Cholera toxin directly enhances IL-17A production from human CD4+ T cells

Robust microbe immune recognition in the intestinal mucosa

The mammalian mucosal immune system acts as a multitasking mediator between bodily function and a vast diversity of microbial colonists. Depending on host-microbial interaction type, mucosal immune responses have distinct functions. Immunity to pathogen infection functions to limit tissue damage, clear or contain primary infection, and prevent or lower the severity of a secondary infection by conferring specific long-term adaptive immunity. Responses to nonpathogenic commensal or mutualistic microbes instead function to tolerate continuous colonization. Mucosal innate immune and epithelial cells employ a limited repertoire of innate receptors to program the adaptive immune response accordingly. Pathogen versus nonpathogen immune discrimination appears to be very robust, as most individuals successfully maintain life-long mutualism with their nonpathogenic microbiota, while mounting immune defense to pathogenic microbe infection specifically. However, the process is imperfect, which can have immunopathological consequences, but may also be exploited medically. Normally innocuous intestinal commensals in some individuals may drive serious inflammatory autoimmunity, whereas harmless vaccines can be used to fool the immune system into mounting a protective anti-pathogen immune response. In this article, we review the current knowledge on mucosal intestinal bacterial immune recognition focusing on T_H17 responses and identify commonalities between intestinal pathobiont and vaccine-induced T_H17 responses.

Targeting Adenosine in Cancer Immunotherapy to Enhance T-Cell Function

T cells play a critical role in cancer control, but a range of potent immunosuppressive mechanisms can be upregulated in the tumor microenvironment (TME) to abrogate their activity. While various immunotherapies (IMTs) aiming at re-invigorating the T-cell-mediated anti-tumor response, such as immune checkpoint blockade (ICB), and the adoptive cell transfer (ACT) of natural or gene-engineered ex vivo expanded tumor-specific T cells, have led to unprecedented clinical responses, only a small proportion of cancer patients benefit from these treatments. Important research efforts are thus underway to identify biomarkers of response, as well as to develop personalized combinatorial approaches that can target other inhibitory mechanisms at play in the TME. In recent years, adenosinergic signaling has emerged as a powerful immuno-metabolic checkpoint in tumors. Like several other barriers in the TME, such as the PD-1/PDL-1 axis, CTLA-4, and indoleamine 2,3-dioxygenase (IDO-1), adenosine plays important physiologic roles, but has been co-opted by tumors to promote their growth and impair immunity. Several agents counteracting the adenosine axis have been developed, and pre-clinical studies have demonstrated important anti-tumor activity, alone and in combination with other IMTs including ICB and ACT. Here we review the regulation of adenosine levels and mechanisms by which it promotes tumor growth and broadly suppresses protective immunity, with extra focus on the attenuation of T cell function. Finally, we present an overview of promising pre-clinical and clinical approaches being explored for blocking the adenosine axis for enhanced control of solid tumors.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Cholera toxin enhances interleukin-17A production in both CD4+ and CD8+ cells via a cAMP/protein kinase A-mediated interleukin-17A promoter activation

Cholera toxin (CT) is a bacterial component that increases intracellular cAMP levels in host cells and suppresses T-cell activation. Recently, CT was reported to induce T helper type 17-skewing dendritic cells and activate interleukin-17A (IL-17A) production in CD4⁺ T cells through a cAMP-dependent pathway. However, the underlying mechanism by which cAMP regulates IL-17A production in T cells is not completely defined. In this study, we took advantage of a small molecule protein kinase A (PKA) inhibitor (H89) and different cAMP analogues: a PKA-specific activator (N6-benzoyl-adenosine-cAMP), an exchange protein activated by cAMP-specific activator (Rp-8-chlorophenylthio-2'-O-methyl cAMP), and a PKA inhibitor (Rp-8-bromo-cAMP), to elucidate the signalling cascade of cAMP in IL-17A regulation in T cells. We found that CT induced IL-17A production and IL-17A promoter activity in activated CD4⁺ T cells through a cAMP/PKA pathway. Moreover, this regulation was via cAMP-response element binding protein (CREB) -mediated transcriptional activation by using the transfection of an IL-17A promoter-luciferase reporter construct and CREB small interfering RNA in Jurkat cells. Also, we showed that CREB bound to the CRE motif located at -183 of the IL-17A promoter in vitro. Most interestingly, not only in CD4⁺ T cells, CT also enhanced cAMP/PKA-dependent IL-17A production and CREB phosphorylation in CD8⁺ T cells. In conclusion, our data suggest that CT induces an IL-17A-dominated immune microenvironment through the cAMP/PKA/CREB signalling pathway. Our study also highlights the potentials of CT and cAMP in modulating T helper type 17 responses in vivo.

Galectin-9 Is Critical for Mucosal Adaptive Immunity through the T Helper 17-IgA Axis

Impairment of the intestinal mucosal immunity significantly increases the risk of acute and chronic diseases. IgA plays a major role in humoral mucosal immunity to provide protection against pathogens and toxins in the gut. Here, we investigated the role of endogenous galectin-9, a tandem repeat-type β-galactoside-binding protein, in intestinal mucosal immunity. By mucosal immunization of Lgals9^-/- and littermate control mice, it was found that lack of galectin-9 impaired mucosal antigen-specific IgA response in the gut. Moreover, Lgals9^-/- mice were more susceptible to developing watery diarrhea and more prone to death in response to high-dose cholera toxin. The results indicate the importance of galectin-9 in modulating intestinal adaptive immunity. Furthermore, bone marrow chimera mice were established, and galectin-9 in hematopoietic cells was found to be critical for adaptive IgA response. In addition, immunized Lgals9^-/- mice exhibited lower expression of Il17 and fewer T helper 17 (Th17) cells in the lamina propria, implying that the Th17-IgA axis is involved in this mechanism. Taken together, these findings suggest that galectin-9 plays a role in mucosal adaptive immunity through the Th17-IgA axis. By manipulating the expression or activity of galectin-9, intestinal mucosal immune response can be altered and may benefit the development of mucosal vaccination.

Enhancing the toolbox to study IL-17A in cattle and sheep

The development of methods to detect cytokine expression by T cell subsets in ruminants is fundamental to strategic development of new livestock vaccines for prevention of infectious diseases. It has been possible to detect T cell expression of IFN-γ, IL-4 and IL-10 in ruminants for many years but methods to detect expression of IL-17A are relatively limited. To address this gap in capability we have cloned bovine and ovine IL-17A cDNAs and expressed biologically-active recombinant proteins in Chinese Hamster Ovary (CHO) cells. We used the transfected CHO cells to screen commercially-available antibodies for their ability to detect IL-17A expression intracellularly and in culture supernates. We demonstrate that an ELISA for bovine IL-17A detects native ovine IL-17A. Moreover, the constituent polyclonal antibodies (pabs) in the ELISA were used to enumerate peripheral blood mononuclear cells (PBMC) expressing IL-17A from cattle and sheep by ELISpot. We identified two monoclonal antibodies (mabs) that detect recombinant intracellular IL-17A in CHO cells by flow cytometry. One of these mabs was used to detect native intracellular IL-17A expression in PBMC in conjunction with cell surface phenotyping mabs [CD4+ve, CD8+ve and Workshop Cluster 1 (WC-1)+ve gamma-delta (γδ)] we show that distinct T cell subsets in cattle (defined as CD4+ve, CD8+ve or WC-1+ve) and sheep (defined as CD4+ve or WC-1+ve) can express IL-17A following activation. These novel techniques provide a solid basis to investigate IL-17A expression and define specific CD4+ve T cell subset activation in ruminants.

U-Omp19 from Brucella abortus Is a Useful Adjuvant for Vaccine Formulations against Salmonella Infection in Mice

Most pathogens infect through mucosal surfaces, and parenteral immunization typically fails to induce effective immune responses at these sites. Development of oral-administered vaccines capable of inducing mucosal as well as systemic immunity while bypassing the issues of antigen degradation and immune tolerance could be crucial for the control of enteropathogens. This study demonstrates that U-Omp19, a bacterial protease inhibitor with immunostimulatory features, coadministered with Salmonella antigens by the oral route, enhances mucosal and systemic immune responses in mice. U-Omp19 was able to increase antigen-specific production of IFN-γ and IL-17 and mucosal (IgA) antibody response. Finally, oral vaccination with U-Omp19 plus Salmonella antigens conferred protection against virulent challenge with Salmonella Typhimurium, with a significant reduction in bacterial loads. These findings prove the efficacy of this novel adjuvant in the Salmonella infection model and support the potential of U-Omp19 as a suitable adjuvant in oral vaccine formulations against mucosal pathogens requiring T helper (Th)1-Th17 protective immune responses.

Enhanced effect of BCG vaccine against pulmonary Mycobacterium tuberculosis infection in mice with lung Th17 response to mycobacterial heparin-binding hemagglutinin adhesin antigen

Although the BCG vaccine can prevent tuberculosis (TB) in infants, its ability to prevent adult pulmonary TB is reportedly limited. Therefore, development of a novel effective vaccine against pulmonary TB has become an international research priority. We have previously reported that intranasal vaccination of mice with a mycobacterial heparin-binding hemagglutinin adhesin (HBHA) plus mucosal adjuvant cholera toxin (CT) enhances production of IFN-γ and anti-HBHA antibody and suppresses extrapulmonary bacterial dissemination after intranasal infection with BCG. In the present study, the effects of intranasal HBHA + CT vaccine on murine pulmonary Mycobacterium tuberculosis (Mtb) infection were examined. Intranasal HBHA + CT vaccination alone failed to reduce the bacterial burden in the infected lung. However, a combination vaccine consisting of s.c. BCG priming and an intranasal HBHA + CT booster significantly enhanced protective immunity against pulmonary Mtb infection on day 14 compared with BCG vaccine alone. Further, it was found that intranasal HBHA + CT vaccine enhanced not only IFN-γ but also IL-17A production by HBHA-specific T cells in the lung after pulmonary Mtb infection. Therefore, this combination vaccine may be a good candidate for a new vaccine strategy against pulmonary TB.

Mechanisms of Cholera Toxin in the Modulation of TH17 Responses

Numerous studies have shown that TH17 cells and their signature cytokine IL-17A are critical to host defense against various bacterial and fungal infections. The protective responses mediated by TH17 cells and IL-17A include the recruitment of neutrophils, release of antimicrobial peptides and chemokines, and enhanced tight junction of epithelial cells. Due to the importance of TH17 cells in infections, efforts have been made to develop TH17-based vaccines. The goal of vaccination is to establish a protective immunological memory. Most currently approved vaccines are antibody-based and have limited protection against stereotypically different strains. Studies show that T-cell-based vaccines may overcome this limitation and protect hosts against infection of different strains. Two main strategies are used to develop TH17 vaccines: identification of TH17-specific antigens and TH17-skewing adjuvants. Studies have revealed that cholera toxin (CT) induces a potent Th17 response following vaccination. Antigen vaccination along with CT induces a robust TH17 response, which is sometimes accompanied by TH1 responses. Due to the toxicity of CT, it is hard to apply CT in a clinical setting. Thus, understanding how CT modulates TH17 responses may lead to the development of successful TH17-based vaccines.

Avidity of human T cell receptor engineered CD4(+) T cells drives T-helper differentiation fate

The role of the T cell receptor (TCR) in antigen recognition and activation of T lymphocytes is well established. However, how the TCR affects T-helper differentiation/skewing is less well understood, particularly for human CD4(+) (CD4) T cell subsets. Here we investigate the role of TCR specific antigen avidity in differentiation and maintenance of human Th1, Th2 and Th17 subsets. Two human TCRs, both specific for the same peptide antigen but with different avidities, were cloned and expressed in human CD4 T cells. These TCR engineered cells were then stimulated with specific antigen in unskewed and T-helper skewed conditions. We show that TCR avidity can control the percentage of IL-4 and IFN-γ co-expression in unskewed TCR engineered cells, that effector function can be maintained in a TCR avidity-dependent manner in skewed TCR engineered cells, and that increased TCR avidity can accelerate Th1 skewing of TCR engineered cells.

Interleukin-17A in lipid metabolism and atherosclerosis

Interleukin-17 (IL-17) A, the most important cytokine of the IL-17 family predominantly secreted by T helper 17 (Th17) cells, plays a critical role in the development of inflammatory diseases. Its receptor is an obligate heterodimer composed of IL-17 receptor (IL-17R) A and C, the main members of the IL-17R family. Binding of IL-17A to the IL-17RA/C complex can activate a variety of downstream signaling pathways such as nuclear factor kappa-B (NF-κB), activator protein 1 (AP1) and CCAAT/enhancer-binding protein (C/EBP) to induce the expression of proinflammatory cytokines and chemokines. IL-17A also promotes mRNA stability. Growing evidence shows that IL-17A is involved in lipid metabolism and the pathogenesis of atherosclerosis, a chronic inflammatory arterial disease driven by both innate and adaptive immune responses to modified lipoproteins. In the current review, we describe recent progress on regulation and signaling of IL-17A, and highlight its impacts on lipid metabolism and atherosclerosis.