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      Epigenetics and Trained Immunity.

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          Abstract

          A growing body of clinical and experimental evidence has challenged the traditional understanding that only the adaptive immune system can mount immunological memory. Recent findings describe the adaptive characteristics of the innate immune system, underscored by its ability to remember antecedent foreign encounters and respond in a nonspecific sensitized manner to reinfection. This has been termed trained innate immunity. Although beneficial in the context of recurrent infections, this might actually contribute to chronic immune-mediated diseases, such as atherosclerosis. Recent Advances: In line with its proposed role in sustaining cellular memories, epigenetic reprogramming has emerged as a critical determinant of trained immunity. Recent technological and computational advances that improve unbiased acquisition of epigenomic profiles have significantly enhanced our appreciation for the complexities of chromatin architecture in the contexts of diverse immunological challenges.

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          Most cited references101

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          Epigenetic programming of monocyte-to-macrophage differentiation and trained innate immunity.

          Monocyte differentiation into macrophages represents a cornerstone process for host defense. Concomitantly, immunological imprinting of either tolerance or trained immunity determines the functional fate of macrophages and susceptibility to secondary infections. We characterized the transcriptomes and epigenomes in four primary cell types: monocytes and in vitro-differentiated naïve, tolerized, and trained macrophages. Inflammatory and metabolic pathways were modulated in macrophages, including decreased inflammasome activation, and we identified pathways functionally implicated in trained immunity. β-glucan training elicits an exclusive epigenetic signature, revealing a complex network of enhancers and promoters. Analysis of transcription factor motifs in deoxyribonuclease I hypersensitive sites at cell-type-specific epigenetic loci unveiled differentiation and treatment-specific repertoires. Altogether, we provide a resource to understand the epigenetic changes that underlie innate immunity in humans. Copyright © 2014, American Association for the Advancement of Science.
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            Candida albicans infection affords protection against reinfection via functional reprogramming of monocytes.

            Immunological memory in vertebrates is often exclusively attributed to T and B cell function. Recently it was proposed that the enhanced and sustained innate immune responses following initial infectious exposure may also afford protection against reinfection. Testing this concept of "trained immunity," we show that mice lacking functional T and B lymphocytes are protected against reinfection with Candida albicans in a monocyte-dependent manner. C. albicans and fungal cell wall β-glucans induced functional reprogramming of monocytes, leading to enhanced cytokine production in vivo and in vitro. The training required the β-glucan receptor dectin-1 and the noncanonical Raf-1 pathway. Monocyte training by β-glucans was associated with stable changes in histone trimethylation at H3K4, which suggests the involvement of epigenetic mechanisms in this phenomenon. The functional reprogramming of monocytes, reminiscent of similar NK cell properties, supports the concept of "trained immunity" and may be employed for the design of improved vaccination strategies. Copyright © 2012 Elsevier Inc. All rights reserved.
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              Histone exchange, chromatin structure and the regulation of transcription.

              The packaging of DNA into strings of nucleosomes is one of the features that allows eukaryotic cells to tightly regulate gene expression. The ordered disassembly of nucleosomes permits RNA polymerase II (Pol II) to access the DNA, whereas nucleosomal reassembly impedes access, thus preventing transcription and mRNA synthesis. Chromatin modifications, chromatin remodellers, histone chaperones and histone variants regulate nucleosomal dynamics during transcription. Disregulation of nucleosome dynamics results in aberrant transcription initiation, producing non-coding RNAs. Ongoing research is elucidating the molecular mechanisms that regulate chromatin structure during transcription by preventing histone exchange, thereby limiting non-coding RNA expression.
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                Author and article information

                Journal
                Antioxid. Redox Signal.
                Antioxidants & redox signaling
                Mary Ann Liebert Inc
                1557-7716
                1523-0864
                October 10 2018
                : 29
                : 11
                Affiliations
                [1 ] 1 Department of Internal Medicine, Radboud University Medical Center , Nijmegen, The Netherlands .
                [2 ] 2 Department for Genomics & Immunoregulation, Life and Medical Sciences Institute (LIMES), University of Bonn , Bonn, Germany .
                Article
                10.1089/ars.2017.7310
                6121175
                28978221
                15103b80-998d-48f1-8de5-2360f0824fe9
                History

                monocyte,macrophage,memory,trained immunity,epigenetics,innate immunity

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