Effectors and memories: Bcl-6 and Blimp-1 in T and B lymphocyte differentiation

Continuous time Bayesian networks identify Prdm1 as a negative regulator of TH17 cell differentiation in humans

T helper 17 (TH17) cells represent a pivotal adaptive cell subset involved in multiple immune disorders in mammalian species. Deciphering the molecular interactions regulating TH17 cell differentiation is particularly critical for novel drug target discovery designed to control maladaptive inflammatory conditions. Using continuous time Bayesian networks over a time-course gene expression dataset, we inferred the global regulatory network controlling TH17 differentiation. From the network, we identified the Prdm1 gene encoding the B lymphocyte-induced maturation protein 1 as a crucial negative regulator of human TH17 cell differentiation. The results have been validated by perturbing Prdm1 expression on freshly isolated CD4(+) naïve T cells: reduction of Prdm1 expression leads to augmentation of IL-17 release. These data unravel a possible novel target to control TH17 polarization in inflammatory disorders. Furthermore, this study represents the first in vitro validation of continuous time Bayesian networks as gene network reconstruction method and as hypothesis generation tool for wet-lab biological experiments.

Follicular regulatory T cells repress cytokine production by follicular helper T cells and optimize IgG responses in mice

Follicular helper T (Tfh) cells provide crucial help to germinal center B (GCB) cells for proper antibody production, and a specialized subset of regulatory T cells, follicular regulatory T (Tfr) cells, modulate this process. However, Tfr-cell function in the GC is not well understood. Here, we define Tfr cells as a CD4(+) Foxp3(+) CXCR5(hi) PD-1(hi) CD25(low) TIGIT(high) T-cell population. Furthermore, we have used a novel mouse model ("Bcl6FC") to delete the Bcl6 gene in Foxp3(+) T cells and thus specifically deplete Tfr cells. Following immunization, Bcl6FC mice develop normal Tfh- and GCB-cell populations. However, Bcl6FC mice produce altered antigen-specific antibody responses, with reduced titers of IgG and significantly increased IgA. Bcl6FC mice also developed IgG antibodies with significantly decreased avidity to antigen in an HIV-1 gp120 "prime-boost" vaccine model. In an autoimmune lupus model, we observed strongly elevated anti-DNA IgA titers in Bcl6FC mice. Additionally, Tfh cells from Bcl6FC mice consistently produce higher levels of Interferon-γ, IL-10 and IL-21. Loss of Tfr cells therefore leads to highly abnormal Tfh-cell and GCB-cell responses. Overall, our study has uncovered unique regulatory roles for Tfr cells in the GC response.

Design of nanomaterial based systems for novel vaccine development

With lower cell toxicity and higher specificity, novel vaccines have been greatly developed and applied to emerging infectious and chronic diseases. However, due to problems associated with low immunogenicity and complicated processing steps, the development of novel vaccines has been limited. With the rapid development of bio-technologies and material sciences, nanomaterials are playing essential roles in novel vaccine design. Incorporation of nanomaterials is expected to improve delivery efficiency, to increase immunogenicity, and to reduce the administration dosage. The purpose of this review is to discuss the employment of nanomaterials, including polymeric nanoparticles, liposomes, virus-like particles, peptide amphiphiles micelles, peptide nanofibers and microneedle arrays, in vaccine design. Compared to traditional methods, vaccines made from nanomaterials display many appealing benefits, including precise stimulation of immune responses, effective targeting to certain tissue or cells, and desirable biocompatibility. Current research suggests that nanomaterials may improve our approach to the design and delivery of novel vaccines.

Genome-wide Analysis Identifies Bcl6-Controlled Regulatory Networks during T Follicular Helper Cell Differentiation

T follicular helper (Tfh) cell is a unique T cell subset specialized in promoting humoral immunity. B-cell lymphoma 6 protein (Bcl6) has been identified as an obligatory transcription factor in Tfh cells; however, the molecular mechanism underlying Bcl6 function remains largely unknown. Here, we defined Bcl6 target genes in Tfh cells by analyzing genome-wide Bcl6 occupancy together with transcriptome profiling. With consensus sequences being different from those in Th9, B cells, and macrophages, Bcl6 binding in Tfh cell was closely associated with a decrease in 5-hydroxymethylcytosine (5hmC). Importantly, Bcl6 promoted Tfh cell differentiation through antagonizing IL-7R (CD127)/signal transducer and activator of transcription (STAT) 5 axis; deletion of the Bcl6 gene in T cells resulted in enhanced IL-7R-STAT5 signaling and substantial expansion of CD127(hi) non-Tfh cells. Thus, our study systemically examines Bcl6-controlled regulatory networks and provides important insights into Bcl6's biological functions in Tfh cells.

B Cells Negatively Regulate the Establishment of CD49b(+)T-bet(+) Resting Memory T Helper Cells in the Bone Marrow

During an immune reaction, some antigen-experienced CD4 T cells relocate from secondary lymphoid organs (SLOs) to the bone marrow (BM) in a CD49b-dependent manner and reside and rest there as professional memory CD4 T cells. However, it remains unclear how the precursors of BM memory CD4 T cells are generated in the SLOs. While several studies have so far shown that B cell depletion reduces the persistence of memory CD4 T cells in the spleen, we here show that B cell depletion enhances the establishment of memory CD4 T cells in the BM and that B cell transfer conversely suppresses it. Interestingly, the number of antigen-experienced CD4 T cells in the BM synchronizes the number of CD49b⁺T-bet⁺ antigen-experienced CD4 T cells in the spleen. CD49b⁺T-bet⁺ antigen-experienced CD4 T cells preferentially localize in the red pulp area of the spleen and the BM in a T-bet-independent manner. We suggest that B cells negatively control the generation of CD49b⁺T-bet⁺ precursors of resting memory CD4 T cells in the spleen and may play a role in bifurcation of activated effector and resting memory CD4 T cell lineages.

Natural killer group 2D and CD28 receptors differentially activate mammalian/mechanistic target of rapamycin to alter murine effector CD8+ T-cell differentiation

Memory CD8+ T cells are an essential component of anti-tumour and anti-viral immunity. Activation of the mammalian/mechanistic target of rapamycin (mTOR) pathway has been implicated in regulating the differentiation of effector and memory T cells. However, the mechanisms that control mTOR activity during immunity to tumours and infections are not well known. Activation of co-stimulatory receptors, including CD28 and natural killer group 2D (NKG2D), activate phosphatidylinositol-3 kinase and subsequently may activate the mTOR pathway in CD8+ T cells. This study compared the activation of the mTOR signalling pathway after co-stimulation through CD28 or NKG2D receptors in murine effector CD8+ T cells. Compared with CD28 co-stimulation, activation through CD3 and NKG2D receptors had weaker activation of mTORc1, as shown by decreased phosphorylation of mTORc1 targets S6K1, ribosomal protein S6 and eukaryotic initiation factor 4E binding protein 1. NKG2D co-stimulation also showed increased gene expression of tuberous sclerosis protein 2, a negative regulator of mTORc1, whereas CD28 co-stimulation increased gene expression of Ras homologue enriched in brain, an activator of mTORc1, and hypoxia-inducible factor-1α and vascular endothelial growth factor-α, pro-angiogenic factors downstream of mTORc1. Strong mTORc1 activation in CD28-co-stimulated cells also increased expression of transcription factors that support effector cell differentiation, namely T-bet, B lymphocyte-induced maturation protein (BLIMP-1), interferon regulatory factor 4, and inhibitor of DNA binding 2, whereas low levels of mTORc1 activation allowed for the expression of Eomes, B-cell lymphoma 6 (BCL6), and inhibitor of DNA binding 3 during NKG2D stimulation, and increased expression of memory markers CD62 ligand and CD127. These data show that compared with CD28, co-stimulation through the NKG2D receptor leads to the differential activation of the mTOR signalling pathway and potentially supports memory CD8+ T-cell differentiation.

IL-7 signalling represses Bcl-6 and the TFH gene program

The transcriptional repressor Bcl-6 is linked to the development of both CD4⁺ T follicular helper (T_FH) and central memory T (T_CM) cells. Here, we demonstrate that in response to decreased IL-2 signalling, T helper 1 (T_H1) cells upregulate Bcl-6 and co-initiate T_FH- and T_CM-like gene programs, including expression of the cytokine receptors IL-6Rα and IL-7R. Exposure of this potentially bi-potent cell population to IL-6 favours the T_FH gene program, whereas IL-7 signalling represses T_FH-associated genes including Bcl6 and Cxcr5, but not the T_CM-related genes Klf2 and Sell. Mechanistically, IL-7-dependent activation of STAT5 contributes to Bcl-6 repression. Importantly, antigen-specific IL-6Rα⁺IL-7R⁺ CD4⁺ T cells emerge from the effector population at late time points post influenza infection. These data support a novel role for IL-7 in the repression of the T_FH gene program and evoke a divergent regulatory mechanism by which post-effector T_H1 cells may contribute to long-term cell-mediated and humoral immunity.

It remains incompletely understood how cytokines shape T_H1 cell differentiation to central memory T (T_CM) and follicular T helper (T_FH) cells. Here the authors show that T_H1 cells can co-initiate the expression of both T_FH and T_CM gene programs and that IL-7 signalling represses T_FH-associated but not T_CM-associated genes.

High-dimensional immune profiling of total and rotavirus VP6-specific intestinal and circulating B cells by mass cytometry

In-depth phenotyping of human intestinal antibody secreting cells (ASCs) and their precursors is important for developing improved mucosal vaccines. We used single-cell mass cytometry to simultaneously analyze 34 differentiation and trafficking markers on intestinal and circulating B cells. In addition, we labeled rotavirus (RV) double-layered particles with a metal isotope and characterized B cells specific to the RV VP6 major structural protein. We describe the heterogeneity of the intestinal B-cell compartment, dominated by ASCs with some phenotypic and transcriptional characteristics of long-lived plasma cells. Using principal component analysis, we visualized the phenotypic relationships between major B-cell subsets in the intestine and blood, and revealed that IgM(+) memory B cells (MBCs) and naive B cells were phenotypically related as were CD27(-) MBCs and switched MBCs. ASCs in the intestine and blood were highly clonally related, but associated with distinct trajectories of phenotypic development. VP6-specific B cells were present among diverse B-cell subsets in immune donors, including naive B cells, with phenotypes representative of the overall B-cell pool. These data provide a high dimensional view of intestinal B cells and the determinants regulating humoral memory to a ubiquitous, mucosal pathogen at steady-state.

IgG-Immune Complexes Promote B Cell Memory by Inducing BAFF

Memory B cell responses are vital for protection against infections but must also be regulated to prevent autoimmunity. Cognate T cell help, somatic hypermutation, and affinity maturation within germinal centers (GCs) are required for high-affinity memory B cell formation; however, the signals that commit GC B cells to the memory pool remain unclear. In this study, we identify a role for IgG-immune complexes (ICs), FcγRs, and BAFF during the formation of memory B cells in mice. We found that early secretion of IgG in response to immunization with a T-dependent Ag leads to IC-FcγR interactions that induce dendritic cells to secrete BAFF, which acts at or upstream of Bcl-6 in activated B cells. Loss of CD16, hematopoietic cell-derived BAFF, or blocking IC:FcγR regions in vivo diminished the expression of Bcl-6, the frequency of GC and memory B cells, and secondary Ab responses. BAFF also contributed to the maintenance and/or expansion of the follicular helper T cell population, although it was dispensable for their formation. Thus, early Ab responses contribute to the optimal formation of B cell memory through IgG-ICs and BAFF. Our work defines a new role for FcγRs in GC and memory B cell responses.

IFN-γ and IL-21 Double Producing T Cells Are Bcl6-Independent and Survive into the Memory Phase in Plasmodium chabaudi Infection

CD4 T cells are required to fight malaria infection by promoting both phagocytic activity and B cell responses for parasite clearance. In Plasmodium chabaudi infection, one specific CD4 T cell subset generates anti-parasitic IFN-γ and the antibody-promoting cytokine, IL-21. To determine the lineage of these multifunctional T cells, we followed IFN-γ⁺ effector T cells (Teff) into the memory phase using Ifng-reporter mice. While Ifng⁺ Teff expanded, the level of the Th1 lineage-determining transcription factor T-bet only peaked briefly. Ifng⁺ Teff also co-express ICOS, the B cell area homing molecule CXCR5, and other Tfh lineage-associated molecules including Bcl6, the transcription factor required for germinal center (GC) T follicular helper cells (Tfh) differentiation. Because Bcl6 and T-bet co-localize to the nucleus of Ifng⁺ Teff, we hypothesized that Bcl6 controls the Tfh-like phenotype of Ifng⁺ Teff cells in P. chabaudi infection. We first transferred Bcl6-deficient T cells into wildtype hosts. Bcl6-deficient T cells did not develop into GC Tfh, but they still generated CXCR5⁺IFN-γ⁺IL-21⁺IL-10⁺ Teff, suggesting that this predominant population is not of the Tfh-lineage. IL-10 deficient mice, which have increased IFN-γ and T-bet expression, demonstrated expansion of both IFN-γ⁺IL-21⁺CXCR5⁺ cells and IFN-γ⁺ GC Tfh cells, suggesting a Th1 lineage for the former. In the memory phase, all Ifng⁺ T cells produced IL-21, but only a small percentage of highly proliferative Ifng⁺ T cells maintained a T-bet^hi phenotype. In chronic malaria infection, serum IFN-γ correlates with increased protection, and our observation suggests Ifng⁺ T cells are maintained by cellular division. In summary, we found that Ifng⁺ T cells are not strictly Tfh derived during malaria infection. T cells provide the host with a survival advantage when facing this well-equipped pathogen, therefore, understanding the lineage of pivotal T cell players will aid in the rational design of an effective malaria vaccine.

Reversible Reprogramming of Circulating Memory T Follicular Helper Cell Function during Chronic HIV Infection

Despite the overwhelming benefits of antiretroviral therapy (ART) in curtailing viral load in HIV-infected individuals, ART does not fully restore cellular and humoral immunity. HIV-infected individuals under ART show reduced responses to vaccination and infections and are unable to mount an effective antiviral immune response upon ART cessation. Many factors contribute to these defects, including persistent inflammation, especially in lymphoid tissues, where T follicular helper (Tfh) cells instruct and help B cells launch an effective humoral immune response. In this study we investigated the phenotype and function of circulating memory Tfh cells as a surrogate of Tfh cells in lymph nodes and found significant impairment of this cell population in chronically HIV-infected individuals, leading to reduced B cell responses. We further show that these aberrant memory Tfh cells exhibit an IL-2-responsive gene signature and are more polarized toward a Th1 phenotype. Treatment of functional memory Tfh cells with IL-2 was able to recapitulate the detrimental reprogramming. Importantly, this defect was reversible, as interfering with the IL-2 signaling pathway helped reverse the abnormal differentiation and improved Ab responses. Thus, reversible reprogramming of memory Tfh cells in HIV-infected individuals could be used to enhance Ab responses. Altered microenvironmental conditions in lymphoid tissues leading to altered Tfh cell differentiation could provide one explanation for the poor responsiveness of HIV-infected individuals to new Ags. This explanation has important implications for the development of therapeutic interventions to enhance HIV- and vaccine-mediated Ab responses in patients under ART.

IL-2 and IL-15 regulate CD8+ memory T-cell differentiation but are dispensable for protective recall responses

The ability to mount effective secondary responses is a cardinal feature of memory CD8(+) T cells. An understanding of the factors that regulate the generation and recall capacities of memory T cells remains to be ascertained. Several cues indicate that two highly related cytokines, IL-2 and IL-15, share redundant functions in this process. To establish their combined roles in memory CD8(+) T-cell development, maintenance, and secondary responses, we compared the outcome of adoptively transferred IL2Rβ(+/-) or IL2Rβ(-/-) CD8(+) T cells after an acute viral infection in mice. Our results demonstrate that both IL-2 and IL-15 signals condition the differentiation of primary and secondary short-lived effector cells by altering the transcriptional network governing lineage choices. These two cytokines also regulate the homeostasis of the memory T-cell pool, with effector memory CD8(+) T cells being the most sensitive to these two interleukins. Noticeably, the inability to respond to both cytokines limits the proliferation and survival of primary and secondary effectors cells, whereas it does not preclude potent cytotoxic functions and viral control either initially or upon rechallenge. Globally, these results indicate that lack of IL-2 and IL-15 signaling modulates the CD8(+) T-cell differentiation program but does not impede adequate effector functions.

High affinity IgM(+) memory B cells are generated through a germinal center-dependent pathway

During a T cell-dependent immune response, B cells undergo clonal expansion and selection and the induction of isotype switching and somatic hypermutation (SHM). Although somatically mutated IgM(+) memory B cells have been reported, it has not been established whether they are really high affinity B cells. We tracked (4-hydroxy-3-nitrophenyl) acetyl hapten-specific GC B cells from normal immunized mice based on affinity of their B cell receptor (BCR) and performed BCR sequence analysis. SHM was evident by day 7 postimmunization and increased with time, such that high affinity IgM(+) as well as IgG(+) memory B cells continued to be generated up to day 42. In contrast, class-switch recombination (CSR) was almost completed by day 7 and then the ratio of IgG1(+)/IgM(+) GC B cells remained unchanged. Together these findings suggest that IgM(+) B cells undergo SHM in the GC to generate high affinity IgM(+) memory cells and that this process continues even after CSR is accomplished.

Trans-presentation of IL-15 modulates STAT5 activation and Bcl-6 expression in TH1 cells

During infection, naïve CD4⁺ T helper cells differentiate into specialized effector subsets based upon environmental signals propagated by the cytokine milieu. Recently, this paradigm has been complicated by the demonstration that alterations in the cytokine environment can result in varying degrees of plasticity between effector T helper cell populations. Therefore, elucidation of the mechanisms by which cytokines regulate T helper cell differentiation decisions is increasingly important. The gamma common cytokine IL-15 is currently undergoing clinical trials for the treatment of malignancies, due to its well-established role in the regulation of natural killer and CD8⁺ T cell immune responses. However, the effect of IL-15 signaling on CD4⁺ T cell activity is incompletely understood. One mechanism by which IL-15 activity is conferred is through trans-presentation via the IL-15 receptor alpha subunit. Here, we demonstrate that differentiated T_H1 cells are responsive to trans-presented IL-15. Importantly, while trans-presentation of IL-15 results in STAT5 activation and maintenance of the T_H1 gene program, IL-15 treatment alone allows for increased Bcl-6 expression and the upregulation of a T_FH-like profile. Collectively, these findings describe a novel role for IL-15 in the modulation of CD4⁺ T cell responses and provide valuable insight for the use of IL-15 in immunotherapeutic approaches.

T Helper Lymphocyte Subsets and Plasticity in Autoimmunity and Cancer: An Overview

In response to cytokine signalling and other factors, CD4-positive T lymphocytes differentiate into distinct populations that are characterized by the production of certain cytokines and are controlled by different master transcription factors. The spectrum of such populations, which was initially limited to Th1 and Th2 subsets, is currently broadened to include Th17 and Treg subsets, as well as a number of less studied subtypes, such as Tfh, Th9, and Th22. Although these subsets appear to be relatively stable, certain plasticity exists that allows for transition between the subsets and formation of hybrid transition forms. This provides the immune system flexibility needed for adequate response to pathogens but, at the same time, can play a role in the pathogenic processes in cases of deregulation. In this review, we will discuss the properties of T lymphocyte subsets and their plasticity, as well as its implications for cancer and autoimmune diseases.

Bcl6 middle domain repressor function is required for T follicular helper cell differentiation and utilizes the corepressor MTA3

T follicular helper (Tfh) cells are essential providers of help to B cells. The transcription factor B-cell CLL/lymphoma 6 (Bcl6) is a lineage-defining regulator of Tfh cells and germinal center B cells. In B cells, Bcl6 has the potential to recruit distinct transcriptional corepressors through its BTB domain or its poorly characterized middle domain (also known as RDII), but in Tfh cells the roles of the Bcl6 middle domain have yet to be clarified. Mimicked acetylation of the Bcl6 middle domain (K379Q) in CD4 T cells results in significant reductions in Tfh differentiation in vivo. Blimp1 (Prdm1) is a potent inhibitor of Tfh cell differentiation. Although Bcl6 K379Q still bound to the Prdm1 cis-regulatory elements in Tfh cells, Prdm1 expression was derepressed. This was a result of the failure of Bcl6 K379Q to recruit metastasis-associated protein 3 (MTA3). The loss of Bcl6 function in Bcl6 K379Q-expressing CD4 T cells could be partially rescued by abrogating Prdm1 expression. In addition to Prdm1, we found that Bcl6 recruits MTA3 to multiple genes involved in Tfh cell biology, including genes important for cell migration, cell survival, and alternative differentiation pathways. Thus, Bcl6 middle domain mediated repression is a major mechanism of action by which Bcl6 controls CD4 T-cell fate and function.

Targeting Transcriptional Regulators of CD8+ T Cell Dysfunction to Boost Anti-Tumor Immunity

Transcription is a dynamic process influenced by the cellular environment: healthy, transformed, and otherwise. Genome-wide mRNA expression profiles reflect the collective impact of pathways modulating cell function under different conditions. In this review we focus on the transcriptional pathways that control tumor infiltrating CD8+ T cell (TIL) function. Simultaneous restraint of overlapping inhibitory pathways may confer TIL resistance to multiple mechanisms of suppression traditionally referred to as exhaustion, tolerance, or anergy. Although decades of work have laid a solid foundation of altered transcriptional networks underlying various subsets of hypofunctional or “dysfunctional” CD8+ T cells, an understanding of the relevance in TIL has just begun. With recent technological advances, it is now feasible to further elucidate and utilize these pathways in immunotherapy platforms that seek to increase TIL function.

Predictive Value of Cytokines and Immune Activation Biomarkers in AIDS-Related Non-Hodgkin Lymphoma Treated with Rituximab plus Infusional EPOCH (AMC-034 trial)

PURPOSE

The aims of this study were to determine whether pretreatment plasma levels of cytokines and immune activation-associated molecules changed following treatment for AIDS-NHL with rituximab plus infusional EPOCH, and to determine whether pretreatment levels of these molecules were associated with response to treatment and/or survival.

EXPERIMENTAL DESIGN

We quantified plasma levels of B-cell activation-associated molecules (sCD27, sCD30, and sCD23) and cytokines (IL6, IL10, and CXCL13) before and after the initiation of treatment in persons with AIDS-NHL (n = 69) in the AIDS Malignancies Consortium (AMC) 034 study, which evaluated treatment of AIDS-NHL with EPOCH chemotherapy and rituximab.

RESULTS

Treatment resulted in decreased plasma levels of some of these molecules (CXCL13, sCD27, and sCD30), with decreased levels persisting for one year following the completion of treatment. Lower levels of CXCL13 before treatment were associated with complete responses following lymphoma therapy. Elevated levels of IL6 pretreatment were associated with decreased overall survival, whereas higher IL10 levels were associated with shorter progression-free survival (PFS), in multivariate analyses. Furthermore, patients with CXCL13 or IL6 levels higher than the median levels for the NHL group, as well as those who had detectable IL10, had lower overall survival and PFS, in Kaplan-Meier analyses.

CONCLUSIONS

These results indicate that CXCL13, IL6, and IL10 have significant potential as prognostic biomarkers for AIDS-NHL.

MiR-346 regulates CD4⁺CXCR5⁺ T cells in the pathogenesis of Graves' disease

Follicular helper T (Tfh) cells are increasingly recognized as participants in various autoimmune diseases, including Graves' disease. Although many transcription factors and cytokines are known to regulate Tfh cells, the role of noncoding RNA in Tfh cells development and function is poorly understood. Twenty-three patients with GD, eleven patients with remitting GD, and twenty-four healthy controls were enrolled in the current study. The interaction of miRNA and target gene was predicted through software analysis and then validated by luciferase assay and Western blot. The levels of miR-346 in circulating CD4(+) T cells and plasma were measured by qRT-PCR. The correlation of miR-346 levels with the percentages of CD4(+)CXCR5(+)T cells and autoantibody levels were also analyzed. Up-regulation of Bcl-6 and down-regulation of miR-346 in GD patients were observed, and miR-346 could inhibit Bcl-6 at both transcriptional and translational levels. Overexpression of miR-346 led to attenuating CD4(+)CXCR5(+) T cells. The abnormal expression of miR-346 restored in GD patients after treatment. A negative correlation between levels of miR-346 and percentages of CD4(+)CXCR5(+) T cells was confirmed in GD patients. Additionally, negative correlations between the levels of miR-346 in circulating CD4(+) T cells and serum concentrations of TR-Ab, TG-Ab, and TPO-Ab were also revealed in GD patients. MiR-346 regulates CD4(+)CXCR5(+) T cells by targeting Bcl-6, a positive regulator of Tfh cells, and might play an important role in the pathogenesis of Graves' disease.

An Inhibitory Role for the Transcription Factor Stat3 in Controlling IL-4 and Bcl6 Expression in Follicular Helper T Cells

The transcription factor Bcl6 is required for development of follicular helper T (TFH) cells. Cytokines that activate Stat3 promote Bcl6 expression and TFH cell differentiation. Previous studies with an acute virus infection model showed that TFH cell differentiation was decreased but not blocked in the absence of Stat3. In this study, we further analyzed the role of Stat3 in TFH cells. In Peyer's patches, we found that compared with wild-type, Stat3-deficient TFH cells developed at a 25% lower rate and expressed increased IFN-γ and IL-4. Whereas Peyer's patch germinal center B cells developed at normal numbers with Stat3-deficient TFH cells, IgG1 class switching was greatly increased. Following immunization with sheep RBCs, splenic Stat3-deficient TFH cells developed at a slower rate than in control mice, and splenic germinal center B cells were markedly decreased. Stat3-deficient TFH cells developed poorly in a competitive bone marrow chimera environment. Under all conditions tested, Stat3-deficient TFH cells overexpressed both IL-4 and Bcl6, a pattern specific for the TFH cell population. Finally, we found in vitro that repression of IL-4 expression in CD4 T cells by Bcl6 required Stat3 function. Our data indicate that Stat3 can repress the expression of Bcl6 and IL-4 in TFH cells, and that Stat3 regulates the ability of Bcl6 to repress target genes. Overall, we conclude that Stat3 is required to fine-tune the expression of multiple key genes in TFH cells, and that the specific immune environment determines the function of Stat3 in TFH cells.

Blimp1/Prdm1 Functions in Opposition to Irf1 to Maintain Neonatal Tolerance during Postnatal Intestinal Maturation

The neonatal intestine is a very complex and dynamic organ that must rapidly adapt and remodel in response to a barrage of environmental stimuli during the first few postnatal weeks. Recent studies demonstrate that the zinc finger transcriptional repressor Blimp1/Prdm1 plays an essential role governing postnatal reprogramming of intestinal enterocytes during this period. Functional loss results in global changes in gene expression patterns, particularly in genes associated with metabolic function. Here we engineered a knock-in allele expressing an eGFP-tagged fusion protein under control of the endogenous regulatory elements and performed genome wide ChIP-seq analysis to identify direct Blimp1 targets and further elucidate the function of Blimp1 in intestinal development. Comparison with published human and mouse datasets revealed a highly conserved core set of genes including interferon-inducible promoters. Here we show that the interferon-inducible transcriptional activator Irf1 is constitutively expressed throughout fetal and postnatal intestinal epithelium development. ChIP-seq demonstrates closely overlapping Blimp1 and Irf1 peaks at key components of the MHC class I pathway in fetal enterocytes. The onset of MHC class I expression coincides with down-regulated Blimp1 expression during the suckling to weaning transition. Collectively, these experiments strongly suggest that in addition to regulating the enterocyte metabolic switch, Blimp1 functions as a gatekeeper in opposition to Irf1 to prevent premature activation of the MHC class I pathway in villus epithelium to maintain tolerance in the neonatal intestine.

The transcriptional repressor Blimp1/Prdm1 plays a pivotal role in the metabolic switch that occurs in the small intestine during the suckling to weaning transition. Notably, expression profiling of perinatal Blimp1-deficient small intestine revealed premature activation of metabolic genes normally restricted to post-weaning enterocytes. To further elucidate the function of Blimp1 in intestinal development, we engineered a novel Blimp1-eGFP-fusion knock-in mouse strain to perform ChIP-seq analysis. In addition to identifying which metabolic genes are direct Blimp1 targets, ChIP-seq analysis revealed a highly conserved Blimp1/Irf-1 overlapping sites that function to control MHC class I antigen processing during acquisition of neonatal tolerance in the first weeks after birth during early colonization of the intestinal tract by commensal microorganisms. Moreover, immunohistochemical analysis of human fetal intestine suggests that a BLIMP1/IRF-1 axis may also function in human intestinal epithelium development.

TCR-Signaling Events in Cellular Metabolism and Specialization

Engaging the T cell receptor (TCR) with peptide:MHC complexes initiates a cascade of signaling events that activates T cells in an antigen-specific manner. It is now clear that multiple inputs, including the strength of TCR signaling, co-stimulation, and the cytokine environment, impact T cell specialization decisions in the context of specific pathogenic encounters. Additionally, it is now appreciated that these same stimuli direct cellular metabolism programs. In this review, we will discuss how TCR-signaling events coordinate cellular metabolism and specialization gene programs in T cells.

Pathogenic Transdifferentiation of Th17 Cells Contribute to Perpetuation of Rheumatoid Arthritis during Anti-TNF Treatment

T-helper cells producing interleukin (IL)-17A and IL-17F cytokines (Th17 cells) are considered the source of autoimmunity in rheumatoid arthritis (RA). In this study, we characterized specific pathogenic features of Th17 cells in RA. By using nano-string technology, we analyzed transcription of 419 genes in the peripheral blood CCR6(+)CXCR3(-) CD4(+) cells of 14 RA patients and 6 healthy controls and identified 109 genes discriminating Th17 cells of RA patients from the controls. Th17 cells of RA patients had an aggressive pathogenic profile and in addition to signature cytokines IL-17, IL-23 and IL-21, and transcriptional regulators RAR-related orphan receptor gamma of T cells (RORγt) and Janus kinase 2 (JAK2), they produced high levels of IL-23R, C-C chemokine ligand type 20 (CCL20), granulocyte-monocyte colony-stimulating factor (GM-CSF ) and transcription factor Tbet required for synovial homing. We showed that Th17 cells are enriched with Helios-producing Foxp3- and IL2RA-deficient cells, indicating altered regulatory profile. The follicular T-helper (Tfh) cells presented a functional profile of adaptor molecules, transcriptional regulator Bcl-6 and B-cell activating cytokines IL-21, IL-31 and leukemia inhibitory factor (LIF ). We observed that anti-tumor necrosis factor (TNF) treatment had a limited effect on the transcription signature of Th17 cells. Patients in remission retained the machinery of receptors (IL-23R and IL-1R1), proinflammatory cytokines (IL-17F, IL-23, IL-21 and TNF ) and adaptor molecules (C-X-C chemokine receptor 5 [CXCR5] and cytotoxic T-lymphocyte-associated protein 4 [CTLA-4]), essential for efficient transdifferentiation and accumulation of Th17 cells. This study convincingly shows that the peripheral blood CCR6(+)CXCR3(-) CD4(+) cells of RA patients harbor pathogenic subsets of Th17 and Tfh cells, which may transdifferentiate from Tregs and contribute to perpetuation of the disease.

Phenotypic switch of CD8(+) T cells reactivated under hypoxia toward IL-10 secreting, poorly proliferative effector cells

CD8(+) T cells controlling pathogens or tumors must function at sites where oxygen tension is frequently low, and never as high as under atmospheric culture conditions. However, T-cell function in vivo is generally analyzed indirectly, or is extrapolated from in vitro studies under nonphysiologic oxygen tensions. In this study, we delineate the role of physiologic and pathologic oxygen tension in vitro during reactivation and differentiation of tumor-specific CD8(+) T cells. Using CD8(+) T cells from pmel-1 mice, we observed that the generation of CTLs under 5% O2, which corresponds to physioxia in lymph nodes, gave rise to a higher effector signature than those generated under atmospheric oxygen fractions (21% O2). Hypoxia (1% O2) did not modify cytotoxicity, but decreasing O2 tensions during CTL and CD8(+) tumor-infiltrating lymphocyte reactivation dose-dependently decreased proliferation, induced secretion of the immunosuppressive cytokine IL-10, and upregulated the expression of CD137 (4-1BB) and CD25. Overall, our data indicate that oxygen tension is a key regulator of CD8(+) T-cell function and fate and suggest that IL-10 release may be an unanticipated component of CD8(+) T cell-mediated immune responses in most in vivo microenvironments.

Early Growth Response Genes 2 and 3 Regulate the Expression of Bcl6 and Differentiation of T Follicular Helper Cells

T follicular helper (Tfh) cells support differentiation of B cells to plasma cells and high affinity antibody production in germinal centers (GCs), and Tfh differentiation requires the function of B cell lymphoma 6 (BCL6). We have now discovered that early growth response gene 2 (EGR2) and EGR3 directly regulate the expression of Bcl6 in Tfh cells, which is required for their function in regulation of GC formation. In the absence of EGR2 and -3, the expression of BCL6 in Tfh cells is defective, leading to impaired differentiation of Tfh cells, resulting in a failure to form GCs following virus infection and defects in production of antiviral antibodies. Enforced expression of BCL6 in EGR2/3-deficient CD4 T cells partially restored Tfh differentiation and GC formation in response to virus infection. Our findings demonstrate a novel function of EGR2/3 that is important for Tfh cell development and Tfh cell-mediated B cell immune responses.

Early effector cells survive the contraction phase in malaria infection and generate both central and effector memory T cells

CD4 T cells orchestrate immunity against blood-stage malaria. However, a major challenge in designing vaccines to the disease is poor understanding of the requirements for the generation of protective memory T cells (Tmem) from responding effector T cells (Teff) in chronic parasite infection. In this study, we use a transgenic mouse model with T cells specific for the merozoite surface protein (MSP)-1 of Plasmodium chabaudi to show that activated T cells generate three distinct Teff subsets with progressive activation phenotypes. The earliest observed Teff subsets (CD127(-)CD62L(hi)CD27(+)) are less divided than CD62L(lo) Teff and express memory genes. Intermediate (CD62L(lo)CD27(+)) effector subsets include the most multicytokine-producing T cells, whereas fully activated (CD62L(lo)CD27(-)) late effector cells have a terminal Teff phenotype (PD-1(+), Fas(hi), AnnexinV(+)). We show that although IL-2 promotes expansion, it actually slows terminal effector differentiation. Using adoptive transfer, we show that only early Teff survive the contraction phase and generate the terminal late Teff subsets, whereas in uninfected recipients, they become both central and effector Tmem. Furthermore, we show that progression toward full Teff activation is promoted by increased duration of infection, which in the long-term promotes Tem differentiation. Therefore, we have defined markers of progressive activation of CD4 Teff at the peak of malaria infection, including a subset that survives the contraction phase to make Tmem, and show that Ag and cytokine levels during CD4 T cell expansion influence the proportion of activated cells that can survive contraction and generate memory in malaria infection.

Characterization of CD8+ T cell differentiation following SIVΔnef vaccination by transcription factor expression profiling

The onset of protective immunity against pathogenic SIV challenge in SIVΔnef-vaccinated macaques is delayed for 15-20 weeks, a process that is related to qualitative changes in CD8⁺ T cell responses induced by SIVΔnef. As a novel approach to characterize cell differentiation following vaccination, we used multi-target qPCR to measure transcription factor expression in naïve and memory subsets of CD8+⁺ T cells, and in SIV-specific CD8⁺ T cells obtained from SIVΔnef-vaccinated or wild type SIVmac239-infected macaques. Unsupervised clustering of expression profiles organized naïve and memory CD8⁺ T cells into groups concordant with cell surface phenotype. Transcription factor expression patterns in SIV-specific CD8⁺ T cells in SIVΔnef-vaccinated animals were distinct from those observed in purified CD8⁺ T cell subsets obtained from naïve animals, and were intermediate to expression profiles of purified central memory and effector memory T cells. Expression of transcription factors elicited by SIVΔnef vaccination also varied over time: cells obtained at later time points, temporally associated with greater protection, appeared more central-memory like than cells obtained at earlier time points, which appeared more effector memory-like. Expression of transcription factors associated with effector differentiation, such as ID2 and RUNX3, were decreased over time, while expression of transcription factors associated with quiescence or memory differentiation, such as TCF7, BCOR and EOMES, increased. CD8⁺ T cells specific for a more conserved epitope expressed higher levels of TBX21 and BATF, and appeared more effector-like than cells specific for an escaped epitope, consistent with continued activation by replicating vaccine virus. These data suggest transcription factor expression profiling is a novel method that can provide additional data complementary to the analysis of memory cell differentiation based on classical phenotypic markers. Additionally, these data support the hypothesis that ongoing stimulation by SIVΔnef promotes a distinct protective balance of CD8⁺ T cell differentiation and activation states.

The live attenuated vaccine SIVΔnef can induce robust CD8⁺ T cell- mediated protection against infection with pathogenic SIV in macaques. Thus, there is substantial interest in characterizing these immune responses to inform HIV vaccine design. Animals challenged at 15–20 weeks post vaccination exhibit robust protection, whereas animals challenged at 5 weeks post-vaccination manifest little protection. Since the frequency of SIV-specific T cells decreases from week 5 to week 20, it is likely that the quality of the response to challenge changes as virus-specific cells differentiate. We applied a novel approach of transcription factor expression profiling to characterize the differences in SIV-specific cell function and phenotype at more protected and less protected time points. Using unsupervised clustering methods informed by expression profiles assessed in purified CD8⁺ T cell subsets, we show that SIV-specific cells display expression profiles different than any purified CD8⁺ T cell subset, and intermediate to sorted effector memory and central memory subsets. SIV-specific cells overall appear more effector memory-like at week 5 post-vaccination, and more central memory-like at week 20 post-vaccination. Distinct profiles of CD8⁺ T cells specific for different SIV epitopes having different immune escape kinetics suggests maturation is regulated by ongoing low-level replication of vaccine virus.

Transcriptional regulatory networks for CD4 T cell differentiation

CD4(+) T cells play a central role in controlling the adaptive immune response by secreting cytokines to activate target cells. Naïve CD4(+) T cells differentiate into at least four subsets, Th1Th1 , Th2Th2 , Th17Th17 , and inducible regulatory T cellsregulatory T cells , each with unique functions for pathogen elimination. The differentiation of these subsets is induced in response to cytokine stimulation, which is translated into Stat activation, followed by induction of master regulator transcription factorstranscription factors . In addition to these factors, multiple other transcription factors, both subset specific and shared, are also involved in promoting subset differentiation. This review will focus on the network of transcription factors that control CD4(+) T cell differentiation.

Dynamics of B cells in germinal centres

Humoral immunity depends on the germinal centre (GC) reaction during which somatically mutated high-affinity memory B cells and plasma cells are generated. Recent studies have uncovered crucial cues that are required for the formation and the maintenance of GCs and for the selection of high-affinity antibody mutants. In addition, it is now clear that these events are promoted by the dynamic movements of cells within and between GCs. These findings have resolved the complexities of the GC reaction in greater detail than ever before. This Review focuses on these recent advances and discusses their implications for the establishment of humoral immunity.

A brief history of T cell help to B cells

In celebration of the 50th anniversary of the discovery of B cells, I take a look back at the history of T cell help to B cells, which was discovered 47 years ago. In addition, I summarize and categorize the distinct molecules that are expressed by CD4(+) T cells that constitute 'help' to B cells, and particularly the molecules expressed by T follicular helper (TFH) cells, which are the specialized providers of help to B cells.

CD4 T-cell memory generation and maintenance

Immunologic memory is the adaptive immune system's powerful ability to remember a previous antigen encounter and react with accelerated vigor upon antigen re-exposure. It provides durable protection against reinfection with pathogens and is the foundation for vaccine-induced immunity. Unlike the relatively restricted immunologic purview of memory B cells and CD8 T cells, the field of CD4 T-cell memory must account for multiple distinct lineages with diverse effector functions, the issue of lineage commitment and plasticity, and the variable distribution of memory cells within each lineage. Here, we discuss the evidence for lineage-specific CD4 T-cell memory and summarize the known factors contributing to memory-cell generation, plasticity, and long-term maintenance.

Blimp-1, an intrinsic factor that represses HIV-1 proviral transcription in memory CD4+ T cells

CD4(+) T cell subsets differentially support HIV-1 replication. For example, quiescent CD4(+) memory T cells are susceptible to HIV-1 infection but do not support robust HIV-1 transcription and have been implicated as the primary reservoir of latent HIV-1. T cell transcription factors that regulate maturation potentially limit HIV-1 transcription and mediate the establishment and maintenance of HIV-1 latency. We report that B lymphocyte-induced maturation protein-1 (Blimp-1), a critical regulator of B and T cell differentiation, is highly expressed in memory CD4(+) T cells compared with naive CD4(+) T cells and represses basal and Tat-mediated HIV-1 transcription. Blimp-1 binds an IFN-stimulated response element within HIV-1 provirus, and it is displaced following T cell activation. Reduction of Blimp-1 in infected primary T cells including CD4(+) memory T cells increases RNA polymerase II processivity, histone acetylation, and baseline HIV-1 transcription. Therefore, the transcriptional repressor, Blimp-1, is an intrinsic factor that predisposes CD4(+) memory T cells to latent HIV-1 infection.

CD4 T Cells Mediate Both Positive and Negative Regulation of the Immune Response to HIV Infection: Complex Role of T Follicular Helper Cells and Regulatory T Cells in Pathogenesis

HIV-1 infection results in chronic activation of cells in lymphoid tissue, including T cells, B-cells, and myeloid lineage cells. The resulting characteristic hyperplasia is an amalgam of proliferating host immune cells in the adaptive response, increased concentrations of innate response mediators due to viral and bacterial products, and homeostatic responses to inflammation. While it is generally thought that CD4 T cells are greatly depleted, in fact, two types of CD4 T cells appear to be increased, namely, regulatory T cells (Tregs) and T follicular helper cells (Tfh). These cells have opposing roles, but may both be important in the pathogenic process. Whether Tregs are failing in their role to limit lymphocyte activation is unclear, but there is no doubt now that Tfh are associated with B-cell hyperplasia and increased germinal center activity. Antiretroviral therapy may reduce the lymphocyte activation, but not completely, and therefore, there is a need for interventions that selectively enhance normal CD4 function without exacerbating Tfh, B-cell, or Treg dysfunction.

Involvement of MicroRNA in T-Cell Differentiation and Malignancy

MicroRNAs are 19-22 nucleotide RNAs involved in such important processes as development, proliferation, differentiation and apoptosis. Different miRNAs are uniquely expressed in lymphoid T cells, and play a role indevelopment and differentiation of various subtypes by targeting their target genes. Recent studies have shown that aberrant miRNA expression may be involved in T cell leukemogenesis and lymphogenesis, and may function as tumor suppressor (such as miR-451, miR-31, miR-150, and miR-29a) or oncogene (e.g. miR-222, miR-223, miR-17-92, miR-155). MiRNAs can be used as new biomarkers for prognosis and diagnosis or as an index of disease severity in T-cell leukemia and lymphoma. This article presents a review of studies in recent years on the role of miRNAs in T-cell development and their aberrant expression in pathogenesis of T-cell leukemia and lymphoma. Characterizing miRNAs can help recognize their role as new important molecules with prognostic and therapeutic applications.

Transcriptional Control of NK Cells

Natural killer (NK) cells are innate lymphocytes that survey the environment and protect the host from infected and cancerous cells. As their name implies, NK cells represent an early line of defense during pathogen invasion by directly killing infected cells and secreting inflammatory cytokines. Although the function of NK cells was first described more than four decades ago, the development of this cytotoxic lineage is not well understood. In recent years, we have begun to identify specific transcription factors that control each stage of development and maturation, from ontogeny of the NK cell progenitor to the effector functions of activated NK cells in peripheral organs. This chapter highlights the transcription factors that are unique to NK cells, or shared between NK cells and other hematopoietic cell lineages, but govern the biology of this cytolytic lymphocyte.

The specialized proresolving mediator 17-HDHA enhances the antibody-mediated immune response against influenza virus: a new class of adjuvant?

Influenza viruses remain a critical global health concern. More efficacious vaccines are needed to protect against influenza virus, yet few adjuvants are approved for routine use. Specialized proresolving mediators (SPMs) are powerful endogenous bioactive regulators of inflammation, with great clinical translational properties. In this study, we investigated the ability of the SPM 17-HDHA to enhance the adaptive immune response using an OVA immunization model and a preclinical influenza vaccination mouse model. Our findings revealed that mice immunized with OVA plus 17-HDHA or with H1N1-derived HA protein plus 17-HDHA increased Ag-specific Ab titers. 17-HDHA increased the number of Ab-secreting cells in vitro and the number of HA-specific Ab-secreting cells present in the bone marrow. Importantly, the 17-HDHA-mediated increased Ab production was more protective against live pH1N1 influenza infection in mice. To our knowledge, this is the first report on the biological effects of ω-3-derived SPMs on the humoral immune response. These findings illustrate a previously unknown biological link between proresolution signals and the adaptive immune system. Furthermore, this work has important implications for the understanding of B cell biology, as well as the development of new potential vaccine adjuvants.

A p85α-osteopontin axis couples the receptor ICOS to sustained Bcl-6 expression by follicular helper and regulatory T cells

Follicular helper T cells (TFH cells) and follicular regulatory T cells (TFR cells) regulate the quantity and quality of humoral immunity. Although both cell types express the costimulatory receptor ICOS and require the transcription factor Bcl-6 for their differentiation, the ICOS-dependent pathways that coordinate their responses are not well understood. Here we report that activation of ICOS in CD4(+) T cells promoted interaction of the p85α regulatory subunit of the signaling kinase PI(3)K and intracellular osteopontin (OPN-i), followed by translocation of OPN-i to the nucleus, its interaction with Bcl-6 and protection of Bcl-6 from ubiquitin-dependent proteasome degradation. Post-translational protection of Bcl-6 by OPN-i was essential for sustained responses of TFH cells and TFR cells and regulation of the germinal center B cell response to antigen. Thus, the p85α-OPN-i axis represents a molecular bridge that couples activation of ICOS to Bcl-6-dependent functional differentiation of TFH cells and TFR cells; this suggests new therapeutic avenues to manipulate the responses of these cells.

A large candidate-gene association study suggests genetic variants at IRF5 and PRDM1 to be associated with aggressive periodontitis

AIM

Epidemiological and clinical studies indicated a relationship of periodontitis with rheumatoid arthritis (RA). We aimed to identify shared genetic susceptibility loci of RA and periodontitis.

MATERIALS AND METHODS

Forty-seven risk genes of genome-wide significance of RA and SLE were genotyped in a German case-control sample of aggressive periodontitis (AgP), using Immunochip genotyping arrays (Illumina, 600 cases, 1440 controls) and Affymetrix 500 K Genotyping Arrays (280 cases and 983 controls). Significant associations were replicated in 168 Dutch AgP cases and 679 controls and adjusted for the confounders smoking and sex.

RESULTS

Variants at IRF5 and PRDM1 showed association with AgP. Upon covariate adjustment for smoking and sex, the most strongly associated variant at IRF5 was the rare variant rs62481981 (ppooled  = 0.0012, odds ratio [OR] = 3.1, 95% confidence interval [95% CI] = 1.6-6.1; 801 cases, 1476 controls).Within PRDM1 it was rs6923419 (ppooled  = 0.004, OR = 0.7, 95% CI = 0.6-0.9; 833 cases, 1440 controls). The associations lost significance after correction for multiple testing in the replication. Both genes are implicated in beta-interferon signalling and are also genome-wide associated with SLE and inflammatory bowel disease.

CONCLUSION

The study gives no definite evidence for a pathogenic genetic link of periodontitis and RA but suggests IRF5 and PRDM1 as shared susceptibility factors.

FOXO1 repression contributes to block of plasma cell differentiation in classical Hodgkin lymphoma

FOXO1 directly activates PRDM1α, the master regulator of PC differentiation, and it enriches a PC signature in cHL cell lines. PRDM1α is a tumor suppressor in cHL.

Histone deacetylase inhibitors upregulate B cell microRNAs that silence AID and Blimp-1 expression for epigenetic modulation of antibody and autoantibody responses

Class-switch DNA recombination (CSR) and somatic hypermutation (SHM), which require activation-induced cytidine deaminase (AID), and plasma cell differentiation, which requires B lymphocyte-induced maturation protein-1 (Blimp-1), are critical for the generation of class-switched and hypermutated (mature) Ab and autoantibody responses. We show that histone deacetylase inhibitors valproic acid and butyrate dampened AICDA/Aicda (AID) and PRDM1/Prdm1 (Blimp-1) mRNAs by upregulating miR-155, miR-181b, and miR-361 to silence AICDA/Aicda, and miR-23b, miR-30a, and miR-125b to silence PRDM1/Prdm1, in human and mouse B cells. This led to downregulation of AID, Blimp-1, and X-box binding protein 1, thereby inhibiting CSR, SHM, and plasma cell differentiation without altering B cell viability or proliferation. The selectivity of histone deacetylase inhibitor-mediated silencing of AICDA/Aicda and PRDM1/Prdm1 was emphasized by unchanged expression of HoxC4 and Irf4 (important inducers/modulators of AICDA/Aicda), Rev1 and Ung (central elements for CSR/SHM), and Bcl6, Bach2, or Pax5 (repressors of PRDM1/Prdm1 expression), as well as unchanged expression of miR-19a/b, miR-20a, and miR-25, which are not known to regulate AICDA/Aicda or PRDM1/Prdm1. Through these B cell-intrinsic epigenetic mechanisms, valproic acid blunted class-switched and hypermutated T-dependent and T-independent Ab responses in C57BL/6 mice. In addition, it decreased class-switched and hypermutated autoantibodies, ameliorated disease, and extended survival in lupus MRL/Fas(lpr/lpr) mice. Our findings outline epigenetic mechanisms that modulate expression of an enzyme (AID) and transcription factors (Blimp-1 and X-box binding protein 1) that are critical to the B cell differentiation processes that underpin Ab and autoantibody responses. They also provide therapeutic proof-of-principle in autoantibody-mediated autoimmunity.

Follicular helper T lymphocytes in health and disease

A correct antibody response requires the participation of both B and T lymphocytes and antigen presenting cells. In this review we address the role of follicular helper T lymphocytes (T_FH) in this reaction. We shall focus on the regulation of their development and function in health and disease. T_FH can be characterized on the basis of their phenotype and the pattern of secretion of cytokines. This fact is useful to study their participation in the generation of antibody deficiency in primary immunodeficiency diseases such as common variable immunodeficiency, X-linked hyper IgM syndrome or X-linked lymphoproliferative disease. Increased numbers of T_FH have been demonstrated in several autoimmune diseases and are thought to play a role in the development of autoantibodies. In chronic viral infections caused by the human immunodeficiency virus, hepatitis B or C virus, increased circulating T_FH have been observed, but their role in the protective immune response to these agents is under discussion. Likewise, an important role of T_FH in the control of some experimental protozoan infections has been proposed, and it will be important to assess their relevance in order to design effective vaccination strategies.

Pellino 1 promotes lymphomagenesis by deregulating BCL6 polyubiquitination

The signal-responsive E3 ubiquitin ligase pellino 1 (PELI1) regulates TLR and T cell receptor (TCR) signaling and contributes to the maintenance of autoimmunity; however, little is known about the consequence of mutations that result in upregulation of PELI1. Here, we developed transgenic mice that constitutively express human PELI1 and determined that these mice have a shorter lifespan due to tumor formation. Constitutive expression of PELI1 resulted in ligand-independent hyperactivation of B cells and facilitated the development of a wide range of lymphoid tumors, with prominent B cell infiltration observed across multiple organs. PELI1 directly interacted with the oncoprotein B cell chronic lymphocytic leukemia (BCL6) and induced lysine 63-mediated BCL6 polyubiquitination. In samples from patients with diffuse large B cell lymphomas (DLBCLs), PELI1 expression levels positively correlated with BCL6 expression, and PELI1 overexpression was closely associated with poor prognosis in DLBCLs. Together, these results suggest that increased PELI1 expression and subsequent induction of BCL6 promotes lymphomagenesis and that this pathway may be a potential target for therapeutic strategies to treat B cell lymphomas.

Bcl-6 directly represses the gene program of the glycolysis pathway

Despite the increasing knowledge of the molecular events that induce the glycolysis pathway in effector T cells, very little is known about the transcriptional mechanisms that dampen the glycolysis program in quiescent cell populations such as memory T cells. Here we found that the transcription factor Bcl-6 directly repressed genes encoding molecules involved in the glycolysis pathway, including Slc2a1, Slc2a3, Pkm and Hk2, in type 1 helper T cells (TH1 cells) exposed to low concentrations of interleukin 2 (IL-2). Thus, Bcl-6 had a role opposing the IL-2-sensitive glycolytic transcriptional program that the transcription factors c-Myc and HIF-1α promote in effector T cells. Additionally, the TH1 lineage-specifying factor T-bet functionally antagonized the Bcl-6-dependent repression of genes encoding molecules in the glycolysis pathway, which links the molecular balance of these two factors to regulation of the metabolic gene program.