Commensal microbe-derived butyrate enhances T follicular helper cell function to boost mucosal vaccine efficacy.

The generation of Immunglobulin (Ig) E and high-affinity IgG1 by B cells is a hallmark of allergic inflammation. These hallmarks are heavily reliant on interactions with T follicular helper (Tfh) cells. A critical cytokine provided by Tfh cells to the germinal center B cells is Interleukin-4 (IL-4). The mechanisms controlling IL-4 production by Tfh cells remain unknown. Given that Notch signaling is required for the differentiation of Tfh cells and it is known to influence cytokine production in T cells, we hypothesized that Notch also plays an important role in regulating the function of Tfh cells. Here, we use intestinal helminth infection to characterize whether persistent Notch signaling is required to maintain Tfh cell fate and function during allergic immunity. Genetic deletion of Notch receptors in infected mice results in reduced IL-4 production by Tfh and Th2 cells. Conversely, over-expression of Notch signaling leads to increased IL-4 production by Tfh cells. However, increased Notch signaling also appears to alter Tfh cell fate and phenotype. In support, chemical inhibition of Notch signaling after Tfh differentiation results in decreased expression of the Tfh chemokine receptor, CXCR5 among IL-4 producing T cells in the lymph node. These findings suggest that Notch signaling is not only important for Tfh differentiation, but that strength of Notch signaling is important for regulating Tfh cell fate, function, and maintenance.

The follicular helper T (Tfh) cells help is critical for activation of B cells, antibody class switching, and germinal center (GC) formation. The Tfh cells are characterized by the expression of CXC chemokine receptor 5 (CXCR5), ICOS, programed death 1 (PD-1), B cell lymphoma 6 (BCL-6), and IL-21. They are involved in clearing infections and are adversely linked with autoimmune diseases and also have a role in viral replication as well as clearance. On the one hand, Tfh cells are generated from naive CD4+ T cells with sequential steps involving cytokine signaling (IL-21, IL-6, IL-12, activin A), migration, and positioning in the GC by CXCR5, surface receptors (ICOS/ICOSL, signaling lymphocyte activation molecule-associated protein/signaling lymphocyte activation molecule) as well as transcription factor (BCL-6, c-Maf, and signal transducer and activator of transcription 3) signaling and repressor miR155. On the other hand, Tfh generation is negatively regulated at specific steps of Tfh generation by specific cytokine (IL-2, IL-7), surface receptor (PD-1, CTLA-4), transcription factors B lymphocyte maturation protein 1, signal transducer and activator of transcription 5, T-bet, KLF-2 signaling, and repressor miR 146a. Interestingly, miR-17–92 and FOXO1 act as a positive as well as a negative regulator of Tfh differentiation depending on the time of expression and disease specificity. Tfh cells are also generated from the conversion of other effector T cells as exemplified by Th1 cells converting into Tfh during viral infection. The mechanistic details of effector T cells conversion into Tfh are yet to be clear. To manipulate Tfh cells for therapeutic implication and or for effective vaccination strategies, it is important to know positive and negative regulators of Tfh generation. Hence, in this review, we have highlighted and interlinked molecular signaling from cytokines, surface receptors, transcription factors, ubiquitin ligase, and microRNA as positive and negative regulators for Tfh differentiation.

T follicular helper (Tfh) cells are a specialized subset of CD4+ T lymphocytes that are essential for the development of long-lasting humoral immunity. Tfh cells facilitate B lymphocyte maturation, promote germinal center formation, and drive high-affinity antibody production. Our current knowledge of Tfh interactions with the humoral immune system effectors suggests that they have a critical role in supporting the immune response against viral infections. This review discusses the mechanisms through which Tfh cells influence anti-viral immunity, highlighting their interactions with B cells and their impact on antibody quality and quantity. We explore the role of Tfh cells in viral infections and examine how vaccine design can be improved to enhance Tfh cell responses. Innovative vaccine platforms, such as mRNA vaccines and self-assembling protein nanoplatforms (SAPNs), are promising strategies to enhance Tfh cell activation. Their integration and synergistic combination could further enhance immunity and Tfh responses (SAPN-RNA vaccines). In summary, we provide a comprehensive overview of the current insights into Tfh cells' role during viral infections, emphasizing their potential as strategic targets for innovative vaccine development.

FRI0369 Uc-Mscs Inhibit the Differentiation and Proliferation of T Follicular Helper Cell in Rheumatoid Arthritis

Recent work has identified a new subset of CD4+ T cells named as T follicular helper (Tfh) cells that are localized in germinal centers and critical in germinal-center formation. Tfh cell differentiation is regulated by IL-6 and IL-21, possibly via STAT3 factor, and Bcl6 is specifically expressed in Tfh cells and required for their lineage specification. In current study, we characterized the role of STAT5 in developmental regulation of Tfh cells. We found that a constitutively active form of STAT5 effectively inhibited Tfh differentiation by suppressing the expression of Tfh-associated factors CXCR5, c-Maf, Bcl6, Batf and IL-21, whereas STAT5 deficiency greatly enhanced Tfh differentiation. In addition, deletion of STAT5 in CD4+ T cells in vivo resulted in enhanced development of Tfh cells and germinal center B cells, and led to an impairment of B cell tolerance, suggesting that STAT5 signaling controls the humoral immunity. This knowledge may help us to find ways to treat antibody-mediated autoimmune diseases.

The main avenue for the development of an HIV-1 vaccine remains the induction of protective antibodies. A rationale approach is to target antigen to specific receptors on dendritic cells (DC) via fused monoclonal antibodies (mAb). In mouse and non-human primate models, targeting of skin Langerhans cells (LC) with anti-Langerin mAbs fused with HIV-1 Gag antigen drives antigen-specific humoral responses. The development of these immunization strategies in humans requires a better understanding of early immune events driven by human LC. We therefore produced anti-Langerin mAbs fused with the HIV-1 gp140z Envelope (αLC.Env). First, we show that primary skin human LC and in vitro differentiated LC induce differentiation and expansion of naïve CD4+ T cells into T follicular helper (Tfh) cells. Second, when human LC are pre-treated with αLC.Env, differentiated Tfh cells significantly promote the production of specific IgG by B cells. Strikingly, HIV-Env-specific Ig are secreted by HIV-specific memory B cells. Consistently, we found that receptors and cytokines involved in Tfh differentiation and B cell functions are upregulated by LC during their maturation and after targeting Langerin. Finally, we show that subcutaneous immunization of mice by αLC.Env induces germinal center (GC) reaction in draining lymph nodes with higher numbers of Tfh cells, Env-specific B cells, as well as specific IgG serum levels compared to mice immunized with the non-targeting Env antigen. Altogether, we provide evidence that human LC properly targeted may be licensed to efficiently induce Tfh cell and B cell responses in GC.

Human and mouse studies performed over the last decade have established that follicular helper T (Tfh) cells are a CD4(+) helper subset specialized in the provision of help to B cells. Tfh differentiation is driven by expression of the transcriptional repressor B-cell lymphoma-6 (Bcl-6), which turns on a program that guides T cells close to B-cell areas where Tfh cells first provide help to B cells. Sustained Bcl-6 expression promotes the entry of Tfh cells into follicles and modulates their cytokine expression profile so they can support and select germinal center B cells that have acquired affinity-enhancing mutations in their immunoglobulin genes. Forkhead box 3 protein (Foxp3)(+) regulatory T cells and invariant natural killer T (NKT) cells can also co-opt the Bcl-6-dependent follicular differentiation pathway to migrate into B-cell follicles and regulate antibody responses. The resulting NKT follicular helper cells drive a distinctive type of T-dependent B-cell response to lipid-containing antigens, whereas FoxP3(+) follicular regulatory (Tfr) cells exert a suppressive function on germinal centers. Elucidating how Tfr cells are functionally and numerically regulated and the factors that control the balance between Tfh and Tfr cells is likely to be critical for improved understanding of the pathogenesis and progression of autoimmunity and lymphomas of germinal center origin, and generation of effective vaccines.

The main avenue for the development of an HIV-1 vaccine remains the induction of protective antibodies. A rationale approach is to target antigen to specific receptors on dendritic cells (DC) via fused monoclonal antibodies (mAb). In mouse and non-human primate models, targeting of skin Langerhans cells (LC) with anti-Langerin mAbs fused with HIV-1 Gag antigen drives antigen-specific humoral responses. The development of these immunization strategies in humans requires a better understanding of early immune events driven by human LC. We therefore produced anti-Langerin mAbs fused with the HIV-1 gp140z Envelope (αLC.Env). First, we show that primary skin human LC and in vitro differentiated LC induce differentiation and expansion of naïve CD4+ T cells into T follicular helper (Tfh) cells. Second, when human LC are pre-treated with αLC.Env, differentiated Tfh cells significantly promote the production of specific IgG by B cells. Strikingly, HIV-Env-specific Ig are secreted by HIV-specific memory B cells. Consistently, we found that receptors and cytokines involved in Tfh differentiation and B cell functions are upregulated by LC during their maturation and after targeting Langerin. Finally, we show that subcutaneous immunization of mice by αLC.Env induces germinal center (GC) reaction in draining lymph nodes with higher numbers of Tfh cells, Env-specific B cells, as well as specific IgG serum levels compared to mice immunized with the non-targeting Env antigen. Altogether, we provide evidence that human LC properly targeted may be licensed to efficiently induce Tfh cell and B cell responses in GC.

T follicular helper (Tfh) cells are specialized to provide help to B cells and to induce durable antibody response. Our knowledge on the biology of Tfh cells and their contribution to disease has significantly increased in the past decade. In particular, recent discoveries of functionally distinct subsets within circulating Tfh (cTfh) cells in human blood have provided clues to assess the ongoing Tfh responses in healthy subjects after vaccinations and in patients with autoimmune diseases. The immune pathways associated with Tfh cell differentiation in humans are also getting revealed. In this review, I will first summarize the subsets within human cTfh cells, and discuss their alterations in patients with autoimmune diseases. Then I will discuss the mechanisms associated with the aberrant Tfh responses in human autoimmune diseases.

Increasing evidence highlights a critical role of T follicular helper (Tfh) cells in autoimmune pathogenesis. This study aimed to identify inflammatory cytokines involved in driving Tfh cell responses in systemic lupus erythematosus (SLE). The circulating Tfh frequencies and interferon (IFN)-β levels were analyzed for correlations with disease activities in patients with SLE. Both lupus mice with IFN-β treatment and Ifnar1-/- mice with lupus induction were assessed for Tfh cell responses and disease progression. Sorting-purified naive CD4+T cells from Ifnar1-/- mice were adoptively transferred to lupus mice for monitoring Tfh cell differentiation in vivo. In culture, mouse CD4+T cells treated with IFN-β were examined for Tfh cell differentiation and intracellular signaling pathway. The underlying mechanism for IFN-β secretion by myeloid-derived suppressor cells (MDSCs) was investigated by co-immunoprecipitation and Western blotting. We found that increased Tfh cells with IFN-I-inducible gene signatures correlated with disease activities in patients with SLE. Consistently, IFN-β treatment markedly enhanced Tfh cell response and exacerbated disease progression in lupus mice. Moreover, mice with IFNAR1 deficiency exhibited attenuated lupus progression with significantly decreased Tfh response. Mechanistically, IFN-β activated the indoleamine 2,3-dioxygenase/kynurenine/aryl hydrocarbon receptor (IDO/Kyn/AhR)axis to promote Tfh cell differentiation. Notably, expanded MDSCs in lupus were found to produce high levels of IFN-β. Further studies showed that the autoantigen activated lymphocyte-derived DNA stimulated IFN-β production by MDSCs via the cyclic GMP-AMP synthase-stimulator of IFN genes (cGAS-STING)-dependent pathway. These results have demonstrated a novel function of IFN-β in promoting Tfh cell response during lupus progression, which may facilitate the identification of new therapeutic targets for the treatment of SLE.

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract infections in children under 1 year. RSV vaccines are currently unavailable, and children suffering from multiple reinfections by the same viral strain fail to develop protective responses. Although RSV-specific antibodies can be detected upon infection, these have limited neutralizing capacity. Follicular helper T (Tfh) cells are specialized in providing signals to B cells and help the production and affinity maturation of antibodies, mainly via interleukin (IL) 21 secretion. In this study, we evaluated whether RSV could inhibit Tfh responses. We observed that Tfh cells fail to upregulate IL-21 production upon RSV infection. In the lungs, RSV infection downregulated the expression of IL-21/interleukin-21 receptor (IL-21R) in Tfh cells and upregulated programmed death-ligand 1 (PD-L1) expression in dendritic cells (DCs) and B cells. PD-L1 blockade during infection recovered IL-21R expression in Tfh cells and increased the secretion of IL-21 in a DC-dependent manner. IL-21 treatment decreased RSV viral load and lung inflammation, inducing the formation of tertiary lymphoid organs in the lung. It also decreased regulatory follicular T cells, and increased Tfh cells, B cells, antibody avidity and neutralization capacity, leading to an overall improved anti-RSV humoral response in infected mice. Passive immunization with purified immunoglobulin G from IL-21-treated RSV-infected mice protected against RSV infection. Our results unveil a pathway by which RSV affects Tfh cells by increasing PD-L1 expression on antigen-presenting cells, highlighting the importance of an IL-21-PD-L1 axis for the generation of protective responses to RSV infection.

A poor immune response is a hallmark of aging. Older individuals are more susceptible to infections and respond poorly to new immunization. This is caused, at least in part, by a defective antibody response. We have shown that age-associated defects impair CD4 T cell functions. Since an optimal antibody response requires good CD4 cognate help through T follicular helper (Tfh) cells, we aimed to determine whether the impaired cognate help resulted from defects in the generation and/or functions of Tfh cells in aged mice. The work presented herein shows that the generation of Tfh cells in response to influenza immunization is delayed, reduced and shortened in aged mice compared to young mice. Also fewer Tfh cells are generated in aged mice than in young mice following influenza infection. The Tfh cells generated in aged mice, however, express similar levels of IL-21, BCL-6, CXCR5 and IL-4 mRNA than Tfh cells from young mice. These data suggest that the generation rather than the functions of Tfh cells is impaired in aged mice. The addition of poly(I:C) as an adjuvant to the influenza vaccine increases Tfh generation and antibody production in young and aged mice. We are investigating the mechanisms by which TLR ligands improve the Tfh response.

Genetic analysis of the potential role of IgA and IgE responses against Haemonchus contortus in parasite resistance of Creole goats

Background: T follicular helper CD4+ cells (Tfh) are essential for maintenance of systemic lupus erythematosus (SLE) as they help germinal center B cells generate high affinity auto-antibodies. The activation of STAT3 is critical for generation of Tfh cells as it promotes the transcription of BCL6 (the essential transcription factor for Tfh cell differentiation). It is recognized that activated, proliferating SLE CD4+ T cells, contain more iron than controls. Iron binds CDK1 to accentuate JAK1 phosphorylation and activation of STAT3 in proliferating cells. Whether increased iron content of SLE CD4+ T cells augments JAK1-STAT3 signaling and their differentiation into Tfh cells has not been investigated. Experiments: RNAseq and qPCR was used to compare iron regulatory pathways in purified Tfh cells from WT and SLE-prone mice. Labile iron (bio-active) content was measured in freshly isolated Tfh cells. The effect of iron chelator on in vitro Tfh differentiation and effector function was evaluated. Results: Compared to WT, SLE Tfh cells displayed significant increase in genes associated with iron uptake and transmembrane iron transport. Labile iron content and CDK1 gene expression were elevated in SLE Tfh cells. Iron chelation attenuated STAT3 activation, BCL6 expression and IL-21 production in in vitro generated Tfh cells. Conclusion: Our novel data identify an essential role of iron in Tfh cell differentiation and effector function. Increased iron and CDK1 may amplify JAK1-STAT3 signaling and potentiate Tfh cell differentiation. This can be blocked by restricting free iron availability. Understanding this aspect of Tfh cell biology in SLE may support strategies that control labile iron as potential adjunct therapy. Supported by grants from Vifor Pharma (P0213104, P0226952) to Yogesh Scindia NIH (R01AI135128) to Borna Mehrad NIH (R01AI128901) to Laurence Morel

The immunobiology of hepatocellular carcinoma in humans and mice: Basic concepts and therapeutic implications