CD8+ DC, but Not CD8(-)DC, isolated from BCG-infected mice reduces pathological reactions induced by mycobacterial challenge infection

Vaginal delivery of vaccines

Recent estimates suggest that one in two sexually active individuals will acquire a sexually transmitted infection by age 25, an alarming statistic that amounts to over 1 million new infections per day worldwide. Vaccination against STIs is highly desirable for alleviating this global burden of disease. Vaginal immunization is a promising strategy to combat transmission via the vaginal mucosa. The vagina is typically considered a poor inductive site for common correlates of adaptive immunity. However, emerging evidence suggests that immune tolerance may be overcome by precisely engineered vaccination schemes that orchestrate cell-mediated immunity and establish tissue resident memory immune cells. In this review, we will discuss the unique immunological milieu of the vaginal mucosa and our current understanding of correlates of pathogenesis and protection for several common STIs. We then present a summary of recent vaginal vaccine studies and explore the role that mucosal adjuvants and delivery systems play in enhancing protection according to requisite features of immunity. Finally, we offer perspectives on the challenges and future directions of vaginal vaccine delivery, discussing remaining physiological barriers and innovative vaccine formulations that may overcome them.

SND1 promotes Th1/17 immunity against chlamydial lung infection through enhancing dendritic cell function

To date, no reports have linked the multifunctional protein, staphylococcal nuclease domain-containing protein 1 (SND1), to host defense against intracellular infections. In this study, we investigated the role and mechanisms of SND1, by using SND1 knockout (SND1-/-) mice, in host defense against the lung infection of Chlamydia muridarum, an obligate intracellular bacterium. Our data showed that SND1-/- mice exhibited significantly greater body weight loss, higher organism growth, and more severe pathological changes compared with wild-type mice following the infection. Further analysis showed significantly reduced Chlamydia-specific Th1/17 immune responses in SND1-/- mice after infection. Interestingly, the dendritic cells (DCs) isolated from SND1-/- mice showed lower costimulatory molecules expression and IL-12 production, but higher IL-10 production compared with those from wild-type control mice. In the DC-T cell co-culture system, DCs isolated from SND1-/- infected mice showed significantly reduced ability to promote Chlamydia-specific IFN-γ producing Th1 cells but enhanced capacity to induce CD4+T cells into Foxp3+ Treg cells. Adoptive transfer of DCs isolated from SND1-/- mice, unlike those from wild-type control mice, failed to protect the recipients against challenge infection. These findings provide in vivo evidence that SND1 plays an important role in host defense against intracellular bacterial infection, and suggest that SND1 can promote Th1/17 immunity and inhibit the expansion of Treg cells through modulation of the function of DCs.

Flt3-L enhances trans-epithelial migration and antigen presentation of dendritic cells adoptively transferred to genital mucosa

Dendritic cells (DCs) play a critical role in shaping adaptive immunity. Systemic transfer of DCs by intravenous injection has been widely investigated to inform the development of immunogenic DCs for use as cellular therapies. Adoptive transfer of DCs to mucosal sites has been limited but serves as a valuable tool to understand the role of the microenvironment on mucosal DC activation, maturation and antigen presentation. Here, we show that chitosan facilitates transmigration of DCs across the vaginal epithelium in the mouse female reproductive tract (FRT). In addition, ex vivo programming of DCs with fms-related tyrosine kinase 3 ligand (Flt3-L) was found to enhance translocation of intravaginally administered DCs to draining lymph nodes (dLNs) and stimulate in vivo proliferation of both antigen-specific CD4+ and CD8+ T cells (cross-presentation). Mucosal priming with chitosan and DC programming may hold great promise to enhance efficacy of DC-based vaccination to the female genital mucosa.

IL-10 Dampens the Th1 and Tc Activation through Modulating DC Functions in BCG Vaccination

BCG, the only registered vaccine against Mycobacterial Tuberculosis (TB) infection, has been questioned for its protective efficacy for decades. Although lots of efforts were made to improve the BCG antigenicity, few studies were devoted to understand the role of host factors in the variability of the BCG protection. Using the IL-10KO mice and pulmonary tuberculosis infection model, we have addressed the role of IL-10 in the BCG vaccination efficacy. The data showed that IL-10-deficient dendritic cells (DCs) could promote the immune responses through upregulation of the surface costimulatory molecule expression and play an orchestra role through activating CD4⁺T cell. IL-10-deficient mice had higher IFN γ, TNF α, and IL-6 production after BCG vaccination, which was consistent with the higher proportion of IFN γ⁺CD3⁺, IFN γ⁺CD4⁺, and IFN γ⁺CD8⁺ T cells in the spleen. Particularly, the BCG-vaccinated IL-10KO mice showed less inflammation after TB challenge compared to WT mice, which was supported by the promoted Th1 and Tc, as well as the downregulated Treg responses in IL-10 deficiency. In a conclusion, we demonstrated the negative relationship between Th1/Tc responses with IL-10 production. IL-10 deficiency restored the type 1 immune response through DC activation, which provided better protection against TB infection. Hence, our study offers the first experimental evidence that, contrary to the modulation of BCG, host immunity plays a critical role in the BCG protective efficacy against TB.

Langerin+ CD8α+ Dendritic Cells Drive Early CD8+ T Cell Activation and IL-12 Production During Systemic Bacterial Infection

Bloodstream infections induce considerable morbidity, high mortality, and represent a significant burden of cost in health care; however, our understanding of the immune response to bacteremia is incomplete. Langerin⁺ CD8α⁺ dendritic cells (DCs), residing in the marginal zone of the murine spleen, have the capacity to cross-prime CD8⁺ T cells and produce IL-12, both of which are important components of antimicrobial immunity. Accordingly, we hypothesized that this DC subset may be a key promoter of adaptive immune responses to blood-borne bacterial infections. Utilizing mice that express the diphtheria toxin receptor under control of the langerin promoter, we investigated the impact of depleting langerin⁺ CD8α⁺ DCs in a murine model of intravenous infection with Mycobacterium bovis bacille Calmette–Guerin (BCG). In the absence of langerin⁺ CD8α⁺ DCs, the immune response to blood-borne BCG infection was diminished: bacterial numbers in the spleen increased, serum IL-12p40 decreased, and delayed CD8⁺ T cell activation, proliferation, and IFN-γ production was evident. Our data revealed that langerin⁺ CD8α⁺ DCs play a pivotal role in initiating CD8⁺ T cell responses and IL-12 production in response to bacteremia and may influence the early control of systemic bacterial infections.

Immune Responses in the Liver

The liver is a key, frontline immune tissue. Ideally positioned to detect pathogens entering the body via the gut, the liver appears designed to detect, capture, and clear bacteria, viruses, and macromolecules. Containing the largest collection of phagocytic cells in the body, this organ is an important barrier between us and the outside world. Importantly, as portal blood also transports a large number of foreign but harmless molecules (e.g., food antigens), the liver's default immune status is anti-inflammatory or immunotolerant; however, under appropriate conditions, the liver is able to mount a rapid and robust immune response. This balance between immunity and tolerance is essential to liver function. Excessive inflammation in the absence of infection leads to sterile liver injury, tissue damage, and remodeling; insufficient immunity allows for chronic infection and cancer. Dynamic interactions between the numerous populations of immune cells in the liver are key to maintaining this balance and overall tissue health.

CD103+ lung dendritic cells (LDCs) induce stronger Th1/Th17 immunity to a bacterial lung infection than CD11bhi LDCs

Recent studies suggest differential roles for CD103+ and CD11b^hi lung dendritic cells (LDCs) in host defense against viral and bacterial infections. In this study, we examined the contribution of these LDC subsets in protective immunity to chlamydial lung infection using a Chlamydia muridarum mouse infection model. We found that CD103+ LDCs showed higher expression of costimulatory molecules (CD40, CD80 and CD86) and increased production of cytokines (IL-12p70, IL-10, IL-23 and IL-6) compared with CD11b^hi LDCs, but the expression of programmed death-ligand 1 (PD-L1) was similar between the two subsets. More importantly, we found, in adoptive transfer experiments, that the mice receiving CD103+ LDCs from Chlamydia-infected mice exhibited better protection than the recipients of CD11b^hi LDCs, which was associated with more robust Th1/Th17 cytokine responses. In addition, in vitro experiments showed that CD103+ LDCs induced stronger IFN-γ and IL-17 responses, when cocutured with chlamydial antigen-primed CD4+ T cells, than CD11b^hi LDCs. Furthermore, the blockade of PD1 in the culture of CD4+ T cells with either CD103+ or CD11b^hi LDCs enhanced production of IFN-γ and IL-17. In conclusion, our data provide direct evidence that CD103+ LDCs are more potent in promoting Th1/Th17 immunity to chlamydial lung infection than CD11b^hi LDCs.

Novel T-cell epitopes on Schistosoma japonicum SjP40 protein and their preventive effect on allergic asthma in mice

Allergic asthma is a chronic inflammatory disease mediated by Th2 cell immune responses. Currently, immunotherapies based on immune deviation are attractive, preventive, and therapeutic strategies for asthma. Many studies have shown that intracellular bacterial infections such as mycobacteria and their components can suppress asthmatic reactions by enhancing Th1 responses, while helminth infections and their proteins can inhibit allergic asthma via immune regulation. However, some helminth proteins such as SmP40, the major egg antigen of Schistosoma mansoni, are found as Th1 type antigens. Using a panel of overlapping peptides, we identified T-cell epitopes on SjP40 protein of Schistosoma japonicum, which can induce Th1 cytokine and inhibit the production of Th2 cytokines and airway inflammation in a mouse model of allergic asthma. These results reveal a novel form of immune protective mechanism, which may play an important role in the modulating effect of helminth infection on allergic asthmatic reactions.

Subversion of mouse dendritic cell subset function by bacterial pathogens

Dendritic cells (DCs) play an important role as sentinels of the immune system in initiating and controlling the quality of adaptive immune responses. Located at entry points of the host they can sense and alert the body from dangers such as infection by pathogenic bacteria. Considering their strategic localization it is not surprising that DCs have evolved in a series of DC subtypes, which are well adapted to their microenvironment. Nowadays, the advent of the identification of specific DC subtypes has opened the way for the study of pathogen-DCs interactions and the involved mechanisms of these interactions. Due to key aspect of DCs, several bacterial pathogens have taken advantage of these cells and developed mechanisms to subvert DC function and thereby evade the immune system. This review brings recent insights into DC-pathogenic bacteria cross-talk using the mouse model of infection with an emphasis on DC subtypes.

Herpes Simplex Virus 1 Suppresses the Function of Lung Dendritic Cells via Caveolin-1

Caveolin-1 (Cav-1), the principal structural protein of caveolae, has been implicated as a regulator of virus-host interactions. Several viruses exploit caveolae to facilitate viral infections. However, the roles of Cav-1 in herpes simplex virus 1 (HSV-1) infection have not fully been elucidated. Here, we report that Cav-1 downregulates the expression of inducible nitric oxide synthase (iNOS) and the production of nitric oxide (NO) in dendritic cells (DCs) during HSV-1 infection. As a result, Cav-1 deficiency led to an accelerated elimination of virus and less lung pathological change following HSV-1 infection. This protection was dependent on iNOS and NO production in DCs. Adoptive transfer of DCs with Cav-1 knockdown was sufficient to confer the protection to wild-type (WT) mice. In addition, Cav-1 knockout (KO) (Cav-1(-/-)) mice treated with an iNOS inhibitor exhibited significantly reduced survival compared to that of the nontreated controls. We found that Cav-1 colocalized with iNOS and HSV-1 in caveolae in HSV-1-infected DCs, suggesting their interaction. Taken together, our results identified Cav-1 as a novel regulator utilized by HSV-1 to evade the host antiviral response mediated by NO production. Therefore, Cav-1 might be a valuable target for therapeutic approaches against herpesvirus infections.

Immune surveillance by the liver

Receiving both portal vein blood and arterial blood, the liver is an important and critical component in the defense against blood-borne infection. To accomplish this role, the liver contains numerous innate and adaptive immune cells that specialize in detection and capture of pathogens from the blood. Further, these immune cells participate in coordinated immune responses leading to pathogen clearance, leukocyte recruitment and antigen presentation to lymphocytes within the vasculature. Finally, this role in host defense must be tightly regulated to ensure that inappropriate immune responses are not raised against nonpathogenic exogenous blood-borne molecules, such as those derived from food. It is this balance between activation and tolerance that characterizes the liver as a frontline immunological organ.

Protection to respiratory challenge of Brucella abortus strain 2308 in the lung

Brucella is amongst the top 5 causes of zoonotic disease worldwide. Infection is through ingestion, inhalation or contact exposure. Brucella is characterized as a class B pathogen by Centers of Disease Control and Prevention (CDC). Currently, there are no efficacious vaccines available in people. Currently available USDA approved vaccines for animals include B. abortus strain RB51 and B. melitensis Rev1. Protection is mediated by a strong innate and CD4 Th1, CD8 Tc1 immune response. If protective vaccines can be developed, disease in people and animals can be controlled. While strain RB51 protects in cattle, and against intraperitoneal challenge in mice, it does not protect against respiratory challenge. Therefore, we assessed the efficacy of strain RB51 combined with different TLR agonists, and O-side chain from LPS, to enhance protection against respiratory challenge with strain 2308. We hypothesized that TLR agonists and O-side chain would enhance protection. Strains RB51 with TLR2 agonist, RB51 with TLR4 agonist and strain 19 provided significant protection in the lung. Protection using strain RB51 with TLR agonists was associated with increased IgG2a and IgG1 in the (bronchoalveolar lavage) BAL and serum, and increased IgA (serum). Splenocytes from strain RB51 with TLR2 vaccinated mice up-regulated antigen specific interferon-gamma and TNF-alpha production. Vaccination and challenge resulted in significant increases in activated dendritic cells (DCs), and increased CD4 and CD8 cells in the BAL. Overall, this study demonstrates the ability of TLR agonists 2 and 4 to up-regulate strain RB51 mediated protection in the lung to respiratory challenge against strain 2308.

Dendritic cell subsets in mycobacterial infection: control of bacterial growth and T cell responses

Anti-mycobacterial immunity is guided by specialised antigen presenting cells known as dendritic cells, which are essential for both initiating and maintaining T cell immune responses during infection. The dendritic cell population can be divided into functionally distinct subsets that differ in their ability to present antigen and produce key TH1 cytokines, such as IL-12. This review discusses recent studies, in murine models, investigating which dendritic cell populations are important for mycobacterial control.

Activated protein C targets CD8+ dendritic cells to reduce the mortality of endotoxemia in mice

Activated protein C (aPC) therapy reduces mortality in adult patients with severe sepsis. In mouse endotoxemia and sepsis models, mortality reduction requires the cell signaling function of aPC, mediated through protease-activated receptor-1 (PAR1) and endothelial protein C receptor (EPCR; also known as Procr). Candidate cellular targets of aPC include vascular endothelial cells and leukocytes. Here, we show that expression of EPCR and PAR1 on hematopoietic cells is required in mice for an aPC variant that mediates full cell signaling activity but only minimal anticoagulant function (5A-aPC) to reduce the mortality of endotoxemia. Expression of EPCR in mature murine immune cells was limited to a subset of CD8+ conventional dendritic cells. Adoptive transfer of splenic CD11chiPDCA-1- dendritic cells from wild-type mice into animals with hematopoietic EPCR deficiency restored the therapeutic efficacy of aPC, whereas transfer of EPCR-deficient CD11chi dendritic cells or wild-type CD11chi dendritic cells depleted of EPCR+ cells did not. In addition, 5A-aPC inhibited the inflammatory response of conventional dendritic cells independent of EPCR and suppressed IFN-gamma production by natural killer-like dendritic cells. These data reveal an essential role for EPCR and PAR1 on hematopoietic cells, identify EPCR-expressing dendritic immune cells as a critical target of aPC therapy, and document EPCR-independent antiinflammatory effects of aPC on innate immune cells.