IL-6 contributes to an immune tolerance checkpoint in post germinal center B cells

The generation of a B cell repertoire involves producing and subsequently purging autoreactive B cells. Receptor editing, clonal deletion and anergy are key mechanisms of central B cell tolerance. Somatic mutation of antigen-activated B cells within the germinal center produces a second wave of autoreactivity; but the regulatory mechanisms that operate at this phase of B cell activation are poorly understood. We recently identified a post germinal center tolerance checkpoint, where receptor editing is re-induced to extinguish autoreactivity that is generated by somatic hypermutation. Re-induction of the recombinase genes RAG1 and RAG2 in antigen-activated B cells requires antigen to engage the B cell receptor and IL-7 to signal through the IL-7 receptor. We demonstrate that this process requires IL-6 to upregulate IL-7 receptor expression on post germinal center B cells. Diminishing IL-6 by blocking antibody or haplo-insufficiency leads to reduced expression of the IL-7 receptor and RAG and increased titers of anti-DNA antibodies following immunization with a peptide mimetope of DNA. The dependence on IL-6 to initiate receptor editing is B cell intrinsic. Interestingly, estradiol decreases IL-6 expression thereby increasing the anti-DNA response. Our data reveal a novel regulatory cascade to control post germinal center B cell autoreactivity.     

Bcl6 protein expression shapes pre-germinal center B cell dynamics and follicular helper T cell heterogeneity

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Highlights? Antigen-engaged B cells upregulate Bcl6 in the outer follicle to enter GC clusters ? Bcl6 in pre-GC B cells is important for sustaining conjugation with helper T cells ? Bcl6 protein is downmodulated in a number of Tfh cells after their development ? Bcl6-low Tfh cells rapidly terminate proliferation and upregulate IL-7 receptor     

Lymphotoxin α1β2 expression on B cells is required for follicular dendritic cell activation during the germinal center response

CD19‐deficient mice were used as a model to study follicular dendritic cell (FDC) activation because these mice have normal numbers of FDC‐containing primary follicles, but lack the ability to activate FDCs or form GCs. It was hypothesized that CD19 expression is necessary for B‐cell activation and upregulation of membrane lymphotoxin (mLT) expression, which promotes FDC activation. Using VCAM‐1 and FcγRII/III as FDC activation markers, it was determined that the adoptive transfer of CD19⁺ wild‐type B cells into CD19‐deficient hosts rescued GC formation and FDC activation, demonstrating that CD19 expression on B cells is required for FDC activation. In contrast, CD19⁺ donor B cells lacking mLT were unable to induce VCAM‐1 expression on FDCs, furthermore FcγRII/III upregulation was impaired in FDCs stimulated with mLT‐deficient B cells. VCAM‐1 expression on FDCs, but not FcγRII/III, was rescued when CD19‐deficient B cells expressing transgenic mLT were cotransferred into recipient mice with CD19⁺, mLT‐deficient B cells, suggesting that FDC activation requires the CD19‐dependent upregulation of mLT on activated B cells. Collectively, these data demonstrate that activated B cells are responsible for the initiation of FDC activation resulting in a microenvironment supportive of GC development and maintenance.     

High expression of methionine aminopeptidase type 2 in germinal center B cells and their neoplastic counterparts

Methionine aminopeptidase type 2 (MetAP2) is a bifunctional protein that plays critical roles in the regulation of protein synthesis and post-translational processing by (a) protecting the alpha subunit of eukaryotic initiation factor 2 from inhibitory phosphorylation by eukaryotic initiation factor 2 kinases and (b) removing the amino-terminal methionine residue from nascent protein. MetAP2 is also known as the molecular target of the angiogenesis inhibitor TNP-470. In addition, it has been recently suggested that MetAP2 has an antiapoptotic function in mesothelioma. To know the pattern of expression of MetAP2 in normal and neoplastic tissues, we raised two specific rabbit polyclonal Abs and examined the pattern of MetAP2 expression in various normal and pathologic specimens. Unexpectedly, we found a very high and selective expression of MetAP2 in germinal center B cells. In the germinal center, dark zone B cells tended to express more MetAP2 than light zone B cells. When 200 malignant lymphomas of various subtypes were studied, a high level of MetAP2 expression, equivalent to that observed in germinal center B cells, was noted exclusively on B-cell lymphoma subtypes that are currently regarded as the neoplastic counterparts of germinal center B cells. The expression of MetAP2 in diffuse large B-cell lymphomas correlated well with that of BCL6 (p < 0.05) but not with that of either CD10 or BCL2. These data suggest that MetAP2 has specific function(s) in germinal center B cells and that the function is shared by neoplastic counterparts of germinal center B cells.     

Role of follicular dendritic cells in the apoptosis of germinal center B cells

Follicular dendritic cells (FDCs) provide the most obvious source of antigens, which are essential for the differentiation of GC B cells. It has been reported that most proliferating B cells in germinal centers undergo apoptosis. Quantitative histology shows macrophages with apoptotic debris throughout the germinal center, the highest frequency of these cells being found in the dense FDC network. Based on these findings, we hypothesized that FDC may be involved in an apoptotic pathway of the germinal center B cells. To prove this hypothesis, we performed double immunohistochemical analysis using anti-FDC mAb and peanut agglutinin (PNA), with their respective TUNEL kits. Collated data showed that a great proportion of the apoptotic cells, most of which were positive for PNA, were in close contact with FDC, which indicated an interaction between FDC and B cells in the apoptotic pathway. Further studies using double immunohistochemical staining and FACS analyses demonstrated the expression of Fas-ligand (FasL) in a subset of the FDC. These results suggest that FDC may play a role in the apoptosis of germinal center B cells via Fas-FasL interaction.     

IL-2和IL-4联合诱导B细胞死亡受体CCR3的表达及其功能研究

目的　研究在IL 2和IL 4作用下 ,趋化性细胞因子受体CCR3在人生发中心 (germinalcenter,GC)B细胞上的表达及其功能特性。方法　采用流式细胞术检测人GCB细胞上CCR3表达和在CCR3配体eotaxin作用下B细胞的凋亡 ,实时定量RT PCR和Northernblot法检测GCB细胞内CCR3mRNA的表达 ,淋巴细胞趋化和黏附试验检测B细胞的趋化和黏附能力。结果　人GCB细胞极低表达趋化性细胞因子受体CCR3,经IL 2和IL 4作用后 ,GCB细胞高表达CCR3,但此时CCR3不能在其配体作用下诱导GCB细胞的趋化和黏附功能 ,而是诱导GCB细胞凋亡。结论　IL 2和IL 4联合诱导人GCB细胞CCR3表达 ,CCR3可能具有死亡受体的功能。     

Expression of Fas in B cells of the mouse germinal center and Fas-dependent killing of activated B cells

Fas is a cell-surface protein of 45 kDa. Binding of the Fasllgand (FasL) to Fas induces apoptosis in Fas-bearing cells.Analysis of mouse mutants in either Fas or FasL have indicatedthat the Fas system is involved in apoptosis of lymphocytes.To identify the cells expressing Fas, mouse spleen sectionswere analyzed by in situ hybridization and immunohistochemlstry.Fas mRNA was detected in the T cells of the inner region ofthe periarterial lymphatic sheath and the inner lumen of themarginal zone. The cells in the outer region of the periarteriallymphatic sheath weakly expressed Fas mRNA, whereas it was abundantin the B cells of germinal centers. Immunizing mice with keyholelimpet hemocyanin induced formation of many germinal centersin the spleen.The B cells in the activated germinal center expressedabundant Fas and underwent apoptosis.The in vitro activationof splenocytes with llpopolysaccharide induced Fas expressionin B cells and the B cells became sensitive to the Fas-mediatedapoptosis. These results suggest that Fas is involved in theactivation-induced death of B cells. Received 2 August 1995, accepted 1 September 1995.     

Human anti-smallpox long-lived memory B cells are defined by dynamic interactions in the splenic niche and long-lasting germinal center imprinting

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Cyclic re-entry of germinal center B cells and the efficiency of affinity maturation

Affinity maturation of the humoral immune response by somatic hypermutation is marked by a rapid and dramatic increase in affinity for the eliciting antigen. We suggest that the optimal mutation schedule is one in which periods of rapid mutation alternate with periods of mutation-free growth. The multicompartmental structure of the germinal center, together with re-entry of positively selected B cells back into the germinal center, will naturally implement such a schedule, thereby providing an anatomical basis for the efficiency of the germinal center reaction.     

CD4-deficient T helper cells are capable of supporting somatic hypermutation and affinity maturation of germinal center B cells

Collaborative interactions between B lymphocytes and CD4+ helper T cells are necessary for the induction of Ab responses to most protein Ag and for the generation of memory B cells in germinal centers. To study the role of the CD4 molecule in the germinal center response and in the development of B cell memory, we have investigated T helper function in the initiation and maturation of humoral immunity in CD4-deficient mice. In the absence of CD4+ T cells, immunization with thymus-dependent Ag was able to induce germinal center formation and Ig somatic hypermutation. In addition, Ag-driven affinity maturation and development of B cell memory were largely intact in CD4-deficient mice. Thus, CD4-deficient T helper cells are able to collaborate with Ag-activated B cells to elicit the germinal center reaction, switch on the mutational machinery, and deliver signals necessary for B cell memory development.     

Identification of a novel subpopulation of germinal center B cells characterized by expression of IgD and CD70

CD27, which belongs to the tumor necrosis-factor receptor family, is expressed on germinal center (GC) but not on naive B cells, suggesting an important function of this molecule in the regulation of the GC reaction. We described here the expression of CD70, which is the ligand for CD27. We observed that in most tonsils, CD70 is only expressed on part of the IgD^?, CD38^? B cell population, which have been described as memory B cells. However, in 10 % of the tonsils tested, CD70⁺ IgD⁺ GC were found. The CD70⁺ GC B cells were small cells that also expressed CD44 and CD39, but were CD10^? and CD38^?, suggesting that they represent very recent immigrants that are in the process of forming a GC. The concordant expression of CD27 and its ligand CD70 on this primordial subset of GC B cells suggests an important role for CD27/CD70 interaction at this stage of GC formation.