Comprehensive transcriptome characterization deciphers mechanisms underpinning the positive selection of B cells in germinal centers.
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ABSTRACT:
ORGANISM(S): Mus musculus Homo sapiens
PROVIDER: GSE278743 | GEO | 2024/10/04
REPOSITORIES: GEO
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Project description:Alternative splicing (AS) and translational regulation play major roles in the activation and differentiation of immune cells. Previous studies using short-read sequencing linked individual AS events in germinal center (GC) B cells to proliferation and survival. To establish a more comprehensive understanding of transcript isoform changes that accompany B cell selection in the GC we developed a workflow for long-read nanopore sequencing. MYC expression by GC B cells marks cells undergoing a programme of AS which includes the removal of poison exons (PE) in splicing factors SRSF3 and SRSF7. These are crucial for B cell expansion and regulate transcripts encoding the translation machinery which is markedly increased upon positive selection of the GC B cell.
2024-10-04 | GSE278742 | GEO
Project description:Comprehensive transcriptome characterization deciphers mechanisms underpinning the positive selection of B cells in germinal centers.
| PRJNA1168544 | ENA
Project description:Comprehensive transcriptome characterization deciphers mechanisms underpinning the positive selection of B cells in germinal centers. [mouse short-read]
| PRJNA1168549 | ENA
Project description:The population dynamics theory of B cells in a typical germinal center could play an important role in revealing how affinity maturation is achieved. However, the existing models encountered some conflicts with experiments. To resolve these conflicts, we present a coarse-grained model to calculate the B cell population development in affinity maturation, which allows a comprehensive analysis of its parameter space to look for optimal values of mutation rate, selection strength, and initial antibody-antigen binding level that maximize the affinity improvement. With these optimized parameters, the model is compatible with the experimental observations such as the approximately 100-fold affinity improvements, the number of mutations, the hypermutation rate, and the "all or none" phenomenon. Moreover, we study the reasons behind the optimal parameters. The optimal mutation rate, in agreement with the hypermutation rate in vivo, results from a tradeoff between accumulating enough beneficial mutations and avoiding too many deleterious or lethal mutations. The optimal selection strength evolves as a balance between the need for affinity improvement and the requirement to pass the population bottleneck. These findings point to the conclusion that germinal centers have been optimized by evolution to generate strong affinity antibodies effectively and rapidly. In addition, we study the enhancement of affinity improvement due to B cell migration between germinal centers. These results could enhance our understanding of the functions of germinal centers.
| S-EPMC2880589 | biostudies-literature
Project description:Antibody affinity maturation occurs in secondary lymphoid organs within germinal centers (GCs) where B cells mutate their antibody-encoding genes in the dark zone (DZ) followed by a selection of the high-affinity variants in the light zone (LZ) by T cells. The amount of the T cell-derived selection signals is proportional to the BCR affinity and the magnitude of Myc expression. However, since the lifetimes of Myc mRNA and protein are extremely short, it is unclear how high levels of Myc are maintained in the GC B cell to allow positive selection. Here, by measuring Myc transcripts in situ at the single-cell level, we find that T cell help promotes the frequency of Myc transcriptional bursts. T cell help primarily increases the number of Myc-positive cells rather than the amount of Myc per cell. Measurement of Myc intronic and exonic transcripts in situ demonstrates that positive selection is mediated by Myc transcriptional bursts through a rapid increase in the active transcription sites rather than an elevation in transcription rate or gene accessibility. Thus, the amount of Myc transcriptional bursts over time in the LZ, rather than Myc abundance, dictates B cell selection in germinal centers.
2024-10-15 | GSE237128 | GEO
Project description:Germinal center (GC) B cells evolve toward increased affinity by a Darwinian process that has been studied primarily in genetically restricted, hapten-specific responses. We explored the population dynamics of genetically diverse GC responses to two complex antigens-Bacillus anthracis protective antigen and influenza hemagglutinin-in which B cells competed both intra- and interclonally for distinct epitopes. Preferred VH rearrangements among antigen-binding, naive B cells were similarly abundant in early GCs but, unlike responses to haptens, clonal diversity increased in GC B cells as early "winners" were replaced by rarer, high-affinity clones. Despite affinity maturation, inter- and intraclonal avidities varied greatly, and half of GC B cells did not bind the immunogen but nonetheless exhibited biased VH use, V(D)J mutation, and clonal expansion comparable to antigen-binding cells. GC reactions to complex antigens permit a range of specificities and affinities, with potential advantages for broad protection.
| S-EPMC4794380 | biostudies-literature
Project description:Follicular regulatory T cells (Tfr) can play opposite roles in the regulation of germinal center (GC) responses. Depending on the studies, Tfr suppress or support GC and B cell affinity maturation. However, which factors determine positive vs. negative effects of Tfr on the GC B cell is unclear. In this study, we show that GC centrocytes that express MYC up-regulate expression of CCL3 chemokine that is needed for both the positive and negative regulation of GC B cells by Tfr. B cell-intrinsic expression of CCL3 contributes to Tfr-dependent positive selection of foreign Ag-specific GC B cells. At the same time, expression of CCL3 is critical for direct Tfr-mediated suppression of GC B cells that acquire cognate to Tfr nuclear proteins. Our study suggests that CCR5 and CCR1 receptors promote Tfr migration to CCL3 and highlights Ccr5 expression on the Tfr subset that expresses Il10. Based on our findings and previous studies, we suggest a model of chemotactically targeted checkpoint control of B cells undergoing positive selection in GCs by Tfr, where Tfr directly probe and license foreign antigen-specific B cells to complete their positive selection in GCs but, at the same time, suppress GC B cells that present self-antigens cognate to Tfr.
| S-EPMC10835130 | biostudies-literature
Project description:Epstein-Barr virus (EBV) infects germinal center (GC) B cells and establishes persistent infection in memory B cells. EBV-infected B cells can cause B-cell malignancies in humans with T- or natural killer-cell deficiency. We now find that EBV-encoded latent membrane protein 2A (LMP2A) mimics B-cell antigen receptor (BCR) signaling in murine GC B cells, causing altered humoral immune responses and autoimmune diseases. Investigation of the impact of LMP2A on B-cell differentiation in mice that conditionally express LMP2A in GC B cells or all B-lineage cells found LMP2A expression enhanced not only BCR signals but also plasma cell differentiation in vitro and in vivo. Conditional LMP2A expression in GC B cells resulted in preferential selection of low-affinity antibody-producing B cells despite apparently normal GC formation. GC B-cell-specific LMP2A expression led to systemic lupus erythematosus-like autoimmune phenotypes in an age-dependent manner. Epigenetic profiling of LMP2A B cells found increased H3K27ac and H3K4me1 signals at the zinc finger and bric-a-brac, tramtrack domain-containing protein 20 locus. We conclude that LMP2A reduces the stringency of GC B-cell selection and may contribute to persistent EBV infection and pathogenesis by providing GC B cells with excessive prosurvival effects.
| S-EPMC4577157 | biostudies-literature
Project description:Antibody affinity maturation occurs in germinal centers (GCs), where B cells cycle between the light zone (LZ) and the dark zone. In the LZ, GC B cells bearing immunoglobulins with the highest affinity for antigen receive positive selection signals from helper T cells, which promotes their rapid proliferation. Here we found that the RNA-binding protein PTBP1 was needed for the progression of GC B cells through late S phase of the cell cycle and for affinity maturation. PTBP1 was required for proper expression of the c-MYC-dependent gene program induced in GC B cells receiving T cell help and directly regulated the alternative splicing and abundance of transcripts that are increased during positive selection to promote proliferation.
| S-EPMC5842895 | biostudies-literature
Project description:Abstract: Epstein-Barr virus (EBV) infects germinal center (GC) B cells and establishes persistent infection in memory B cells. EBV-infected B cells sometimes cause B cell malignancies in humans with T- or NK-cell deficiency. We now find EBV-encoded Latent Membrane Protein 2A (LMP2A) to mimic B cell antigen receptor (BCR) signaling in murine GC B cells, causing altered humoral immune responses and autoimmune diseases. Investigation of the impact of LMP2A on B cell differentiation in mice that conditionally express LMP2A in GC B cells, or all B-lineage cells, found LMP2A expression enhanced not only BCR signals but also plasma-cell differentiation, in vitro and in vivo. Conditional LMP2A expression in GC B cells resulted in preferential selection of low-affinity antibody–producing B-cells despite apparently normal GC formation. GC B cell-specific LMP2A expression led to systemic lupus erythematosus-like autoimmune phenotypes in an age-dependent manner. Epigenetic profiling of LMP2A B cells found increased H3K27ac and H3K4me1 signals at the Zbtb20 locus. We conclude that LMP2A reduces the stringency of GC B cell selection and may contribute to persistent EBV infection and pathogenesis by providing GC B cells with pro-survival signals. Significance Statement: Epstein-Barr virus (EBV) is a human herpesvirus that establishes persistent infection of the B-cell compartment. EBV is associated with autoimmune diseases, including systemic lupus erythematosus (SLE). However, the molecular mechanisms by which EBV contributes to autoimmunity remain unclear. We used transgenic mouse models to study the role of EBV-encoded Latent membrane protein 2A (LMP2A), which mimics B-cell receptor signaling. Interestingly, LMP2A not only enhanced B-cell survival, but also upregulated the transcription factor Zbtb20 and promoted plasma cell differentiation. When expressed late in B-cell development, LMP2A also caused prominent features of SLE, including autoantibody production with kidney immune complex deposition. Our findings suggest that LMP2A has important roles in B cell activation, differentiation and the development of EBV-associated autoimmune diseases.
2015-10-01 | GSE71408 | GEO