: We identified and functionally validated a new locus, ANO3, associated with LPS/BCP crystal-induced inflammation in PBMCs. Moreover, the cQTL in the GLIS3 locus co-localises with the previously found locus associated with Knee OA, suggesting that this Knee OA locus might be explained through an inflammatory mechanism. These results form a basis for further exploration of inflammatory mechanisms in OA.</p

Differential Effects of Environmental and Genetic Factors on T and B Cell Immune Traits

Effective immunity requires a complex network of cellular and humoral components that interact with each other and are influenced by different environmental and host factors. We used a systems biology approach to comprehensively assess the impact of environmental and genetic factors on immune cell populations in peripheral blood, including associations with immunoglobulin concentrations, from ∼500 healthy volunteers from the Human Functional Genomics Project. Genetic heritability estimation showed that variations in T cell numbers are more strongly driven by genetic factors, while B cell counts are more environmentally influenced. Quantitative trait loci (QTL) mapping identified eight independent genomic loci associated with leukocyte count variation, including four associations with T and B cell subtypes. The QTLs identified were enriched among genome-wide association study (GWAS) SNPs reported to increase susceptibility to immune-mediated diseases. Our systems approach provides insights into cellular and humoral immune trait variability in humans

Engineering cytokine therapeutics

Cytokines have pivotal roles in immunity, making them attractive as therapeutics for a variety of immune-related disorders. However, the widespread clinical use of cytokines has been limited by their short blood half-lives and severe side effects caused by low specificity and unfavourable biodistribution. Innovations in bioengineering have aided in advancing our knowledge of cytokine biology and yielded new technologies for cytokine engineering. In this Review, we discuss how the development of bioanalytical methods, such as sequencing and high-resolution imaging combined with genetic techniques, have facilitated a better understanding of cytokine biology. We then present an overview of therapeutics arising from cytokine re-engineering, targeting and delivery, mRNA therapeutics and cell therapy. We also highlight the application of these strategies to adjust the immunological imbalance in different immune-mediated disorders, including cancer, infection and autoimmune diseases. Finally, we look ahead to the hurdles that must be overcome before cytokine therapeutics can live up to their full potential