Vaccination route can significantly alter the innate lymphoid cell subsets: a feedback between IL-13 and IFN-γ

Location versus ID: what matters to lung-resident memory T cells?

Tissue-resident memory T cells (TRM cells) are vital for the promotion of barrier immunity. The lung, a tissue constantly exposed to foreign pathogenic or non-pathogenic antigens, is not devoid of these cells. Lung TRM cells have been considered major players in either the protection against respiratory viral infections or the pathogenesis of lung allergies. Establishment of lung TRM cells rely on intrinsic and extrinsic factors. Among the extrinsic regulators of lung TRM cells, the magnitude of the impact of factors such as the route of antigen entry or the antigen natural tropism for the lung is not entirely clear. In this perspective, we provide a summary of the literature covering this subject and present some preliminary results on this potential dichotomy between antigen location versus antigen type. Finally, we propose a hypothesis to synthesize the potential contributions of these two variables for lung TRM cell development.

Mucosal immune responses to infection and vaccination in the respiratory tract

The lungs are constantly exposed to inhaled debris, allergens, pollutants, commensal or pathogenic microorganisms, and respiratory viruses. As a result, innate and adaptive immune responses in the respiratory tract are tightly regulated and are in continual flux between states of enhanced pathogen clearance, immune-modulation, and tissue repair. New single-cell-sequencing techniques are expanding our knowledge of airway cellular complexity and the nuanced connections between structural and immune cell compartments. Understanding these varied interactions is critical in treatment of human pulmonary disease and infections and in next-generation vaccine design. Here, we review the innate and adaptive immune responses in the lung and airways following infection and vaccination, with particular focus on influenza virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The ongoing SARS-CoV-2 pandemic has put pulmonary research firmly into the global spotlight, challenging previously held notions of respiratory immunity and helping identify new populations at high risk for respiratory distress.

LUNG group 2 innate lymphoid cells as a new adjuvant target to enhance intranasal vaccine efficacy against influenza

Group 2 innate lymphoid cells (ILC2) are a relatively new class of innate immune cells. Lung ILC2 are early responders that secrete type 2 cytokines in response to danger ‘alarmin’ signals such as interleukin (IL)‐33 and thymic stromal lymphopoietin. Being an early source of type 2 cytokines, ILC2 are a critical regulator of type 2 immune cells of both innate and adaptive immune responses. The immune regulatory functions of ILC2 were mostly investigated in diseases where T helper 2 inflammation predominates. However, in recent years, it has been appreciated that the role of ILC2 extends to other pathological conditions such as cancer and viral infections. In this review, we will focus on the potential role of lung ILC2 in the induction of mucosal immunity against influenza virus infection and discuss the potential utility of ILC2 as a target for mucosal vaccination.

Evaluation of Innate Lymphoid Cells and Dendritic Cells Following Viral Vector Vaccination

Recently, we have shown that fate of a vaccine is determined by the cytokine milieu in the innate immune compartment at the early stage of vaccination. Specifically, 24 h post-delivery, level of innate lymphoid cell type 2 (ILC2)-derived IL-13/IL-13Rα2 are the master regulators of DC and also different ILC subsets responsible for modulating the downstream immune outcomes. Here, we provide step-by-step details how to assess different ILC and DC subsets in lung and muscle following intranasal and intramuscular viral vector vaccination, respectively, using multi-color flow cytometry and confocal microscopy.

Antishock Characteristics of Erythrocyte-mediated Endoplasmic Reticulum Stress in Macrophages in Severe Hemorrhagic Shock Environment Based on TLR9-cGAS-STING-IFN Signal Axis

This study aimed to investigate the protective effects of erythrocyte-mediated endoplasmic reticulum (ER) stress in macrophages in hemorrhagic shock. An hemorrhagic shock model was established in male BALB/c mice. Animals were randomly divided into three groups (n = 8): control group (A), erythrocyte reinfusion group (B), and TLR9 inhibition group (C). Eight healthy BALB/c mice were also included as group N (n = 8). Mice in group A were not treated, while mice in groups B and C were transfused with red blood cells separated from the blood of mice in group N. Flow cytometry was used to detect the expression of erythrocyte surface protein TLR9 in each group. Immunofluorescence assay was used to analyze the distribution and relative expression of protein STING in macrophages. Flow cytometry was used to analyze the expression of STING, ATF6, and IRE1 in macrophages. Enzyme-linked immunosorbent assay was used to analyze the levels of inflammatory signal molecules, including IFN-α, IFN-β, IL-6, CCL4, CCL5, and IL-6. FITC-Annexin V was used to analyze the apoptosis of immune cells (macrophages) in mouse blood samples and to detect the concentration of calcium ions in erythrocyte cytoplasm. The results showed that the expression of erythrocyte surface protein TLR9; the distribution of STING-positive cells in macrophages; the expressions of STING, ATF6, and IRE1 in macrophages; the levels of inflammatory signal molecules; the apoptosis rate of macrophages; and the intracellular calcium concentration in erythrocytes in group B were higher than those in group A, followed by group C. These results suggest that TLR9 regulates ER stress in macrophages of mice with hemorrhagic shock through the TLR9-cGAS-STING-IFN signaling pathway. Increased expression of TLR9 enhanced macrophage activity, reduced apoptosis, enhanced inflammatory response and immune response, and restored electrolyte level, which might be a therapeutic option for the treatment of hemorrhagic shock.

STAT3 determines IL-4 signalling outcomes in naïve T cells

IL-4 production is associated with low-avidity, poorly cytotoxic T cell induction that contributes to viral immune evasion and the failure of T cell-based vaccines. Yet, the precise mechanisms that regulate IL-4 signalling in T cells remain elusive. Mounting evidence indicates that cells can dynamically alter their IL-4/IL-13 receptor signature to modulate downstream immune outcomes upon pathogen encounter. Here, we describe how naïve (CD62L⁺CD44^lo-mid) CD4 and CD8 T cells distinctly engage both STAT6 and STAT3 in response to IL-4. We further show that IL-4R⍺ expression is both time- and IL-4 concentration-dependent. Remarkably, our findings reveal that STAT3 inhibition can ablate IL-4R⍺ and affect transcriptional expression of other Stat and Jak family members. By extension, the loss of STAT3 lead to aberrant STAT6 phosphorylation, revealing an inter-regulatory relationship between the two transcription factors. Moreover, IL-4 stimulation down-regulated TGF-β1 and IFN-γR1 expression on naïve T cells, possibly signifying the broad regulatory implications of IL-4 in conditioning lineage commitment decisions during early infection. Surprisingly, naïve T cells were unresponsive to IL-13 stimulation, unlike dendritic cells. Collectively, these findings could be exploited to inform more efficacious vaccines, as well as design treatments against IL-4/IL-13-associated disease conditions.

IL-13Rα2 Regulates the IL-13/IFN-γ Balance during Innate Lymphoid Cell and Dendritic Cell Responses to Pox Viral Vector-Based Vaccination

We have shown that manipulation of IL-13 and STAT6 signaling at the vaccination site can lead to different innate lymphoid cell (ILC)/dendritic cell (DC) recruitment, resulting in high avidity/poly-functional T cells and effective antibody differentiation. Here we show that permanent versus transient blockage of IL-13 and STAT6 at the vaccination site can lead to unique ILC-derived IL-13 and IFN-γ profiles, and differential IL-13Rα2, type I and II IL-4 receptor regulation on ILC. Specifically, STAT6-/- BALB/c mice given fowl pox virus (FPV) expressing HIV antigens induced elevated ST2/IL-33R+ ILC2-derived IL-13 and reduced NKp46+/- ILC1/ILC3-derived IFN-γ expression, whilst the opposite (reduced IL-13 and elevated IFN-γ expression) was observed during transient inhibition of STAT6 signaling in wild type BALB/c mice given FPV-HIV-IL-4R antagonist vaccination. Interestingly, disruption/inhibition of STAT6 signaling considerably impacted IL-13Rα2 expression by ST2/IL-33R+ ILC2 and NKp46- ILC1/ILC3, unlike direct IL-13 inhibition. Consistently with our previous findings, this further indicated that inhibition of STAT6 most likely promoted IL-13 regulation via IL-13Rα2. Moreover, the elevated ST2/IL-33R+ IL-13Rα2+ lung ILC2, 24 h post FPV-HIV-IL-4R antagonist vaccination was also suggestive of an autocrine regulation of ILC2-derived IL-13 and IL-13Rα2, under certain conditions. Knowing that IL-13 can modulate IFN-γ expression, the elevated expression of IFN-γR on lung ST2/IL-33R+ ILC2 provoked the notion that there could also be inter-regulation of lung ILC2-derived IL-13 and NKp46- ILC1/ILC3-derived IFN-γ via their respective receptors (IFN-γR and IL-13Rα2) at the lung mucosae early stages of vaccination. Intriguingly, under different IL-13 conditions differential regulation of IL-13/IL-13Rα2 on lung DC was also observed. Collectively these findings further substantiated that IL-13 is the master regulator of, not only DC, but also different ILC subsets at early stages of viral vector vaccination, and responsible for shaping the downstream adaptive immune outcomes. Thus, thoughtful selection of vaccine strategies/adjuvants that can manipulate IL-13Rα2, and STAT6 signaling at the ILC/DC level may prove useful in designing more efficacious vaccines against different/chronic pathogens.

Vaccine Inoculation Route Modulates Early Immunity and Consequently Antigen-Specific Immune Response

Vaccination is one of the most efficient public healthcare measures to fight infectious diseases. Nevertheless, the immune mechanisms induced in vivo by vaccination are still unclear. The route of administration, an important vaccination parameter, can substantially modify the quality of the response. How the route of administration affects the generation and profile of immune responses is of major interest. Here, we aimed to extensively characterize the profiles of the innate and adaptive response to vaccination induced after intradermal, subcutaneous, or intramuscular administration with a modified vaccinia virus Ankara model vaccine in non-human primates. The adaptive response following subcutaneous immunization was clearly different from that following intradermal or intramuscular immunization. The subcutaneous route induced a higher level of neutralizing antibodies than the intradermal and intramuscular vaccination routes. In contrast, polyfunctional CD8+ T-cell responses were preferentially induced after intradermal or intramuscular injection. We observed the same dichotomy when analyzing the early molecular and cellular immune events, highlighting the recruitment of cell populations, such as CD8+ T lymphocytes and myeloid-derived suppressive cells, and the activation of key immunomodulatory gene pathways. These results demonstrate that the quality of the vaccine response induced by an attenuated vaccine is shaped by early and subtle modifications of the innate immune response. In this immunization context, the route of administration must be tailored to the desired type of protective immune response. This will be achieved through systems vaccinology and mathematical modeling, which will be critical for predicting the efficacy of the vaccination route for personalized medicine.

Interleukin-13 as a target to alleviate severe coronavirus disease 2019 and restore lung homeostasis

The ongoing coronavirus disease (COVID-19) pandemic urgently requires the availability of interventions that improve outcomes for those with severe disease. Since severe acute respiratory syndrome coronavirus 2 infection is characterized by dysregulated lung mucosae, and that mucosal homeostasis is heavily influenced by interleukin (IL)-13 activity, we explore recent findings indicating that IL-13 production is proportional to disease severity. We propose that excessive IL-13 contributes to the progression of severe/fatal COVID-19 by (1) promoting the recruitment of immune cells that express inflammatory cytokines, causing a cytokine storm that results in widespread destruction of lung tissue, (2) directly facilitating tissue-remodeling that causes airway hyperinflammation and obstruction, and (3) diverting the immune system away from developing high-quality cytotoxic T cells that confer effective anti-viral immunity. These factors may cumulatively result in significant lung distress, multi-organ failure, and death. Here, we suggest repurposing existing IL-13-inhibiting interventions, including antibody therapies routinely used for allergic lung hyperinflammation, as well as viral vector-based approaches, to alleviate disease. Since many of these strategies have previously been shown to be both safe and effective, this could prove to be a highly cost-effective solution.

Relevance for Patients

There remains a desperate need to establish medical interventions that reliably improves outcomes for patients suffering from COVID-19. We explore the role of IL-13 in maintaining homeostasis at the lung mucosae and propose that its dysregulation during viral infection may propagate the hallmarks of severe disease - further exploration may provide a platform for invaluable therapeutics.

Mucosal IL-4R antagonist HIV vaccination with SOSIP-gp140 booster can induce high-quality cytotoxic CD4+/CD8+ T cells and humoral responses in macaques

Inducing humoral, cellular and mucosal immunity is likely to improve the effectiveness of HIV-1 vaccine strategies. Here, we tested a vaccine regimen in pigtail macaques using an intranasal (i.n.) recombinant Fowl Pox Virus (FPV)-gag pol env-IL-4R antagonist prime, intramuscular (i.m.) recombinant Modified Vaccinia Ankara Virus (MVA)-gag pol-IL-4R antagonist boost followed by an i.m SOSIP-gp140 boost. The viral vector-expressed IL-4R antagonist transiently inhibited IL-4/IL-13 signalling at the vaccination site. The SOSIP booster not only induced gp140-specific IgG, ADCC (antibody-dependent cellular cytotoxicity) and some neutralisation activity, but also bolstered the HIV-specific cellular and humoral responses. Specifically, superior sustained systemic and mucosal HIV Gag-specific poly-functional/cytotoxic CD4⁺ and CD8⁺ T cells were detected with the IL-4R antagonist adjuvanted strategy compared to the unadjuvanted control. In the systemic compartment elevated Granzyme K expression was linked to CD4⁺ T cells, whilst Granzyme B/TIA-1 to CD8⁺ T cells. In contrast, the cytotoxic marker expression by mucosal CD4⁺ and CD8⁺ T cells differed according to the mucosal compartment. This vector-based mucosal IL-4R antagonist/SOSIP booster strategy, which promotes cytotoxic mucosal CD4⁺ T cells at the first line of defence, and cytotoxic CD4⁺ and CD8⁺ T cells plus functional antibodies in the blood, may prove valuable in combating mucosal infection with HIV-1 and warrants further investigation.

Unique IL-13Rα2/STAT3 mediated IL-13 regulation detected in lung conventional dendritic cells, 24 h post viral vector vaccination

This study demonstrates that 24 h following viral vector-based vaccination IL-13Rα2 functions as a master sensor on conventional dendritic cells (cDCs), abetted by high protein stability coupled with minimal mRNA expression, to rapidly regulate DC mediated IL-13 responses at the lung mucosae, unlike IL-13Rα1. Under low IL-13, IL-13Rα2 performs as a primary signalling receptor, whilst under high IL-13, acts to sequester IL-13 to maintain homeostasis, both in a STAT3-dependent manner. Likewise, we show that viral vector-derived IL-13 levels at the vaccination site can induce differential STAT3/STAT6 paradigms in lung cDC, that can get regulated collaboratively or independently by TGF-β1 and IFN-γ. Specifically, low IL-13 responses associated with recombinant Fowlpox virus (rFPV) is regulated by early IL-13Rα2, correlated with STAT3/TGF-β1 expression. Whilst, high IL-13 responses, associated with recombinant Modified Vaccinia Ankara (rMVA) is regulated in an IL-13Rα1/STAT6 dependent manner associated with IFN-γR expression bias. Different viral vaccine vectors have previously been shown to induce unique adaptive immune outcomes. Taken together current observations suggest that IL-13Rα2-driven STAT3/STAT6 equilibrium at the cDC level may play an important role in governing the efficacy of vector-based vaccines. These new insights have high potential to be exploited to improve recombinant viral vector-based vaccine design, according to the pathogen of interest and/or therapies against IL-13 associated disease conditions.

Tissue-resident innate immunity in the lung

The lung is a unique organ that must protect against inhaled pathogens and toxins, without mounting a disproportionate response against harmless particulate matter and without compromising its vital function. Tissue-resident immune cells within the lung provide local immunity and protection from infection but are also responsible for causing disease when dysregulated. There is a growing appreciation of the importance of tissue-resident memory T cells to lung immunity, but non-recirculating, tissue-resident, innate immune cells also exist. These cells provide the first line of defence against pulmonary infection and are essential for co-ordinating the subsequent adaptive response. In this review, we discuss the main lung-resident innate immune subsets and their functions in common pulmonary diseases, such as influenza, bacterial pneumonia, asthma and inflammatory disorders.

A hierarchical role of IL-25 in ILC development and function at the lung mucosae following viral-vector vaccination

This study demonstrates that modulation of IL-25 and IL-33 cytokines responsible for innate lymphoid cell 2 (ILC2) activation/function can differentially regulate ILC profiles at the vaccination site, in a vaccine route-dependent manner. Specifically, recombinant fowlpox (rFPV) vector-based vaccine co-expressing an adjuvant that transiently sequestered IL-25 (FPV-HIV-IL-25 binding protein), delivered intramuscularly (i.m.) was able to induce significantly lower IL-25R⁺ ILC2-deived IL-13 and ILC1/ILC3-derived IFN-γ expression with significantly elevated IL-17A in muscle. In contrast, intranasal (i.n.) delivery was able to induce all three known ILC2 subsets (ST2/IL-33R⁺, IL-25R⁺, and TSLPR⁺ ILC2) to express varying amounts of IL-13 in lung, and also the TSLPR⁺ ILC2 to express IL-4, unlike the unadjuvanted control, which only showed ST2/IL-33R⁺ ILC2 to express IL-13. Interestingly, the sequestration of IL-25 in lung also induced a unique lineage⁻ ST2/IL-33R⁻ IL-25R⁻ TSLPR⁻ ILC2 population to express elevated IL-13 and IL-4. Moreover, both i.m. and, i.n. FPV-HIV-IL-25BP vaccination induced significantly elevated ILC1/ILC3-derived IL-17A in lung, indicating that ILC2 could directly impact ILC1/ILC3 activity. To our surprise, transient sequestration of IL-33 at the lung mucosae did not alter the lung ILC2 profiles or activity. These inhibitor studies showed that in the context of i.n. viral vector vaccination, IL-25 plays a predominant role in early ILC development/regulation than IL-33, and likely acts as a master regulator of ILC. Our previous findings have indicated that level of IL-4/IL-13 at the vaccination site impacts the quality/avidity of T cell immunity. Taken together data suggest that IL-25 binding protein could be used as an effective i.m. not an i.n. adjuvant to enhance quality of vaccine-specific T cell immunity. These findings evoke the notion that route-dependent manipulation of ILCs according to the target pathogen could be exploited to design more effective vaccines against chronic pathogens in the future.

Mucosal and systemic SIV-specific cytotoxic CD4+ T cell hierarchy in protection following intranasal/intramuscular recombinant pox-viral vaccination of pigtail macaques

A HIV vaccine that provides mucosal immunity is urgently needed. We evaluated an intranasal recombinant Fowlpox virus (rFPV) priming vaccine followed by intramuscular Modified Vaccinia Ankara (rMVA) booster vaccine, both expressing SIV antigens. The vaccination generated mucosal and systemic SIV-specific CD4+ T cell mediated immunity and was associated with partial protection against high-dose intrarectal SIVmac251 challenge in outbred pigtail macaques. Three of 12 vaccinees were completely protected and these animals elicited sustained Gag-specific poly-functional, cytotoxic mucosal CD4+ T cells, complemented by systemic poly-functional CD4+ and CD8+ T cell immunity. Humoral immune responses, albeit absent in completely protected macaques, were associated with partial control of viremia in animals with relatively weaker mucosal/systemic T cell responses. Co-expression of an IL-4R antagonist by the rFPV vaccine further enhanced the breadth and cytotoxicity/poly-functionality of mucosal vaccine-specific CD4+ T cells. Moreover, a single FPV-gag/pol/env prime was able to induce rapid anamnestic gp140 antibody response upon SIV encounter. Collectively, our data indicated that nasal vaccination was effective at inducing robust cervico-vaginal and rectal immunity, although cytotoxic CD4+ T cell mediated mucosal and systemic immunity correlated strongly with 'complete protection', the different degrees of protection observed was multi-factorial.

ILC2s-Trailblazers in the Host Response Against Intestinal Helminths

Group 2 innate lymphoid cells (ILC2s) were first discovered in experimental studies of intestinal helminth infection—and much of our current knowledge of ILC2 activation and function is based on the use of these models. It is perhaps not surprising therefore that these cells have also been found to play a key role in mediating protection against these large multicellular parasites. ILC2s have been intensively studied over the last decade, and are known to respond quickly and robustly to the presence of helminths—both by increasing in number and producing type 2 cytokines. These mediators function to activate and repair epithelial barriers, to recruit other innate cells such as eosinophils, and to help activate T helper 2 cells. More recent investigations have focused on the mechanisms by which the host senses helminth parasites to activate ILC2s. Such studies have identified novel stromal cell types as being involved in this process—including intestinal tuft cells and enteric neurons, which respond to the presence of helminths and activate ILC2s by producing IL-25 and Neuromedin, respectively. In the current review, we will outline the latest insights into ILC2 activation and discuss the requirement for—or redundancy of—ILC2s in providing protective immunity against intestinal helminth parasites.

Role of innate lymphoid cells and dendritic cells in intradermal immunization of the enterovirus antigen

Enterovirus type 71 (EV71) and coxsackievirus A 16 (CA16) are the major pathogens of human hand, foot, and mouth disease (HFMD). In our previous study, intramuscular immunization with the inactivated EV71 vaccine elicited effective immunity, while immunization with the inactivated CA16 vaccine did not. In this report, we focused on innate immune responses elicited by inactivated EV71 and CA16 antigens administered intradermally or intramuscularly. The distributions of the EV71 and CA16 antigens administered intradermally or intramuscularly were not obviously different, but the antigens were detected for a shorter period of time when administered intradermally. The expression levels of NF-κB pathway signaling molecules, which were identified as being capable of activating DCs, ILCs, and T cells, were higher in the intradermal group than in the intramuscular group. Antibodies for the EV71 and CA16 antigens colocalized with ILCs and DCs in skin and muscle tissues under fluorescence microscopy. Interestingly, ILC colocalization decreased over time, while DC colocalization increased over time. ELISpot analysis showed that coordination between DCs and ILCs contributed to successful adaptive immunity against vaccine antigens in the skin. EV71 and/or CA16 antigen immunization via the intradermal route was more capable of significantly increasing neutralizing antibody titers and activating specific T cell responses than immunization via the intramuscular route. Furthermore, neonatal mice born to mothers immunized with the EV71 and CA16 antigens were 100% protected against wild-type EV71 or CA16 viral challenge. Together, our results provide new insights into the development of vaccines for HFMD.

Coxsackievirus A 16 (CA16) and enterovirus 71 (EV71) infections are the most common cause of hand-foot-and-mouth diseases. Inactivated virus has been evaluated as potential vaccine for both viruses in animal models, but protection was only achieved for EV71. In this study, led by Qihan Li from the Chinese Academy of Medical Sciences, researchers show that intradermal, as compared to intramuscular immunization, results in an elevated immune response and improved protection from EV71 and CA16 infection in mice. Intradermal vaccination increases interaction of vaccine antigen with dendritic cells and innate lymphoid cells at the site of inoculation, as compared to intramuscular vaccination. Intradermal vaccination furthermore improves the antibody and T cell response and protects mice from infection. However, complete protection of mice from CA16 infection was only achieved after intradermal immunization with a combination of inactivated EV71 and CA16 vaccine, suggesting that further improvements of this vaccine candidate will be necessary.

Viral vector and route of administration determine the ILC and DC profiles responsible for downstream vaccine-specific immune outcomes

This study demonstrates that route and viral vector can significantly influence the innate lymphoid cells (ILC) and dendritic cells (DC) recruited to the vaccination site, 24 h post delivery. Intranasal (i.n.) vaccination induced ST2/IL-33R⁺ ILC2, whilst intramuscular (i.m.) induced IL-25R⁺ and TSLPR⁺ (Thymic stromal lymphopoietin protein receptor) ILC2 subsets. However, in muscle a novel ILC subset devoid of the known ILC2 markers (IL-25R^- IL-33R^- TSLPR^-) were found to express IL-13, unlike in lung. Different viral vectors also influenced the ILC-derived cytokines and the DC profiles at the respective vaccination sites. Both i.n. and i.m. recombinant fowlpox virus (rFPV) priming, which has been associated with induction of high avidity T cells and effective antibody differentiation exhibited low ILC2-derived IL-13, high NKp46⁺ ILC1/ILC3 derived IFN-γ and low IL-17A, together with enhanced CD11b⁺ CD103^- conventional DCs (cDC). In contrast, recombinant Modified Vaccinia Ankara (rMVA) and Influenza A vector priming, which has been linked to low avidity T cells, induced opposing ILC derived-cytokine profiles and enhanced cross-presenting DCs. These observations suggested that the former ILC/DC profiles could be a predictor of a balanced cellular and humoral immune outcome. In addition, following i.n. delivery Rhinovirus (RV) and Adenovius type 5 (Ad5) vectors that induced elevated ILC2-derived IL-13, NKp46⁺ ILC1/ILC3-derived-IFN-γ and no IL-17A, predominantly recruited CD11b^- B220⁺ plasmacytoid DCs (pDC). Knowing that pDC are involved in antibody differentiation, we postulate that i.n. priming with these vectors may favour induction of effective humoral immunity. Our data also revealed that vector-specific replication status and/or presence or absence of immune evasive genes can significantly alter the ILC and DC activity. Collectively, our findings suggest that understanding the route- and vector-specific ILC and DC profiles at the vaccination site may help tailor/design more efficacious viral vector-based vaccines, according to the pathogen of interest.

Innate Lymphoid Cells: A Link between the Nervous System and Microbiota in Intestinal Networks

Innate lymphoid cells (ILCs) are a novel family of innate immune cells that act as key coordinators of intestinal mucosal surface immune defense and are essential for maintaining intestinal homeostasis and barrier integrity by responding to locally produced effector cytokines or direct recognition of exogenous or endogenous danger patterns. ILCs are also involved in the pathogenesis of inflammatory bowel disease (IBD). Many studies have demonstrated the occurrence of crosstalk between ILCs and intestinal microbiota, and ILCs have recently been shown to be connected to the enteric nervous system (ENS). Thus, ILCs may act as a key link between the nervous system and microbiota in intestinal networks. In this review, we briefly summarize the role of the ILCs in the intestinal tract (particularly in the context of IBD) and discuss the relationship between ILCs and the microbiota/ENS.

Unexpected involvement of IL-13 signalling via a STAT6 independent mechanism during murine IgG2a development following viral vaccination

In this study, recombinant pox viral vaccination was shown to induce highly elevated IgG2a and low IgG1 antibody expression in mice lacking IL-4 or STAT6, whilst IL-13^-/- mice exhibited elevated IgG1, but very low IgG2a. These findings revealed that IL-13 and IL-4 differentially regulated antibody development. To understand this further, when STAT6^-/- mice were given a vaccine co-expressing IL-13Rα2 that temporarily sequestered IL-13, significantly reduced IgG2a expression, was detected. These findings for the first time demonstrated that IL-13 regulated IgG2a differentiation utilising an alternative IL-13R signalling pathway independent of STAT6 (IL-13Rα2 pathway). This was further corroborated by the (i) elevated IL-13Rα2 expression detected on STAT6^-/- lung MHCII⁺ CD11c⁺ cells 24 h post IL-13 inhibitor vaccination and ii) significant up-regulation of IL-13Rα2 expression on spleen and lung derived MHCII⁺ CD11c⁺ following inhibition of STAT6 signalling in vitro, or vaccination with IL-4R/STAT6 antagonist in vivo. When T follicular helper (Tfh) cells which regulate antibody differentiation were assessed post vaccination, although no difference in IL-4 expression was observed, greatly reduced IFN-γ expression was detected in IL-13^-/- and STAT6^-/- mice compared to wild-type. These findings support the notion that the balance of IL-13 level at the vaccination site can differentially regulate T and B-cell immune outcomes.