Project description:The mechanisms involved in the maintenance of memory IgE responses are poorly understood, and the role played by germinal center (GC) IgE cells in these memory responses is particularly unclear. IgE B-cell differentiation is characterized by a transient GC phase, a bias towards the plasma cell (PC) fate, and dependence on sequential switching for the production of high-affinity IgE. We show here that IgE GC B cells are unfit to undergo the conventional GC differentiation program due to impaired B-cell receptor function and increased apoptosis. IgE GC cells fail to populate the GC light zone and are unable to contribute to the memory and long-lived PC compartments. Furthermore, we demonstrate that direct and sequential switching are linked to distinct B-cell differentiation fates: direct switching generates IgE GC cells, whereas sequential switching gives rise to IgE plasma cells. We propose a comprehensive model for the generation and memory of IgE responses. The purpose of this analysis was to: 1) identify expression differences between IgE and IgG1 B lymphocytes, 2) identify GC Dark Zone (DZ) and Light Zone (LZ) signatures of IgG1 GC cells. For that purpose, we compared in one experiment the gene expression patterns of IgE germinal center (GC) cells, IgG1 GC cells, IgE plasma cells (PC), IgG1 PC and naïve cells. In a second experiment, we compared the expression of IgG1 DZ GC cells with that of IgG1 LZ GC cells. Triplicates obtained from independent sorting experiments were used for all samples except two (IgG1 PC=2 samples; IgE PC=4 samples). Each sample was obtained from a pool of three individual mice. The mice used in the experiment were CeGFP BALB/c mice infected with the parasite N. brasiliensis. CeGFP mice carry an IRES-GFP KI cassette in the 3'UTR of membrane IgE. In these mice, GFP expression marks IgE cells, and a population of IgG1 cells with a rearrangement to Cepsilon in the non-productive (VDJ negative) IgH chromosome.
Project description:To obtain insight into the genetic basis of the increase of functional activity of memory B cells over time, we compared the gene expression profiles of day 7 and day 40 NP-specific/IgG1 memory B cells, GC B cells and plasma cells in immunized WT mice and naïve B cells, before and after activation in vitro. Total RNAs in three replicates of NP-specific/IgG1 memory B cells, GC B cells and plasma cells in immunized WT mice at day 7 and 40 postimmunization and naïve follicular and marginal zone B cells, before and after activation in vitro, were amplified and labeled according to the Affymetrix's instructions. cRNA was hybridized to Mouse Genome 430 2.0 GeneChips (Affymetrix).
Project description:Long-lived plasma cells (PCs) secrete antibodies that can provide sustained immunity against infection. It has been proposed that high affinity cells are preferentially selected into this compartment, potentiating the immune response. We used single cell RNA-seq to track the germinal center (GC) development of Ighg2A10 cells, specific for the Plasmodium falciparum circumsporozoite protein (PfCSP). Following immunization with Plasmodium sporozoites we identified 3 populations of cells in the GC light zone. One population expressed a gene signature associated with the initiation of PC differentiation and had an enhanced propensity to form PCs in vitro. Unexpectedly, the estimated affinity of this putative pre-PC population was indistinguishable from cells in the GC generally. This was also true when high- or low-avidity recombinant PfCSP proteins were used as immunogens. Immunization with low-avidity PfCSP did, however, induce increased affinity maturation. Collectively these findings suggest that the initiation of PC development in the GC occurs via an affinity independent process.
Project description:Long-lived plasma cells (PCs) secrete antibodies that can provide sustained immunity against infection. It has been proposed that high affinity cells are preferentially selected into this compartment, potentiating the immune response. We used single cell RNA-seq to track the germinal center (GC) development of Ighg2A10 cells, specific for the Plasmodium falciparum circumsporozoite protein (PfCSP). Following immunization with Plasmodium sporozoites we identified 3 populations of cells in the GC light zone. One population expressed a gene signature associated with the initiation of PC differentiation and had an enhanced propensity to form PCs in vitro. Unexpectedly, the estimated affinity of this putative pre-PC population was indistinguishable from cells in the GC generally. This was also true when high- or low-avidity recombinant PfCSP proteins were used as immunogens. Immunization with low-avidity PfCSP did, however, induce increased affinity maturation. Collectively these findings suggest that the initiation of PC development in the GC occurs via an affinity independent process.
Project description:Humoral immune responses require germinal centres (GC) for antibody affinity maturation. Within GC, B-cell proliferation and mutation are segregated from affinity-based positive selection in the dark zone (DZ) and light zone (LZ) substructures, respectively. While IL21 is known to be important in affinity maturation and GC maintenance, here we show it is required for both establishing normal zone representation and preventing the accumulation of cells in G1 cell cycle stage in the GC LZ.
Project description:High affinity B cell selection in the germinal center (GC) is governed by signals delivered by follicular helper T cells (Tfh) to B cells. Selected B cells undergo clonal expansion and affinity maturation in the GC dark zone in direct proportion to the amount of antigen they capture and present to Tfh cells in the light zone. Here we examined the mechanisms whereby Tfh cells program the number of GC B cell divisions. Gene expression analysis revealed that Tfh induce MYC expression in light zone B cells in direct proportion to antigen capture. Conditional Myc haplo-insufficiency or over-expression combined with cell division tracking showed that MYC expression produces a metabolic reservoir in selected light zone B cells that is proportional to the number of cell divisions in the dark zone. Thus, MYC constitutes the germinal center B cell division timer that when deregulated leads to emergence of B cell lymphoma.
Project description:The germinal center (GC) is a microanatomical compartment wherein high-affinity antibody-producing B cells are selectively expanded. B cells proliferate and mutate their antibody genes in the dark zone (DZ) of the GC and are then selected by T cells in the light zone (LZ) on the basis of affinity. Here, we show that T cell help regulates the speed of cell cycle phase transitions and DNA replication of GC B cells. Genome sequencing and single-molecule analyses revealed that T cell help shortens S phase by regulating replication fork progression while preserving the relative order of replication origin activation. Thus, high-affinity GC B cells are selected by a mechanism that involves prolonged dwell time in the DZ where selected cells undergo accelerated cell cycles.
Project description:The germinal center (GC) is a microanatomical compartment wherein high-affinity antibody-producing B cells are selectively expanded. B cells proliferate and mutate their antibody genes in the dark zone (DZ) of the GC and are then selected by T cells in the light zone (LZ) on the basis of affinity. Here, we show that T cell help regulates the speed of cell cycle phase transitions and DNA replication of GC B cells. Genome sequencing and single-molecule analyses revealed that T cell help shortens S phase by regulating replication fork progression while preserving the relative order of replication origin activation. Thus, high-affinity GC B cells are selected by a mechanism that involves prolonged dwell time in the DZ where selected cells undergo accelerated cell cycles. To determine whether GC B cells receiving high levels of T cell help show a specific change in gene expression, we compared DZ cells in the G1 phase of the cell cycle from αDEC-OVA and control αDEC-CS treated GCs using a fluorescent ubiquitination-based cell cycle indicator (Fucci-tg). RNA sequencing revealed that T cell-mediated selection produced an increase in gene expression programs associated with the cell cycle, metabolism, including the metabolism of nucleotides, and genes downstream of c-Myc and the E2F transcription factors.
Project description:Germinal centres (GC) are essential for the establishment of long-lasting antibody responses. In there, GC B cells rely on post-transcriptional RNA mechanisms for translating activation-associated transcriptional programs into functional changes in the cell proteome. However, we still lack knowledge about which are the critical proteins driving these key mechanisms. Here we show that the RNA binding proteins TIA1 and TIAL1 are required for the generation of long-lasting GC responses. TIA1 and TIAL1- deficient GC B cells fail to undergo antigen-mediated positive selection, expansion and differentiation into B cell clones producing high-affinity antibodies. Mechanistically, TIA1 and TIAL1 control the transcriptional identity of dark and light zone GC B cells and enable timely expression of the pro-survival molecule MCL1. Altogether, we demonstrate here that TIA1 and TIAL1 are key players in the post-transcriptional program that selects high-affinity antigen-specific GC B cells.