Proliferation Of Germinal Center Research Articles

Research progress of SREBP and its role in the pathogenesis of autoimmune rheumatic diseases.

Autoimmune rheumatic diseases comprise a group of immune-related disorders characterized by non-organ-specific inflammation. These diseases include systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), ankylosing spondylitis (AS), gout, among others. Typically involving the hematologic system, these diseases may also affect multiple organs and systems. The pathogenesis of autoimmune rheumatic immune diseases is complex, with diverse etiologies, all associated with immune dysfunction. The current treatment options for this type of disease are relatively limited and come with certain side effects. Therefore, the urgent challenge remains to identify novel therapeutic targets for these diseases. Sterol regulatory element-binding proteins (SREBPs) are basic helix-loop-helix-leucine zipper transcription factors that regulate the expression of genes involved in lipid and cholesterol biosynthesis. The expression and transcriptional activity of SREBPs can be modulated by extracellular stimuli such as polyunsaturated fatty acids, amino acids, glucose, and energy pathways including AKT-mTORC and AMP-activated protein kinase (AMPK). Studies have shown that SREBPs play roles in regulating lipid metabolism, cytokine production, inflammation, and the proliferation of germinal center B (GCB) cells. These functions are significant in the pathogenesis of rheumatic and immune diseases (Graphical abstract). Therefore, this paper reviews the potential mechanisms of SREBPs in the development of SLE, RA, and gout, based on an exploration of their functions.

Prolactin promotes proliferation of germinal center B cells, formation of plasma cells, and elevated levels of IgG3 anti-dsDNA autoantibodies.

Systemic lupus erythematosus (SLE) mainly affects females at reproductive age, which has been associated with hormones, such as prolactin (PRL). Different studies suggest that PRL exacerbates the clinical manifestations of SLE both in patients and in mouse models (e.g., the MRL/lpr strain), increasing the production of autoantibodies, which can be deposited as immune complexes and trigger inflammation and damage to different tissues. The objective of this work was to explore the potential mechanisms by which PRL increases the concentration of self-reactive antibodies in the MRL/lpr SLE model. To this end, we determined the role of PRL on the activation and proliferation of germinal center B cells (B-GCs) and their differentiation into antibody-secreting cells (ASCs). We show that the absolute number and percentage of B-GCs were significantly increased by PRL in vivo or upon in vitro treatment with anti-IgM and anti-CD40 antibodies and PRL. The augmented B-GC numbers correlated with enhanced proliferation, but we did not observe enhanced expression of CD80 and CD86 activation markers or the BCL6 transcription factor, arguing against a more effective differentiation. Nevertheless, we observed enhanced phosphorylation of STAT1, secretion of IL-6, expression of IRF4, numbers of ASCs, and levels of IgG3 antibodies directed against dsDNA. Altogether, these results support the hypothesis that a PRL-mediated expansion of B-GCs yields more self-reactive ASCs, potentially explaining the pathogenic immune complexes that steadily lead to tissue damage during SLE.

NF-κB Mutations in Germinal Center B-Cell Lymphomas: Relation to NF-κB Function in Normal B Cells.

Most B cell lymphomas arise from the oncogenic transformation of B cells that have undergone the germinal center (GC) reaction of the T cell-dependent immune response, where high-affinity memory B cells and plasma cells are generated. The high proliferation of GC B cells coupled with occasional errors in the DNA-modifying processes of somatic hypermutation and class switch recombination put the cell at a risk to obtain transforming genetic aberrations, which may activate proto-oncogenes or inactivate tumour suppressor genes. Several subtypes of GC lymphomas harbor genetic mutations leading to constitutive, aberrant activation of the nuclear factor-κB (NF-κB) signaling pathway. In normal B cells, NF-κB has crucial biological roles in development and physiology. GC lymphomas highjack these activities to promote tumour-cell growth and survival. It has become increasingly clear that the separate canonical and non-canonical routes of the NF-κB pathway and the five downstream NF-κB transcription factors have distinct functions in the successive stages of GC B-cell development. These findings may have direct implications for understanding how aberrant NF-κB activation promotes the genesis of various GC lymphomas corresponding to the developmentally distinct GC B-cell subsets. The knowledge arising from these studies may be explored for the development of precision medicine approaches aimed at more effective treatments of the corresponding tumours with specific NF-κB inhibitors, thus reducing systemic toxicity. We here provide an overview on the patterns of genetic NF-κB mutations encountered in the various GC lymphomas and discuss the consequences of aberrant NF-κB activation in those malignancies as related to the biology of NF-κB in their putative normal cellular counterparts.

Gammaherpesvirus-mediated repression reveals EWSR1 to be a negative regulator of B cell responses

The germinal center (GC) plays a central role in the generation of antigen-specific B cells and antibodies. Tight regulation of the GC is essential due to the inherent risks of tumorigenesis and autoimmunity posed by inappropriate GC B cell processes. Gammaherpesviruses such as Epstein-Barr virus (EBV) and murine gammaherpesvirus 68 (MHV68) utilize numerous armaments to drive infected naïve B cells, independent of antigen, through GC reactions to expand the latently infected B cell population and establish a stable latency reservoir. We previously demonstrated that the MHV68 microRNA (miRNA) mghv-miR-M1-7-5p represses host EWSR1 (Ewing sarcoma breakpoint region 1) to promote B cell infection. EWSR1 is a transcription and splicing regulator that is recognized for its involvement as a fusion protein in Ewing sarcoma. A function for EWSR1 in B cell responses has not been previously reported. Here, we demonstrate that 1) B cell-specific deletion of EWSR1 had no effect on generation of mature B cell subsets or basal immunoglobulin levels in naïve mice, 2) repression or ablation of EWSR1 in B cells promoted expansion of MHV68 latently infected GC B cells, and 3) B cell-specific deletion of EWSR1 during a normal immune response to nonviral antigen resulted in significantly elevated numbers of antigen-specific GC B cells, plasma cells, and circulating antibodies. Notably, EWSR1 deficiency did not affect the proliferation or survival of GC B cells but instead resulted in the generation of increased numbers of precursor GC B cells. Cumulatively, these findings demonstrate that EWSR1 is a negative regulator of B cell responses.

Mettl14-Mediated m6A Modification Is Essential for Germinal Center B Cell Response.

The germinal center (GC) response is essential for generating memory B and long-lived Ab-secreting plasma cells during the T cell-dependent immune response. In the GC, signals via the BCR and CD40 collaboratively promote the proliferation and positive selection of GC B cells expressing BCRs with high affinities for specific Ags. Although a complex gene transcriptional regulatory network is known to control the GC response, it remains elusive how the positive selection of GC B cells is modulated posttranscriptionally. In this study, we show that methyltransferase like 14 (Mettl14)-mediated methylation of adenosines at the position N 6 of mRNA (N 6-methyladenosine [m6A]) is essential for the GC B cell response in mice. Ablation of Mettl14 in B cells leads to compromised GC B cell proliferation and a defective Ab response. Interestingly, we unravel that Mettl14-mediated m6A regulates the expression of genes critical for positive selection and cell cycle regulation of GC B cells in a Ythdf2-dependent but Myc-independent manner. Furthermore, our study reveals that Mettl14-mediated m6A modification promotes mRNA decay of negative immune regulators, such as Lax1 and Tipe2, to upregulate genes requisite for GC B cell positive selection and proliferation. Thus, our findings suggest that Mettl14-mediated m6A modification plays an essential role in the GC B cell response.

IL-4-Producing Vγ1+/Vδ6+ γδ T Cells Sustain Germinal Center Reactions in Peyer's Patches of Mice.

The mucosal immune system is the first line of defense against pathogens. Germinal centers (GCs) in the Peyer’s patches (PPs) of the small intestine are constantly generated through stimulation of the microbiota. In this study, we investigated the role of γδ T cells in the GC reactions in PPs. Most γδ T cells in PPs localized in the GCs and expressed a TCR composed of Vγ1 and Vδ6 chains. By using mice with partial and total γδ T cell deficiencies, we found that Vγ1+/Vδ6+ T cells can produce high amounts of IL-4, which drives the proliferation of GC B cells as well as the switch of GC B cells towards IgA. Therefore, we conclude that γδ T cells play a role in sustaining gut homeostasis and symbiosis via supporting the GC reactions in PPs.

Toll-Like Receptor 4 Regulates Rabies Virus-Induced Humoral Immunity through Recruitment of Conventional Type 2 Dendritic Cells to Lymph Organs.

Rabies, caused by rabies virus (RABV), is fatal to both humans and animals around the world. Effective clinical therapy for rabies has not been achieved, and vaccination is the most effective means of preventing and controlling rabies. Although different vaccines, such as live attenuated and inactivated vaccines, can induce different immune responses, different expressions of pattern recognition receptors (PRRs) also cause diverse immune responses. Toll-like receptor 4 (TLR4) is a pivotal PRR that induces cytokine production and bridges innate and adaptive immunity. Importantly, TLR4 recognizes various virus-derived pathogen-associated molecular patterns (PAMPs) and virus-induced damage-associated molecular patterns (DAMPs), usually leading to the activation of immune cells. However, the role of TLR4 in the humoral immune response induced by RABV has not yet been revealed. Based on TLR4-deficient (TLR4-/-) and wild-type (WT) mouse models, we report that TLR4-dependent recruitment of the conventional type 2 dendritic cells (CD8α- CD11b+ cDC2) into secondary lymph organs (SLOs) is critical for antigen presentation. cDC2-initiated differentiation of follicular helper T (Tfh) cells promotes the proliferation of germinal center (GC) B cells, the formation of GCs, and the production of plasma cells (PCs), all of which contribute to the production of RABV-specific IgG and virus-neutralizing antibodies (VNAs). Collectively, our work demonstrates that TLR4 is necessary for the recruitment of cDC2 and for the induction of RABV-induced humoral immunity, which is regulated by the cDC2-Tfh-GC B axis. IMPORTANCE Vaccination is the most efficient method to prevent rabies. TLR4, a well-known immune sensor, plays a critical role in initiating innate immune response. Here, we found that TLR4-deficient (TLR4-/-) mice suppressed the induction of humoral immune response after immunization with rabies virus (RABV), including reduced production of VNAs and RABV-specific IgG compared to that occurred in wild-type (WT) mice. As a consequence, TLR4-/- mice exhibited higher mortality than that of WT mice after challenge with virulent RABV. Importantly, further investigation found that TLR4 signaling promoted the recruitment of cDC2 (CD8α+ CD11b-), a subset of cDCs known to induce CD4+ T-cell immunity through their MHC-II presentation machinery. Our results imply that TLR4 is indispensable for an efficient humoral response to rabies vaccine, which provides new insight into the development of novel rabies vaccines.

A Posttranscriptional Pathway of CD40 Ligand mRNA Stability Is Required for the Development of an Optimal Humoral Immune Response

CD40 ligand (CD40L) mRNA stability is dependent on an activation-induced pathway that is mediated by the binding complexes containing the multifunctional RNA-binding protein, polypyrimidine tract-binding protein 1 (PTBP1) to a 3' untranslated region of the transcript. To understand the relationship between regulated CD40L and the requirement for variegated expression during a T-dependent response, we engineered a mouse lacking the CD40L stability element (CD40LΔ5) and asked how this mutation altered multiple aspects of the humoral immunity. We found that CD40LΔ5 mice expressed CD40L at 60% wildtype levels, and lowered expression corresponded to significantly decreased levels of T-dependent Abs, loss of germinal center (GC) B cells and a disorganized GC structure. Gene expression analysis of B cells from CD40LΔ5 mice revealed that genes associated with cell cycle and DNA replication were significantly downregulated and genes linked to apoptosis upregulated. Importantly, somatic hypermutation was relatively unaffected although the number of cells expressing high-affinity Abs was greatly reduced. Additionally, a significant loss of plasmablasts and early memory B cell precursors as a percentage of total GL7+ B cells was observed, indicating that differentiation cues leading to the development of post-GC subsets was highly dependent on a threshold level of CD40L. Thus, regulated mRNA stability plays an integral role in the optimization of humoral immunity by allowing for a dynamic level of CD40L expression on CD4 T cells that results in the proliferation and differentiation of pre-GC and GC B cells into functional subsets.

Activation-dependent post-transcriptional regulation of CD40L mediates B cell development and survival in germinal centers

Abstract We have described a posttranscriptional pathway of induced mRNA stability that occurs at late times of T cell activation and is engaged by the binding of a polypyrimidine tract-binding protein (PTBP1) complex to the 3′UTR of the CD40L transcript. We explored the in vivo role of this pathway by generating a mouse bearing a deletion of the CD40L stability element (termed CD40LΔ5) and found that Tfh cells harboring the stability defect expressed approximately 60% of WT CD40L. Importantly, this decrease in CD40L corresponded to a poorly elaborated germinal center (GC) response which included significantly decreased levels of switched antibodies, antibody-secreting cells, GL7+ B cells and differentiated GC B cell subsets. In contrast, there was little difference in either somatic hypermutation or affinity maturation between B cells from WT compared to CD40LD5 mice. Notably, both the number and percentage of early memory B cells and plasmablasts were significantly decreased indicating that CD40L expression linked to mRNA stability was critical for B cell differentiation. To understand the impact of this stability pathway on gene expression, CD19+ B cells from CD40LD5 immunized mice were transcriptionally profiled using RNAseq and pathways associated with cell survival and proliferation were downregulated and apoptotic pathways upregulated compared to WT B cells. Importantly, the level of AID mRNA was unchanged whereas c-myc expression was significantly reduced in GL7+ B cells. Together these findings reveal that the CD40L stability element plays a critical role in regulating CD40L expression in Tfh cells, which in turn supports the optimal proliferation and cell survival of high affinity GC B cells and the differentiation of B cell subsets.

Gammaherpesvirus Usurps Host IL-17 Signaling To Support the Establishment of Chronic Infection.

Gammaherpesviruses establish lifelong infection and are associated with a variety of cancers, including B cell lymphomas. These viruses manipulate the B cell differentiation process to establish lifelong infection in memory B cells. Specifically, gammaherpesviruses infect naive B cells and promote entry of both infected and uninfected naive B cells into germinal centers, where the virus usurps rapid proliferation of germinal center B cells to exponentially increase its cellular latent reservoir. In addition to facilitating the establishment of latent infection, germinal center B cells are thought to be the target of viral transformation. In this study, we have uncovered a novel proviral role of host interleukin 17A (IL-17A), a well-established antibacterial and antifungal factor. Loss of IL-17A signaling attenuated the establishment of chronic gammaherpesvirus infection and gammaherpesvirus-driven germinal center response in a route of inoculation-dependent manner. Further, IL-17A treatment directly supported gammaherpesvirus reactivation and de novo lytic infection. This study is the first demonstration of a multifaceted proviral role of IL-17 signaling.IMPORTANCE Gammaherpesviruses establish lifelong infections in a majority of humans and are associated with B cell lymphomas. IL-17A is a host cytokine that plays a well-established role in the clearance of bacterial and fungal infections; however, the role of IL-17A in viral infections is poorly understood. In this study, we show that IL-17A signaling promoted the establishment of chronic gammaherpesvirus infection following the mucosal route of infection, viral lytic replication, and reactivation from latency. Thus, our study unveils a novel proviral role of IL-17A signaling in gammaherpesvirus infection.

A Phase 2, Open-Label, Multicenter Study of Tazemetostat in Combination with Rituximab for the Treatment of Relapsed or Refractory Follicular Lymphoma

Background: Patients with follicular lymphoma (FL) who do not achieve a response after 2 or more prior lines of systemic therapy have a poor prognosis when treated with salvage chemotherapy alone or PI3K inhibitors. Enhancer of zeste homolog 2 (EZH2) is a histone methyltransferase that supports germinal center (GC) formation and suspends differentiation during B-cell development by silencing genes that limit proliferation and promote exit from the GC. Throughout the pathogenesis of FL, EZH2 plays a consistent underlying role in maintaining the GC and B-cell proliferation, regardless of the oncogenic drivers. Dysregulation of EZH2 or gain-of-function mutations in EZH2 can lead to accumulation of malignant B cells and may contribute to the development of FL. Tazemetostat, a first-in-class oral EZH2 inhibitor, recently gained approval by the US Food and Drug Administration in patients with relapsed or refractory (R/R) FL after demonstrating single-agent, antitumor activity in patients with mutant (MT) or wild-type (WT) EZH2 R/R FL. Here we examine the efficacy and safety of tazemetostat in combination with rituximab for the treatment of R/R FL. Study Design and Methods: This trial is a phase 2, single-arm, open-label, multicenter study of tazemetostat in combination with rituximab in patients with R/R FL who have received at least 2 prior lines of systemic therapy, including an anti-CD20-based regimen. Patients eligible for inclusion are aged ≥18 years with grade 1 to 3A FL who have met Groupe d'Etude des Lymphomes Folliculaires (GELF) criteria to receive treatment, have an Eastern Cooperative Oncology Group (ECOG) score ≤2, have >5.0 x 109/L circulating malignant cells, and have not received any prior treatment with EZH2 inhibitors. Patients with transformed FL, a history of clinically significant gastrointestinal conditions, or any uncontrolled illness are excluded from this study. EZH2 mutation testing will be performed during patient screening. Patients will receive tazemetostat 800 mg by mouth twice daily beginning on cycle 1 day 1 for continuous 28-day cycles until the end of cycle 24, for a total of 24 months of therapy. Patients will also receive rituximab 375 mg/m2 intravenously (IV) on cycle 1 day 1, then 375 mg/m2 IV or 1400 mg subcutaneously on days 8, 15, and 22 of cycle 1, and on day 1 of cycles 3, 4, 5, and 6, for a total of 8 doses of rituximab. The primary endpoint is the objective response rate (ORR; the proportion of patients with complete or partial response) in patients with WT EZH2. Key secondary endpoints include median progression free survival (PFS) in patients with WT EZH2; median PFS in all patients, regardless of mutational status; ORR in patients with MT EZH2; efficacy outcomes in rituximab-refractory patients; and incidence of adverse events. Efficacy and safety analyses will be performed on all patients who receive ≥1 dose of study drug. The evaluation of ORR will be based on Lugano 2014 response criteria and will be presented with corresponding 2-sided Clopper-Pearson 95% confidence intervals. The Kaplan-Meier method will be used to estimate PFS. Survival follow-up will be done following the study treatment period every 6 months for 2 years or until disease progression or death for all patients who complete the 24 months of tazemetostat therapy. Disclosures Patel: Adaptive Biotechnologies, AstraZeneca, Pharmacyclics, Janssen, Genentech, Celgene/BMS, BeiGene, Kite: Consultancy. Pagel:Gilead, Pharmacyclics LLC, an AbbVie Company, and AstraZeneca: Consultancy.

Abstract PO-08: Understanding the properties and oncogenic mechanisms of EZH2 Y641 mutations in lymphoma

Abstract EZH2 (Enhancer of Zeste Homolog 2) is the catalytic component of the Polycomb Repressive Complex group 2 (PRC2), which establishes the repressive epigenetic mark histone 3 lysine 27 trimethylation (H3K27me3), resulting in silencing of gene expression. EZH2 was originally identified as a tumor suppressor since loss-of-function events were observed in myelodysplastic syndrome, acute myeloid, and T-cell leukemias. However, next-generation sequencing identified recurrent activating point mutations at tyrosine residue 641 (Y641) in 25% of germinal center diffuse large B-cell lymphoma and 15% of follicular lymphomas, suggesting that EZH2 also functions as an oncogene in a cell type-dependent manner. Using a faithful genetically engineered mouse model, we previously demonstrated that the Ezh2Y641F mutation drives formation of B-cell lymphoma as a single event and in cooperation with Bcl2 amplification or p53 loss. Unexpectedly, at the chromatin level, expression of Ezh2Y641F did not monotonically increase abundance of global H3K27me3 but rather resulted in redistribution of this mark across the genome, exhibiting loss of H3K27me3 at many loci, with direct effects on transcription. Others have shown that EZH2 mediates germinal center proliferation via repression of p21 and cooperation with Bcl6; however, given the global effect of Ezh2Y641F on chromatin, the oncogenic mechanisms of these mutations remain underexplored. These include the timing of the mutation during hematopoietic development, its role during differentiation, and the oncogenic activity of downstream targets. In order to investigate the effect of Ezh2Y641 mutations on hematopoietic development and differentiation, we used Cre alleles to drive expression of the mutant protein at different stages of hematopoietic development. Our data demonstrate that expression of Ezh2Y641 in early B cells is sufficient to drive oncogenic transformation. However, expression of Ezh2Y641 in hematopoietic stem cell (HSC) is not sufficient to drive oncogenic transformation despite the presence of mature healthy B cells. Additionally, expression of Ezh2Y641F in HSCs results in loss of self-renewal, differentiation bias towards the lymphoid lineages, and a partial block at the pre-pro B-cell stage. With regards to direct downstream targets, we identified upregulation of several HoxC cluster genes in Ezh2Y641F-mutant B cells prior to transformation. Upregulation of these genes is mediated via loss of H3K27me3 at the HoxC cluster and focal gains of H3K27 acetylation (H3K27ac). Overall, our findings underline the complicated biology and oncogenic activity of EZH2Y641 mutations in lymphoma, shed light on the effect of these mutations during hematopoietic development, and underscore some of the consequences of the paradoxical loss of H3K27me3 at certain loci. Citation Format: Samantha J. Nixon, Sarah Zimmerman, Jeremy M. Simon, George P. Souroullas. Understanding the properties and oncogenic mechanisms of EZH2 Y641 mutations in lymphoma [abstract]. In: Proceedings of the AACR Virtual Meeting: Advances in Malignant Lymphoma; 2020 Aug 17-19. Philadelphia (PA): AACR; Blood Cancer Discov 2020;1(3_Suppl):Abstract nr PO-08.

PHF14 is required for germinal center B cell development

Germinal centers (GCs), which are the site of antibody diversification and affinity maturation, are vitally important for humoral immunity. GC B cell proliferation is essentially for these processes by providing enough templates for somatic hypermutation (SHM) and serving as a critical mechanism of positive selection. In the current study, we found a significant reduction of GC response in the spleens of GC B cell specific PHF14 knockout (PHF14GCB KO) mice compared with the wild-type control (PHF14GCB WT) when the mice were challenged with SRBCs or lymphocytic choriomeningitis virus. We also demonstrated that PHF14 did not affect the cell survival of GC B cells, but regulated the proliferation of GC B cells. In addition, PHF14 suppressed the expression of Cdkn1a (p21) though regulating the level of H3K4me3 to control the proliferation of GC B cells. Collectively, our data suggest that PHF14 plays an important role in the process of germinal center formation by regulating GC B cell proliferation in spleen.

Primary follicular lymphoma of buccal mucosa: A case report

AbstractFollicular lymphoma (FL) is a non‐Hodgkin lymphoma subtype arising from the neoplastic proliferation of germinal center B‐cells. Typically, FL occurs in the lymph nodes, and its solitary primary manifestation in the oral cavity (OFL) is rare. Here we describe a case of primary FL of the buccal mucosa in a 61‐year‐old woman; the prognosis following treatment with chemotherapy and radiotherapy was good. A literature review revealed that the oral cavity might be a key organ with high probability of having early‐stage FL. This report highlights the OFL features and importance of proper diagnosis and timely treatment to improve prognosis.

Activation-dependent post-transcriptional regulation of CD40L mediates B cell development and survival in germinal centers

Abstract We have previously described a post-transcriptional pathway of induced mRNA stability that occurs at late times of T cell activation and is engaged by the binding of polypyrimidine tract-binding protein (PTBP1) complex to the 3′ UTR of the CD40L transcript. We recently explored the in vivo role of this pathway by generating a genetically modified mouse (CD40LΔ5) bearing a deletion of the PTBP1 stability element. We found that the CD40LΔ5 mice display a dysfunctional germinal center (GC) response including significantly decreased levels of isotype switched antibodies, antibody-secreting cells, memory B cells and GL7+ GC B cells. To extend our earlier findings we measured affinity maturation of antibodies in response to the hapten NP and found a loss of high affinity binding that corresponded to reduced numbers of targeted VH mutations known to be associated with high affinity binding. However, there were no discernible differences in the overall number of mutations across the VH segment, suggesting that the CD40LΔ5 pathway may have a greater effect on the selection and/or expansion of high-affinity B cells rather than on the somatic hypermutation (SHM) in general. To identify how the CD40L mRNA stability pathway impacted B cells during an immune response, CD19+ B cells from immunized mice were transcriptionally profiled using RNAseq. Expression of genes associated with cell survival and proliferation were found to be down-regulated and apoptotic genes up-regulated in CD40LΔ5 B cells compared to WT cells. Together these finding are consistent with the Δ5 stability element playing a critical role in the proliferation and cell survival of high affinity GC B cells through a pathway of enhanced expression of CD40L in CD4 T cells.

Washed microbiota transplantation vs. manual fecal microbiota transplantation: clinical findings, animal studies and in vitro screening

Fecal microbiota transplantation (FMT) by manual preparation has been applied to treat diseases for thousands of years. However, this method still endures safety risks and challenges the psychological endurance and acceptance of doctors, patients and donors. Population evidence showed the washed microbiota preparation with microfiltration based on an automatic purification system followed by repeated centrifugation plus suspension for three times significantly reduced FMT-related adverse events. This washing preparation makes delivering a precise dose of the enriched microbiota feasible, instead of using the weight of stool. Intraperitoneal injection in mice with the fecal microbiota supernatant obtained after repeated centrifugation plus suspension for three times induced less toxic reaction than that by the first centrifugation following the microfiltration. The toxic reactions that include death, the change in the level of peripheral white blood cells, and the proliferation of germinal center in secondary lymphoid follicles in spleen were noted. The metagenomic next-generation sequencing (NGS) indicated the increasing types and amount of viruses could be washed out during the washing process. Metabolomics analysis indicated metabolites with pro-inflammatory effects in the fecal microbiota supernatant such as leukotriene B4, corticosterone, and prostaglandin G2 could be removed by repeated washing. Near-infrared absorption spectroscopy could be served as a rapid detection method to control the quality of the washing-process. In conclusion, this study for the first time provides evidence linking clinical findings and animal experiments to support that washed microbiota transplantation (WMT) is safer, more precise and more quality-controllable than the crude FMT by manual.

Germinal center organization mediated by T-bet dependent expression of CXCR3 and CCR6

Abstract The germinal center (GC) is composed of distinct regions with proliferation and affinity maturation of GC B cells (GCB) occurring in the dark zone (DZ) and antigen-mediated selection and commitment of the long-lived plasma cell (LL-PCs) precursors occurring in the light zone (LZ). Despite the key role for GCs in establishing enduring humoral immunity, we know little about the dynamics of the GCB cell response. We showed that the transcription factor T-bet is expressed by GCB cells and that B cell intrinsic T-bet is required for the LL-PC response following influenza (flu) infection. To test whether the loss of LL-PCs in these mice was due to a role for T-bet in regulating the GCB response, we infected 50:50 Tbx21−/−: pepboy chimeric mice with flu and enumerated GCB cells. We found that Tbx21−/− B cells were overrepresented in the GC relative to the pepboy cells and that Tbx21−/− GCB cells were enriched in the LZ. Partitioning of GCB cells in the LZ/DZ is regulated by chemokines and we showed that T-bet controls transcription of two chemokine receptors, CXCR3 and CCR6, which are expressed by GCB cells. Using 50:50 Tbx21−/−: pepboy chimeras, we tested whether T-bet regulates GCB cell positioning by inducing CXCR3 and repressing CCR6. We observed that the CCR6+ GCB cell subset, which is known to localize in the LZ, was very enriched in Tbx21−/− GCB cells. By contrast, the CXCR3+ GCB subset, which was dominated by WT cells, was enriched in the DZ. To determine the role for CXCR3 in GCB cell localization, we infected 50:50 Cxcr3−/− :pepboy chimeras and found that the Cxcr3−/− GCB cells are enriched in the LZ. Therefore, T-bet regulates GCB cell localization and potentially the dynamics of the GC response by controlling CXCR3 and CCR6 expression.

IL-21 Is Increased in Nasal Polyposis and after Stimulation with Staphylococcus aureus Enterotoxin B

Background: Chronic rhinosinusitis with nasal polyposis (CRSwNP) is an inflammatory disease associated with lymphoid aggregates and local IgE production related to Staphylococcus aureus enterotoxins. T-follicular helper cells and their effector cytokine interleukin (IL)-21 play an important role in germinal center proliferation. Methods: IL-21 was determined on the mRNA level by qPCR in nasal tissue of 3 groups of patients: control (n = 17), chronic rhinosinusitis without nasal polyposis (CRSsNP; n = 23), and CRSwNP (n = 35). The expression of IL-21 by CD4+ T cells was analyzed in tissue at baseline and after 24-h stimulation of tissue fragments with S. aureus enterotoxin B (SEB) using flow cytometry. Finally, human nasal IL-21+CXCR5+CD4+ T cells were isolated and coincubated with human blood naive B cells to investigate their functionality. Results: IL-21 mRNA expression was increased in the CRSwNP group (p < 0.05) compared to the control group, and B-cell lymphoma-6 and B-lymphocyte-induced maturation protein-1 were upregulated in CRSwNP versus CRSsNP. Furthermore, SEB was able to increase IL-21 mRNA expression significantly (p < 0.01) in nasal polyps. Flow cytometry revealed that the source of IL-21 was predominantly CD4+ T cells and that IL-21+CD4+ T cells were significantly increased in polyp tissue and further increased after SEB stimulation. Finally, tissue CXCR5+CD4+ T cells derived from nasal polyp tissue were able to induce maturation of human naive B cells. Conclusions: IL-21- and IL-21-producing CD4+ T cells were increased in CRSwNP. In addition, SEB induced an increase in IL-21 and IL-21+CD4+ T cells, suggesting that S. aureus can modulate the function of Tfh cells in nasal polyps. We speculate that T-follicular helper cells and IL-21 are important in the pathophysiology of CRSwNP.

MTOR Promotes Antiviral Humoral Immunity by Differentially Regulating CD4 Helper T Cell and B Cell Responses.

mTOR is a serine/threonine kinase involved in a variety of cellular activities. Although its specific inhibitor, rapamycin, is currently used as an immunosuppressive drug in transplant patients, it has been reported that rapamycin can also stimulate pathogen-specific cellular immunity in certain circumstances. However, whether and how mTOR regulates humoral immunity are not well understood. Here we found that rapamycin treatment predominantly inhibited GC B cell responses during viral infection and that this led to biased helper CD4 T cell differentiation as well as impaired antibody responses. These findings suggest that inhibition of B cell responses by rapamycin may play an important role in regulation of allograft-specific antibody responses to prevent organ rejection in transplant recipients. Our results also show that consideration of antibody responses is required in cases where rapamycin is used to stimulate vaccine-induced immunity.

Mitochondrial reactive oxygen species suppress humoral immune response through reduction of CD19 expression in B cells in mice

Reactive oxygen species (ROS) are implicated in the modulation of diverse processes including immune responses. To evaluate the effects of metabolic ROS produced by mitochondria on B-cell function and development, we created transgenic (Tg) mice expressing a phosphorylation-defective mutant of succinate dehydrogenase A in B cells (bSDHAY215F ). Splenic B cells in male, but not female, bSDHAY215F mice produced three times more ROS than those in the control mice, and had decreased production of IgM, IgG1 , and IgG3 , and affinity maturation of IgG1 against T-cell-dependent antigens. Following immunization, the male bSDHAY215F mice further displayed suppressed germinal center (GC) formation, and proliferation of GC B cells. Signaling analysis revealed defects in the intrinsic BCR responses, such as activation of Lyn, Btk, and PLCγ2, thus resulting in reduced intracellular Ca2+ mobilization. Notably, the expression levels of B-cell co-receptor CD19 and its interaction with Lyn after BCR ligation were significantly reduced in B cells from male bSDHAY215F mice. These results suggest that mitochondrial ROS suppress humoral immune responses through reduction of CD19 expression and resultant BCR signaling in B cells. Therefore, B-cell immunity may be more labile to oxidative stress in male mice than in female mice.