The development of high-affinity B cell memory is regulated through three separable phases, each involving antigen recognition by specific B cells and cognate T helper cells. Initially, antigen-primed B cells require cognate T cell help to gain entry into the germinal centre pathway to memory. Once in the germinal centre, B cells with variant B cell receptors must access antigens and present them to germinal centre T helper cells to enter long-lived memory B cell compartments. Following antigen recall, memory B cells require T cell help to proliferate and differentiate into plasma cells. A recent surge of information - resulting from dynamic B cell imaging in vivo and the elucidation of T follicular helper cell programmes - has reshaped the conceptual landscape surrounding the generation of memory B cells. In this Review, we integrate this new information about each phase of antigen-specific B cell development to describe the newly unravelled molecular dynamics of memory B cell programming.
"Two early key events are the up-regulation of the master transcription factor Bcl-6 and the chemokine receptor CXCR5, which results in migration to the border of the T and B cell zone in secondary lymphoid organs. Here, first contact with antigen-specific B cells occurs which seems to be critical for determination of the TFH phenotype and further migration deeper into the B cell follicle, where they provide B cell help by means of high expression of CD40L and production of the cytokines IL-4 and IL-21 (Crotty, 2011; McHeyzer-Williams et al., 2012). In contrast to other effector T cell subsets, TFH memory cells lose their prototypic markers when the GC reaction terminates (Weber et al., 2012). "
[Show abstract][Hide abstract] ABSTRACT: The co-stimulators ICOS (inducible T cell co-stimulator) and CD28 are both important for T follicular helper (TFH) cells, yet their individual contributions are unclear. Here, we show that each molecule plays an exclusive role at different stages of TFH cell development. While CD28 regulated early expression of the master transcription factor Bcl-6, ICOS co-stimulation was essential to maintain the phenotype by regulating the novel TFH transcription factor Klf2 via Foxo1. Klf2 directly binds to Cxcr5, Ccr7, Psgl-1, and S1pr1, and low levels of Klf2 were essential to maintain this typical TFH homing receptor pattern. Blocking ICOS resulted in relocation of fully developed TFH cells back to the T cell zone and reversion of their phenotype to non-TFH effector cells, which ultimately resulted in breakdown of the germinal center response. Our study describes for the first time the exclusive role of ICOS and its downstream signaling in the maintenance of TFH cells by controlling their anatomical localization in the B cell follicle.
Journal of Experimental Medicine 02/2015; 212(2). DOI:10.1084/jem.20141432 · 12.52 Impact Factor
"For example, IgG2a/c was shown to neutralize viruses and bacteria  , whereas IgE is able to mediate antibody-dependent cellular cytotoxicity (ADCC) against parasites . Taken together, pathogens specify initial B cell differentiation by directing cytokine production of antigen-specific T-helper cells  ; at later stages, Tfh cells provide cytokines and costimulatory factors to maintain and refine GC B cell responses  . "
[Show abstract][Hide abstract] ABSTRACT: Vaccines against acute infections execute their protective effects almost exclusively via the induction of antibodies. Development of protective vaccines against persisting pathogens lags behind probably because standard immunogens and application regimen do not sufficiently stimulate those circuits in B cell activation that mediate protection. In general, B cell responses against pathogen derived-antigens are generated through complex cellular interactions requiring the coordination of innate and adaptive immune mechanisms. In this review, we summarize recent findings from prototypic infection models to exemplify how generation of protective antibodies against persisting pathogens is imprinted by particular pathogen-derived factors and how distinct CD4(+) T cell populations determine the quality of these antibodies. Clearly, it is the high plasticity of these processes that is instrumental to drive tailored B cell responses that protect the host. In sum, application of novel knowledge on B cell plasticity and complexity can guide the development of rationally designed vaccines that elicit protective antibodies against persisting pathogens.
"Subsequently, the follicular pathway involves the formation of germinal centers (GCs), where B cells, interacting with T follicular helper (Tfh) and follicular dendritic cells, undergo somatic hypermutation and class switch recombination (CSR; Victora and Nussenzweig, 2012). Within the GC, cells expressing an antigen receptor of high affinity are positively selected, and will leave the GC either as memory cells, plasmablasts, or plasma cells (Oracki et al., 2010; McHeyzer-Williams et al., 2012). Some post-GC ASCs migrate to survival niches in the BM to become long-lived, nondividing plasma cells (Oracki et al., 2010). "
[Show abstract][Hide abstract] ABSTRACT: The transcriptional network regulating antibody-secreting cell (ASC) differentiation has been extensively studied, but our current understanding is limited. The mechanisms of action of known "master" regulators are still unclear, while the participation of new factors is being revealed. Here, we identify Zbtb20, a Bcl6 homologue, as a novel regulator of late B cell development. Within the B cell lineage, Zbtb20 is specifically expressed in B1 and germinal center B cells and peaks in long-lived bone marrow (BM) ASCs. Unlike Bcl6, an inhibitor of ASC differentiation, ectopic Zbtb20 expression in primary B cells facilitates terminal B cell differentiation to ASCs. In plasma cell lines, Zbtb20 induces cell survival and blocks cell cycle progression. Immunized Zbtb20-deficient mice exhibit curtailed humoral responses and accelerated loss of antigen-specific plasma cells, specifically from the BM pool. Strikingly, Zbtb20 induction does not require Blimp1 but depends directly on Irf4, acting at a newly identified Zbtb20 promoter in ASCs. These results identify Zbtb20 as an important player in late B cell differentiation and provide new insights into this complex process.
Journal of Experimental Medicine 04/2014; 211(5). DOI:10.1084/jem.20131831 · 12.52 Impact Factor
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