Mechanisms of Cholera Toxin in the Modulation of TH17 Responses

Migratory CD103+CD11b+ cDC2s in Peyer's patches are critical for gut IgA responses following oral immunization

Induction and regulation of specific intestinal immunoglobulin (Ig)A responses critically depend on dendritic cell (DC) subsets and the T cells they activate in the Peyer's patches (PP). We found that oral immunization with cholera toxin (CT) as an adjuvant resulted in migration-dependent changes in the composition and localization of PP DC subsets with increased numbers of cluster of differentiation (CD)103- conventional DC (cDC)2s and lysozyme-expressing DC (LysoDCs) in the subepithelial dome and of CD103+ cDC2s that expressed CD101 in the T cell zones, while oral ovalbumin (OVA) tolerization was instead associated with greater accumulation of cDC1s and peripherally induced regulatory T cells (pTregs) in this area. Decreased IgA responses were observed after CT-adjuvanted immunization in huCD207DTA mice lacking CD103+ cDC2s, while oral OVA tolerization was inefficient in cDC1-deficient Batf3-/- mice. Using OVA transgenic T cell receptor CD4 T cell adoptive transfer models, we found that co-transferred endogenous wildtype CD4 T cells can hinder the induction of OVA-specific IgA responses through secretion of interleukin-10. CT could overcome this blocking effect, apparently through a modulating effect on pTregs while promoting an expansion of follicular helper T cells. The data support a model where cDC1-induced pTreg normally suppresses PP responses for any given antigen and where CT's oral adjuvanticity effect is dependent on promoting follicular helper T cell responses through induction of CD103+ cDC2s.

Modulation of Host-Microbe Metabolism by Cholera Toxin

In order for successful fecal-oral transmission, enteric bacterial pathogens have to successfully compete with the intestinal microbiota and reach high concentrations during infection. Vibrio cholerae requires cholera toxin (CT) to cause diarrheal disease, which is thought to promote the fecal-oral transmission of the pathogen. Besides inducing diarrheal disease, the catalytic activity of CT also alters host intestinal metabolism, which promotes the growth of V. cholerae during infection through the acquisition of host-derived nutrients. Furthermore, recent studies have found that CT-induced disease activates a niche-specific suite of V. cholerae genes during infection, some of which may be important for fecal-oral transmission of the pathogen. Our group is currently exploring the concept that CT-induced disease promotes the fecal-oral transmission of V. cholerae by modulating both host and pathogen metabolism. Furthermore, the role of the intestinal microbiota in pathogen growth and transmission during toxin-induced disease merits further investigation. These studies open the door to investigating whether other bacterial toxins also enhance pathogen growth and transmission during infection, which may shed light on the design of novel therapeutics for intervention or prevention of diarrheal diseases.

UCP3 reciprocally controls CD4+ Th17 and Treg cell differentiation

Uncoupling proteins (UCPs) are members of the mitochondrial anion carrier superfamily that can mediate the transfer of protons into the mitochondrial matrix from the intermembrane space. We have previously reported UCP3 expression in thymocytes, mitochondria of total splenocytes and splenic lymphocytes. Here, we demonstrate that Ucp3 is expressed in peripheral naive CD4⁺ T cells at the mRNA level before being markedly downregulated following activation. Non-polarized, activated T cells (Th0 cells) from Ucp3^-/- mice produced significantly more IL-2, had increased expression of CD25 and CD69 and were more proliferative than Ucp3^+/+ Th0 cells. The altered IL-2 expression observed between T cells from Ucp3^+/+ and Ucp3^-/- mice may be a factor in determining differentiation into Th17 or induced regulatory (iTreg) cells. When compared to Ucp3^+/+, CD4⁺ T cells from Ucp3^-/- mice had increased FoxP3 expression under iTreg conditions. Conversely, Ucp3^-/- CD4⁺ T cells produced a significantly lower concentration of IL-17A under Th17 cell-inducing conditions in vitro. These effects were mirrored in antigen-specific T cells from mice immunized with KLH and CT. Interestingly, the altered responses of Ucp3^-/- T cells were partially reversed upon neutralisation of IL-2. Together, these data indicate that UCP3 acts to restrict the activation of naive T cells, acting as a rheostat to dampen signals following TCR and CD28 co-receptor ligation, thereby limiting early activation responses. The observation that Ucp3 ablation alters the Th17:Treg cell balance in vivo as well as in vitro suggests that UCP3 is a potential target for the treatment of Th17 cell-mediated autoimmune diseases.

A Systemic Prime-Intrarectal Pull Strategy Raises Rectum-Resident CD8+ T Cells for Effective Protection in a Murine Model of LM-OVA Infection

As the entry sites of many pathogens such as human immunodeficiency virus (HIV), mucosal sites are defended by rapidly reacting resident memory T cells (TRM). TRMs represent a special subpopulation of memory T cells that persist long term in non-lymphoid sites without entering the circulation and provide the “sensing and alarming” role in the first-line defense against infection. The rectum and vagina are the two primary mucosal portals for HIV entry. However, compared to vaginal TRM, rectal TRM is poorly understood. Herein, we investigated the optimal vaccination strategy to induce rectal TRM. We identified an intranasal prime–intrarectal boost (pull) strategy that is effective in engaging rectal TRM alongside circulating memory T cells and demonstrated its protective efficacy in mice against infection of Listeria monocytogenes. On the contrary, the same vaccine delivered via either intranasal or intrarectal route failed to raise rectal TRM, setting it apart from vaginal TRM, which can be induced by both intranasal and intrarectal immunizations. Moreover, intramuscular prime was also effective in inducing rectal TRM in combination with intrarectal pull, highlighting the need of a primed systemic T cell response. A comparison of different pull modalities led to the identification that raising rectal TRM is mainly driven by local antigen presence. We further demonstrated the interval between prime and boost steps to be critical for the induction of rectal TRM, revealing circulating recently activated CD8+ T cells as the likely primary pullable precursor of rectal TRM. Altogether, our studies lay a new framework for harnessing rectal TRM in vaccine development.

Construction and Immunogenicity of Recombinant Vaccinia Virus Vaccine Against Japanese Encephalitis and Chikungunya Viruses Infection in Mice

Japanese encephalitis virus (JEV) is recognized as a public health risk by the World Health Organization. In Asia, each year, ∼70,000 people become infected with JEV, which results in ∼10,000 deaths. Chikungunya virus (CHIKV) is an RNA virus, whose infection mainly causes fever, myalgia, and skin rash. Although the mortality rate is low, it seriously affects daily life. JEV and CHIKV infect humans through mosquitoes; therefore, a recombinant vaccinia virus coexpressing JEV E and CHIKV E1 proteins was constructed to prevent their concurrent infection. In this study, after mice first immunization, booster immunization was performed at 21 days postimmunization (dpi). At 35 dpi, mice were challenged with JEV and CHIKV. Specific antibodies significantly increased in the rVTT-CE1-JE-EGFP group, which were significantly (p < 0.01) higher than those of the control groups at 35 dpi. The plaque reduction neutralization tests (JEV) of rVTT-CE1-JE-EGFP group was 1:320 at 35 dpi. Furthermore, cytokine levels and the percentage of CD3⁺CD4⁺ and CD3⁺CD8⁺ T-lymphocytes in the rVTT-CE1-JE-EGFP group were significantly (p < 0.01) higher than those in the control groups at 35 dpi. After challenge, mice body weights in rVTT-CE1-JE-EGFP group were not significantly altered, and the survival rate was 100%. These results showed the rVTT-CE1-JE-EGFP group elicited significant humoral and cellular immune responses, thus indicating that the recombinant vaccine may serve as a candidate for effective prevention of CHIKV and JEV infection.

Generating mucosal and systemic immune response following vaccination of vibrio cholerae adhesion molecule against shigella flexneri infection

Introduction

Previous studies have shown 37.8 kDa pili subunit protein of Vibrio cholerae and 49.8 kDa pili subunit protein of Shigella flexneri can act as an adhesion molecule to initiate infection. These molecules also have the ability to agglutinate blood. The present study assessed mucosal and systemic immunity following vaccination using 37.8 kDa V. cholerae and protection against S. flexneri.

Subjects and Methods

Haemagglutination test was performed after purification of V. cholerae protein, followed by an anti-haemagglutination test. The intestinal weight and colony count were used to validate the protective effect on balb/c mice which were divided into the naive group, Shigella-positive control group, Vibrio-positive control group, V. cholerae infected-Vibrio-vaccinated group and S. flexneri-infected-Vibrio-vaccinated group. Th17, Treg, interleukin (IL) IL-17A, β-defensin and secretory-immunoglobulin A (s-IgA) were also measured to determine the systemic and mucosal immunity after vaccination.

Results

The haemagglutination and anti-haemagglutination tests showed that the 37.8 kDa protein could inhibit 49.8 kDa of the S. flexneri pili subunit. Decreased intestinal weight and colony count of vaccinated group compared to naive group also support cross reaction findings. Vaccination also generates higher level of Th17, Treg, IL-17A, β-defensin and s-IgA significantly.

Conclusions

37.8 kDa subunit pili can act as a homologous vaccine candidate to prevent V. cholerae and S. flexneri infection.

Direct Manipulation of T Lymphocytes by Proteins of Gastrointestinal Bacterial Pathogens

Gastrointestinal bacterial infection represents a significant threat to human health, as well as a burden on food animal production and welfare. Although there is advanced knowledge about the molecular mechanisms underlying pathogenesis, including the development of immune responses to these pathogens, gaps in knowledge persist. It is well established that gastrointestinal bacterial pathogens produce a myriad of proteins that affect the development and effectiveness of innate immune responses. However, relatively few proteins that directly affect lymphocytes responsible for humoral or cell-mediated immunity and memory have been identified. Here, we review factors produced by gastrointestinal bacterial pathogens that have direct T cell interactions and what is known about their functions and mechanisms of action. T cell-interacting bacterial proteins that have been identified to date mainly target three major T cell responses: activation and expansion, chemotaxis, or apoptosis. Further, the requirement for more focused studies to identify and understand additional mechanisms used by bacteria to directly affect the T cell immune response and how these may contribute to pathogenesis is highlighted. Increased knowledge in this area will help to drive development of better interventions in prevention and treatment of gastrointestinal bacterial infection.

Sublingual immunization with Japanese encephalitis virus vaccine effectively induces immunity through both cellular and humoral immune responses in mice

The Japanese encephalitis virus (JEV) is the leading cause of viral encephalitis. Although there are four classes of vaccines against JEV, all of them are administered by s.c or i.m injection. Here, the effectiveness of sublingual (s.l.) administration of a JEV live-attenuated vaccine or recombinant modified vaccinia virus Ankara (MVA) vaccine, including JEV prM/E, was investigated. The mice were immunized three times i.m. or s.c. One week after the final immunization by both s.l. and i.m. routes, the titers of IgG1 induced by the recombinant MVA vaccine were higher than those induced by the live-attenuated vaccine, whereas the titers of IgG2a induced by the live-attenuated vaccine were higher than those induced by the recombinant MVA vaccine. However, both vaccines induced neutralizing antibodies when given by either s.l. or i.m. routes, indicating that both vaccines induce appropriate Th1 and Th2 cell responses through the s.l. and i.m. routes. Moreover, both vaccines protected against induction of proinflammatory cytokines and focal spleen white pulp hyperplasia after viral challenge. Virus-specific IFN-γ⁺ CD4⁺ and CD8⁺ T cells appeared to increase in mice immunized via both s.l. and i.m. routes. Interestingly, virus-specific IL-17⁺ CD4⁺ T cells increased significantly only in the mice immunized via the s.l. route; however, the increased IL-17 did not affect pathogenicity after viral challenge. These results suggest that s.l. immunization may be as useful as i.m. injection for induction of protective immune responses against JEV by both live-attenuated and recombinant MVA vaccines.