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The Origin of the Plasma Cell Heterogeneity

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Book Series: Frontiers Research Topics ISSN: 16648714 ISBN: 9782889197347 Year: Pages: 80 DOI: 10.3389/978-2-88919-734-7 Language: English
Publisher: Frontiers Media SA
Subject: Allergy and Immunology --- Medicine (General)
Added to DOAB on : 2016-04-07 11:22:02
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Abstract

Plasma cells (PCs) are terminally differentiated B-cells producing large amounts of immunoglobulins (Ig). In humans, most of circulating Ig are produced by bone marrow plasma cells. PCs differentiate from activated naïve or memory B-cells usually activated by specific antigens. It is still controversial whether the regulation of PCs numbers and the “active” in vivo Ig diversity depend or not on non-specific reactivation of B-cells during infections. Depending on the stimulus (T-independent/T-dependent antigen, cytokines, partner cells) and B-cell types (naïve or memory, circulating or germinal center, lymph nodes or spleen, B1 or B2...), both the phenotype and isotype of PCs differ suggesting that PC diversity is either linked to B-cell diversity or to the type of stimulus or to both. Knowledge of the mechanisms supporting PC diversity has important consequences for the management of i) plasma cell neoplasia such as Multiple Myeloma and Waldenström's Macroglobulinemia, ii) vaccine protection against pathogens and iii) auto-immune diseases.

Keywords

Plasma cell --- B-cell --- differentiation --- Cell Cycle --- IL21 --- Autophagy --- B1 --- Autoimmunity --- Myeloma

Epigenetics of B Cells and Antibody Responses

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Book Series: Frontiers Research Topics ISSN: 16648714 ISBN: 9782889197903 Year: Pages: 121 DOI: 10.3389/978-2-88919-790-3 Language: English
Publisher: Frontiers Media SA
Subject: Allergy and Immunology --- Medicine (General)
Added to DOAB on : 2017-02-03 17:04:57
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Epigenetics is the study of changes in gene activity that are heritable but not caused by changes in the DNA sequence. By modulating gene activities, epigenetic changes regulate cell functions. They include DNA methylation, histone posttranslational modifications and gene silencing by the action of non-coding RNAs, particularly microRNAs. It is now clear that epigenetic changes regulate B cell development. By acting in concert with networks of transcription factors, they modulate the activation of B cell lineage specific gene programs and repress inappropriate gene transcription in particular B cell differentiation states. A hallmark of B cell development in the bone marrow is the assembly of the B cell receptor (BCR) for antigen through rearrangement of immunoglobulin heavy (IgH) and light (IgL) chain V(D)J genes, as mediated by RAG1/RAG2 recombinases. Ig V(D)J rearrangement critically times the progression from pro-B cell to pre-B cell and, finally, mature B cell. Such progression is modulated by epigenetic marks, such as DNA methylation and histone posttranslational modifications, that increase chromatin accessibility and target RAG/RAG2 to V, D and J DNA. It is also dependent on the expression of multiple microRNAs. Mice deficient in Ago2, which is essential for microRNA biogenesis and function, have B cell development blocked at the pro-B cell stage. In agreement with this, B cell specific ablation of microRNA by B cell-specific knockout of Dicer virtually blocks B cell differentiation at the pro-B to pre-B cell transition. After mature B cells encounter antigen, changes of the epigenetic landscape are induced by the same stimuli that drive the antibody response; such epigenetic changes underpin the maturation of the antibody response itself. They instruct those B cell differentiation processes, somatic hypermutation (SHM), class switch DNA recombination (CSR) and plasma cell differentiation, that are central to the maturation of the antibody response as well as differentiation of memory B cells. Inducible histone modifications, together with DNA methylation and microRNAs modulate the transcriptome, particularly the expression of activation-induced cytidine deaminase (AID), central to SHM and CSR, and B lymphocyte-induced maturation protein-1 (Blimp-1), which is central to plasma cell differentiation. Combinatorial histone modifications also function as histone codes in the targeting of the CSR and, possibly, the SHM machinery to the Ig locus by recruiting specific adaptors (histone code readers) that can in turn target and/or stabilize CSR/SHM factors. Epigenetic alterations in memory B cells contribute to their functionally distinction from their naive counterparts. Memory B cells inherit epigenetic information from their precursors and acquire new epigenetic marks, which make these resting B cells poised to promptly respond to antigen. The cross/feedback regulation of different epigenetic modifications/elements further increases the complexity of the B cell epigenome, which interacts with the genetic information for precise modulation of gene expression. It is increasingly evident that epigenetic dysregulation in B cells, including aberrant expression of microRNAs, can result in aberrant antibody responses to microbial pathogens, emergence of pathogenic autoantibodies or B cell neoplastic transformation. Epigenetic marks are potential targets for new therapeutics in autoimmunity and B cell malignancy.

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