Previous studies using both high- and low-throughput sequencing techniques have already reported important differences between B cell subpopulations affecting their IgH repertoire composition, VDJ gene usage, mutations and clonality ( Berkowska et al., 2011 Mroczek et al., 2014 Galson et al., 2015 Wu et al., 2010). They include naïve, marginal zone (MZ), switched memory B cells and plasma cells (PC), which are mainly characterised by their differential expression of surface markers and by playing distinct roles in the adaptive immune response ( Leandro, 2013 ) High-throughput sequencing of the IgH repertoire (AIRR-seq) has made it possible to improve our understanding of the different components of the adaptive immune system in health and disease, and following vaccine challenge ( Mandric et al., 2020 Ghraichy et al., 2018 Galson et al., 2014 Lindau and Robins, 2017 Georgiou et al., 2014). Through developmental mechanisms and further differentiation in the periphery, several phenotypically distinct circulating B cell subpopulations are generated ( Allman and Pillai, 2008). Both direct switching and sequential switching upon a second round of antigen exposure have been reported ( Horns et al., 2016 Cameron et al., 2003 Zhang et al., 1994). Class switching is an essential mechanism during humoral immune responses as the constant region of an antibody determines its effector function ( Vidarsson et al., 2014). This process involves the replacement of the proximal heavy chain constant gene by a more distal gene. Subsequently, B cells with a mutated BCR providing increased antigen affinity are selected and show increased survival and proliferation capacity ( Zheng et al., 2005).įurthermore, class switch recombination (CSR) modifies the IgH constant region, resulting in the generation of B cells with nine different immunoglobulin isotypes or isotype subclasses, namely IgD, IgM, IgG1-4, IgA1/2 and IgE ( Stavnezer et al., 2008). Further development of B cells occurs in the periphery in response to stimulation with the process of somatic hypermutation (SHM) through which point mutations are introduced in the genes coding for the V(D)J part of the immunoglobulin heavy (IgH) and light chain ( Jolly et al., 1996). The generation of the heavy and light chain of the BCR is mediated by the random and imprecise process of V(D)J recombination ( Tonegawa, 1983). Introductionī cell development starts in the bone marrow where immature B cells must assemble and express on their surface a functional but non-self-reactive B cell antigen receptor (BCR) ( Lefranc and Lefranc, 2001). Overall, this study provides unprecedented insight over mechanisms of B cell repertoire control in peripherally circulating B cell subpopulations. Furthermore, certain IgH repertoire characteristics correlated with the position of the constant region on the IgH locus. Sorted subpopulations shared similar repertoire characteristics with their corresponding in silico separated subsets. Using advanced bioinformatic analysis and machine learning, we show that sorted B cell subpopulations are characterised by distinct repertoire characteristics on both the individual sequence and the repertoire level. Here, we sequenced the IgH repertoire of naïve, marginal zone, switched and plasma cells from 10 healthy adults along with matched unsorted and in silico separated CD19 + bulk B cells. These cells undergo developmental and maturational changes involving VDJ recombination, somatic hypermutation and class switch recombination, altogether shaping their immunoglobulin heavy chain (IgH) repertoire. Several human B cell subpopulations are recognised in the peripheral blood, which play distinct roles in the humoral immune response.
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