TLR signaling fine-tunes anti-influenza B cell responses without regulating effector T cell responses

Cytosolic nucleic acid sensing as driver of critical illness: mechanisms and advances in therapy

Nucleic acids from both self- and non-self-sources act as vital danger signals that trigger immune responses. Critical illnesses such as acute respiratory distress syndrome, sepsis, trauma and ischemia lead to the aberrant cytosolic accumulation and massive release of nucleic acids that are detected by antiviral innate immune receptors in the endosome or cytosol. Activation of receptors for deoxyribonucleic acids and ribonucleic acids triggers inflammation, a major contributor to morbidity and mortality in critically ill patients. In the past decade, there has been growing recognition of the therapeutic potential of targeting nucleic acid sensing in critical care. This review summarizes current knowledge of nucleic acid sensing in acute respiratory distress syndrome, sepsis, trauma and ischemia. Given the extensive research on nucleic acid sensing in common pathological conditions like cancer, autoimmune disorders, metabolic disorders and aging, we provide a comprehensive summary of nucleic acid sensing beyond critical illness to offer insights that may inform its role in critical conditions. Additionally, we discuss potential therapeutic strategies that specifically target nucleic acid sensing. By examining nucleic acid sources, sensor activation and function, as well as the impact of regulating these pathways across various acute diseases, we highlight the driving role of nucleic acid sensing in critical illness.

Exploring the Contribution of TLR7 to Sex-Based Disparities in Respiratory Syncytial Virus (RSV)-Induced Inflammation and Immunity

TLR7 plays a key role in recognizing viral RNA to initiate an immune response. Sex-based differences in the severity of RSV respiratory infections have been noted, and this may be related to higher expression of X-linked toll-like receptor 7 (TLR7) in female immune cells. Indeed, TLR7 has been shown to influence sex differences in responses to other respiratory viruses; however, its role in RSV infection remains underexplored. We infected adult C57Bl/6 or TLR7 knockout mice with RSV and compared the specific lung immune responses between different sexes. Gene expression analysis revealed that infected female mice had elevated levels of type I and II interferons, proinflammatory cytokines, chemokines, and viral transcripts in their lungs compared to males. Additionally, females exhibited increased numbers of macrophages and higher antibody responses in the airways. Deletion of TLR7 diminished the sex differences in certain cytokine and antibody responses. Furthermore, ex vivo infection of male alveolar macrophages with RSV resulted in greater production of proinflammatory cytokines and viral transcripts than in female macrophages, suggesting inherent sex differences in macrophage responses. These findings provide new insights into the mechanisms underlying sex differences in RSV pathophysiology and suggest that TLR7 contributes to an enhanced inflammatory response in females.

SARS-CoV-2 infection primes cross-protective respiratory IgA in a MyD88- and MAVS-dependent manner

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is constantly evolving mutations in the Spike protein to evade humoral immunity. Respiratory tract antiviral IgA antibodies are superior to circulating IgG antibodies in preventing SARS-CoV-2 infection. However, the role of innate immune signals required for the induction of mucosal IgA against SARS-CoV-2 infection is unknown. Here we show that hamsters recovered from ancestral SARS-CoV-2 infection are cross-protected against heterologous SARS-CoV-2 alpha, gamma, delta, and omicron BA.1 variants. Intranasal vaccination with an inactivated whole virus vaccine completely protects hamsters against heterologous SARS-CoV-2 infection. In addition, we show that intranasal boost vaccination of mice recovered from SARS-CoV-2 infection with unadjuvanted Spike protein induces robust levels of respiratory anti-Spike IgA and protects the mice from a heterologous SARS-CoV-2 infection. Furthermore, our findings suggest that MyD88 and MAVS play a role in the induction of the memory IgA response following an intranasal booster with unadjuvanted Spike protein in mice recovered from the SARS-CoV-2 infection. These findings provide a useful basis for the development of cross-protective mucosal vaccines against heterologous SARS-CoV-2 infection.

TLR7 Promotes Acute Inflammatory-Driven Lung Dysfunction in Influenza-Infected Mice but Prevents Late Airway Hyperresponsiveness

Severe lower respiratory tract disease following influenza A virus (IAV) infection is characterized by excessive inflammation and lung tissue damage, and this can impair lung function. The effect of toll-like receptor 7 (TLR7), which detects viral RNA to initiate antiviral and proinflammatory responses to IAV, on lung function during peak infection and in the resolution phase is not fully understood. Using wild-type (WT) C57BL/6 and TLR7 knockout (TLR7 KO) mice, we found that IAV infection induced airway dysfunction in both genotypes, although in TLR7 KO mice, this dysfunction manifested later, did not affect lung tissue elastance and damping, and was associated with a different immune phenotype. A positive correlation was found between lung dysfunction and the infiltration of neutrophils and Ly6Clo patrolling monocytes at day 7 post-infection. Conversely, in TLR7 KO mice, eosinophil and CD8+ cytotoxic T cells were associated with airway hyperactivity at day 14. IL-5 expression was higher in the airways of IAV-infected TLR7 KO mice, suggesting an enhanced Th2 response due to TLR7 deficiency. This study highlights an underappreciated duality of TLR7 in IAV disease: promoting inflammation-driven lung dysfunction during the acute infection but suppressing eosinophilic and CD8+ T cell-dependent hyperresponsiveness during disease resolution.

Comparison of Post-Vaccination Cellular Immune Response in Patients with Common Variable Immune Deficiency

BACKGROUND

The problem of identifying vaccine-specific T-cell responses is still a matter of debate. Currently, there are no universal, clearly defined, agreed upon criteria for assessing the effectiveness of vaccinations and their immunogenicity for the cellular component of immunity, even for healthy people. But for patients with inborn errors of immunity (IEI), especially those with antibody deficiencies, evaluating cellular immunity holds significant importance.

AIM

To examine the effect of one and two doses of inactivated adjuvanted subunit influenza vaccines on the expression of endosomal Toll-like receptors (TLRs) on the immune cells and the primary lymphocyte subpopulations in patients with common variable immunodeficiency (CVID).

MATERIALS AND METHODS

During 2018-2019, six CVID patients received one dose of a quadrivalent adjuvanted influenza vaccine; in 2019-2020, nine patients were vaccinated with two doses of a trivalent inactivated influenza vaccine. The proportion of key lymphocyte subpopulations and expression levels of TLRs were analyzed using flow cytometry with monoclonal antibodies.

RESULTS

No statistically significant alterations in the absolute values of the main lymphocyte subpopulations were observed in CVID patients before or after vaccination with the different immunization protocols. However, after vaccination, a higher expression of TLR3 and TLR9 in granulocytes, monocytes, and lymphocytes was found in those patients who received two vaccine doses rather than one single dose.

CONCLUSION

This study marks the first instance of using a simultaneous two-dose vaccination, which is associated with an elevated level of TLR expression in the immune cells. Administration of the adjuvanted vaccines in CVID patients appears promising. Further research into their impact on innate immunity and the development of more effective vaccination regimens is warranted.

Signaling by Type I Interferons in Immune Cells: Disease Consequences

This review addresses interferon (IFN) signaling in immune cells and the tumor microenvironment (TME) and examines how this affects cancer progression. The data reveal that IFNs exert dual roles in cancers, dependent on the TME, exhibiting both anti-tumor activity and promoting cancer progression. We discuss the abnormal IFN signaling induced by cancerous cells that alters immune responses to permit their survival and proliferation.

Control of adaptive immunity by pattern recognition receptors

One of the most significant conceptual advances in immunology in recent history is the recognition that signals from the innate immune system are required for induction of adaptive immune responses. Two breakthroughs were critical in establishing this paradigm: the identification of dendritic cells (DCs) as the cellular link between innate and adaptive immunity and the discovery of pattern recognition receptors (PRRs) as a molecular link that controls innate immune activation as well as DC function. Here, we recount the key events leading to these discoveries and discuss our current understanding of how PRRs shape adaptive immune responses, both indirectly through control of DC function and directly through control of lymphocyte function. In this context, we provide a conceptual framework for how variation in the signals generated by PRR activation, in DCs or other cell types, can influence T cell differentiation and shape the ensuing adaptive immune response.

Expression of Toll-like Receptors on the Immune Cells in Patients with Common Variable Immune Deficiency after Different Schemes of Influenza Vaccination

BACKGROUND

for the first time, the effect of one and two doses of adjuvanted influenza vaccines on toll-like receptors (TLRs) in patients with common variable immunodeficiency (CVID) was studied and compared (primary vaccination with one vs. two doses, primary vs. repeated vaccination).

MATERIALS AND METHODS

Six patients received one dose of quadrivalent adjuvanted influenza vaccine during the 2018-2019 and 2019-2020 influenza seasons, and nine patients with CVID received two doses of trivalent inactivated influenza vaccine during 2019-2020. Expression of TLRs was measured by flow cytometry.

RESULTS

The expression of toll-like receptors in patients with CVID was noted both with repeated (annual) administration of the influenza vaccine and in most cases was accompanied by an increase in the proportion of granulocytes (TLR3 and TLR9), lymphocytes (TLR3 and TLR8), and monocytes (TLR3 and TLR9). When carried out for the first time as a simultaneous vaccination with two doses it was accompanied by an increase in the proportion of granulocytes, lymphocytes expressing TLR9, and on monocytes-TLR3 and TLR9.

CONCLUSION

in CVID patients, the use of adjuvanted vaccines is promising, and research on the influence of the innate immunity and more effective regimens should be continued.

Plasmacytoid Dendritic Cells Enhance T-Independent B Cell Response through a p38 MAPK-STAT1 Axis

TLR signaling in B cells triggers their activation and differentiation independent of help from T cells. Plasmacytoid dendritic cells (pDCs) cooperate with B cells to boost TLR-stimulated T-independent humoral immunity; however, the molecular mechanisms remain elusive. In this study, we demonstrate that in the mouse system, the adjuvant effects of pDCs also occurred following challenge with pathogens and that follicular (FO) B cells were more sensitive to pDC-induced enhancement than were marginal zone (MZ) B cells. Moreover, pDCs migrated to the FO zones and interacted with FO B cells upon stimulation in vivo. CXCL10, a ligand for CXCR3 expressed on pDCs, was superinduced in the coculture system and facilitated the cooperative activation of B cells. Moreover, pDCs also promoted TLR-stimulated autoantibody production in FO B and MZ B cells. Ingenuity Pathway Analysis and gene set enrichment analysis revealed that type I IFN (IFN-I)-mediated JAK-STAT and Ras-MAPK pathways were highly enriched in R848-stimulated B cells cocultured with pDCs compared with B cells alone. Whereas IFN-I receptor 1 deficiency reduced pDC-enhanced B cell responses, STAT1 deficiency displayed a more pronounced defect. One of the STAT1-dependent but IFN-I-independent mechanisms was TLR-induced STAT1-S727 phosphorylation by p38 MAPK. Serine 727 to alanine mutation attenuated the synergism between pDCs and B cells. In conclusion, we uncover a molecular mechanism for pDC-enhanced B cell response and define a crucial role of the IFN-I/TLR-mediated signaling pathway through a p38 MAPK-STAT1 axis in controlling T-independent humoral immunity and providing a novel therapeutic target for treating autoimmune diseases.

Toll-like receptor mediated inflammation directs B cells towards protective antiviral extrafollicular responses

Extrafollicular plasmablast responses (EFRs) are considered to generate antibodies of low affinity that offer little protection from infections. Paradoxically, high avidity antigen-B cell receptor engagement is thought to be the main driver of B cell differentiation, whether in EFRs or slower-developing germinal centers (GCs). Here we show that influenza infection rapidly induces EFRs, generating protective antibodies via Toll-like receptor (TLR)-mediated mechanisms that are both B cell intrinsic and extrinsic. B cell-intrinsic TLR signals support antigen-stimulated B cell survival, clonal expansion, and the differentiation of B cells via induction of IRF4, the master regulator of B cell differentiation, through activation of NF-kB c-Rel. Provision of sustained TLR4 stimulation after immunization shifts the fate of virus-specific B cells towards EFRs instead of GCs, prompting rapid antibody production and improving their protective capacity over antigen/alum administration alone. Thus, inflammatory signals act as B cell fate-determinants for the rapid generation of protective antiviral extrafollicular responses.

A liposomal carbohydrate vaccine, adjuvanted with an NKT cell agonist, induces rapid and enhanced immune responses and antibody class switching

BACKGROUND

Congenital disorders of glycosylation (CDGs) are genetic diseases caused by gene defects in glycan biosynthesis pathways, and there is an increasing number of patients diagnosed with CDGs. Because CDGs show many different clinical symptoms, their accurate clinical diagnosis is challenging. Recently, we have shown that liposome nanoparticles bearing the ALG1-CDG and PMM2-CDG biomarkers (a tetrasaccharide: Neu5Ac-α2,6-Gal-β1,4-GlcNAc-β1,4-GlcNAc) stimulate a moderate immune response, while the generated antibodies show relatively weak affinity maturation. Thus, mature antibodies with class switching to IgG are desired to develop high-affinity antibodies that may be applied in medical applications.

RESULTS

In the present study, a liposome-based vaccine platform carrying a chemoenzymatic synthesized phytanyl-linked tetrasaccharide biomarker was optimized. The liposome nanoparticles were constructed by dioleoylphosphatidylcholine (DOPC) to improve the stability and immunogenicity of the vaccine, and adjuvanted with the NKT cell agonist PBS57 to generate high level of IgG antibodies. The results indicated that the reformulated liposomal vaccine stimulated a stronger immune response, and PBS57 successfully induce an antibody class switch to IgG. Further analyses of IgG antibodies elicited by liposome vaccines suggested their specific binding to tetrasaccharide biomarkers, which were mainly IgG2b isotypes.

CONCLUSIONS

Immunization with a liposome vaccine carrying a carbohydrate antigen and PBS57 stimulates high titers of CDG biomarker-specific IgG antibodies, thereby showing great potential as a platform to develop rapid diagnostic methods for ALG1-CDG and PMM2-CDG.

Immunopathogenesis of viral infections in neurological autoimmune disease

Autoimmune diseases develop due to self-tolerance failure in recognizing self and non-self-antigens. Several factors play a role in inducing autoimmunity, including genetic and environmental elements. Several studies demonstrated the causative role of viruses; however, some studies showed the preventive effect of viruses in the development of autoimmunity. Neurological autoimmune diseases are classified based on the targets of autoantibodies, which target intracellular or extracellular antigens rather than neurons. Several theories have been hypothesized to explain the role of viruses in the pathogenesis of neuroinflammation and autoimmune diseases. This study reviewed the current data on the immunopathogenesis of viruses in autoimmunity of the nervous system.

Transient Blockade of Type I Interferon Signalling Promotes Replication of Dengue Virus Strain D2Y98P in Adult Wild-Type Mice

Dengue virus serotypes 1 to 4 (DENV1-4) place nearly half the global population at risk of infection and the licenced tetravalent dengue vaccine fails to protect individuals who have not previously been exposed to DENV. The development of intervention strategies had long been hampered by the lack of a suitable small animal model. DENV does not replicate in wild-type mice due to its inability to antagonise the mouse type I interferon (IFN) response. Mice deficient in type I IFN signalling (Ifnar1^-/- mice) are highly susceptible to DENV infection, but their immunocompromised status makes it difficult to interpret immune responses elicited by experimental vaccines. To develop an alternative mouse model for vaccine testing, we treated adult wild-type mice with MAR1-5A3-an IFNAR1-blocking, non-cell-depleting antibody-prior to infection with the DENV2 strain D2Y98P. This approach would allow for vaccination of immunocompetent mice and subsequent inhibition of type I IFN signalling prior to challenge infection. While Ifnar1^-/- mice quickly succumbed to infection, MAR1-5A3-treated mice did not show any signs of illness but eventually seroconverted. Infectious virus was recovered from the sera and visceral organs of Ifnar1^-/- mice, but not from those of mice treated with MAR1-5A3. However, high levels of viral RNA were detected in the samples of MAR1-5A3-treated mice, indicating productive viral replication and dissemination. This transiently immunocompromised mouse model of DENV2 infection will aid the pre-clinical assessment of next-generation vaccines as well as novel antiviral treatments.

Contribution of T- and B-cell intrinsic toll-like receptors to the adaptive immune response in viral infectious diseases

Toll-like receptors (TLRs) comprise a class of highly conserved molecules that recognize pathogen-associated molecular patterns and play a vital role in host defense against multiple viral infectious diseases. Although TLRs are highly expressed on innate immune cells and play indirect roles in regulating antiviral adaptive immune responses, intrinsic expression of TLRs in adaptive immune cells, including T cells and B cells, cannot be ignored. TLRs expressed in CD4 + and CD8 + T cells play roles in enhancing TCR signal-induced T-cell activation, proliferation, function, and survival, serving as costimulatory molecules. Gene knockout of TLR signaling molecules has been shown to diminish antiviral adaptive immune responses and affect viral clearance in multiple viral infectious animal models. These results have highlighted the critical role of TLRs in the long-term immunological control of viral infection. This review summarizes the expression and function of TLR signaling pathways in T and B cells, focusing on the in vitro and vivo mechanisms and effects of intrinsic TLR signaling in regulating T- and B-cell responses during viral infection. The potential clinical use of TLR-based immune regulatory drugs for viral infectious diseases is also explored.

Female Antibodies Go the Distance against Influenza Viruses

Females have long been described to generate superior humoral immune responses relative to those in males. In the article by Ursin et al. (R. L. Ursin, S. Dhakal, H. Liu, S. Jayaraman, et al., mBio 13:e01839-22, 2022, https://doi.org/10.1128/mbio.01839-22), the authors showed that female mice generated a more robust, broadly reactive, and protective humoral immune response against influenza viruses in comparison to their male counterparts. Female mice demonstrated more efficient germinal center responses, including increased class switching and affinity maturation. Therefore, sex plays an important role in acquisition of protection against influenza viruses by modulating the generation of protective B cell responses. In this commentary, we dive into how this study builds on our understanding of how females generate superior antibody responses against influenza viruses and how this informs vaccine design.

Precision Vaccine Development: Cues From Natural Immunity

Traditional vaccine development against infectious diseases has been guided by the overarching aim to generate efficacious vaccines normally indicated by an antibody and/or cellular response that correlates with protection. However, this approach has been shown to be only a partially effective measure, since vaccine- and pathogen-specific immunity may not perfectly overlap. Thus, some vaccine development strategies, normally focused on targeted generation of both antigen specific antibody and T cell responses, resulting in a long-lived heterogenous and stable pool of memory lymphocytes, may benefit from better mimicking the immune response of a natural infection. However, challenges to achieving this goal remain unattended, due to gaps in our understanding of human immunity and full elucidation of infectious pathogenesis. In this review, we describe recent advances in the development of effective vaccines, focusing on how understanding the differences in the immunizing and non-immunizing immune responses to natural infections and corresponding shifts in immune ontogeny are crucial to inform the next generation of infectious disease vaccines.

Analysis of R848 as an Adjuvant to Improve Inactivated Influenza Vaccine Immunogenicity in Elderly Nonhuman Primates

Elderly individuals are highly susceptible to developing severe outcomes as a result of influenza A virus (IAV) infection. This can be attributed to alterations that span the aged immune system, which also result in reduced responsiveness to the seasonal inactivated vaccine. Given the rapidly increasing number of individuals in this age group, it is imperative that we develop strategies that can better protect this population from IAV-associated disease. Based on our previous findings that the TLR7/8 agonist resiquimod (R848) could efficiently boost responses in the newborn, another population with decreased vaccine responsiveness, we evaluated this adjuvant in an elderly African green monkey (AGM) model. AGM aged 16-24 years old (equivalent to 64-96 in human years) were primed and boosted with inactivated A/PuertoRico/8/1934 (H1N1) (IPR8) alone or directly linked to R848 (IPR8-R848). We observed increases in the level of circulating virus-specific IgM antibody 10 days following primary vaccination in AGM that were vaccinated with IPR8-R848, but not IPR8 alone. In addition, there were significant increases in virus-specific IgG after boosting selectively in the IPR8-R848 vaccinated animals. These findings provide insights into the ability of R848 to modulate the aged immune system in the context of IAV vaccination.

Early Post-Vaccination Gene Signatures Correlate With the Magnitude and Function of Vaccine-Induced HIV Envelope-Specific Plasma Antibodies in Infant Rhesus Macaques

A better understanding of the impact of early innate immune responses after vaccine priming on vaccine-elicited adaptive immune responses could inform rational design for effective HIV vaccines. The current study compared the whole blood molecular immune signatures of a 3M-052-SE adjuvanted HIV Env protein vaccine to a regimen combining the adjuvanted Env protein with simultaneous administration of a modified Vaccinia Ankara vector expressing HIV Env in infant rhesus macaques at days 0, 1, and 3 post vaccine prime. Both vaccines induced a rapid innate response, evident by elevated inflammatory plasma cytokines and altered gene expression. We identified 25 differentially-expressed genes (DEG) on day 1 compared to day 0 in the HIV protein vaccine group. In contrast, in the group that received both the Env protein and the MVA-Env vaccine only two DEG were identified, implying that the MVA-Env modified the innate response to the adjuvanted protein vaccine. By day 3, only three DEG maintained altered expression, indicative of the transient nature of the innate response. The DEG represented immune pathways associated with complement activation, type I interferon and interleukin signaling, pathogen sensing, and induction of adaptive immunity. DEG expression on day 1 was correlated to Env-specific antibody responses, in particular antibody-dependent cytotoxicity responses at week 34, and Env-specific follicular T helper cells. Results from network analysis supported the interaction of DEG and their proteins in B cell activation. These results emphasize that vaccine-induced HIV-specific antibody responses can be optimized through the modulation of the innate response to the vaccine prime.

Influenza Viruses: Innate Immunity and mRNA Vaccines

The innate immune system represents the first line of defense against influenza viruses, which cause severe inflammation of the respiratory tract and are responsible for more than 650,000 deaths annually worldwide. mRNA vaccines are promising alternatives to traditional vaccine approaches due to their safe dosing, low-cost manufacturing, rapid development capability, and high efficacy. In this review, we provide our current understanding of the innate immune response that uses pattern recognition receptors to detect and respond to mRNA vaccination. We also provide an overview of mRNA vaccines, and discuss the future directions and challenges in advancing this promising therapeutic approach.

Immunomodulation by the Commensal Microbiome During Immune-Targeted Interventions: Focus on Cancer Immune Checkpoint Inhibitor Therapy and Vaccination

Emerging evidence in clinical and preclinical studies indicates that success of immunotherapies can be impacted by the state of the microbiome. Understanding the role of the microbiome during immune-targeted interventions could help us understand heterogeneity of treatment success, predict outcomes, and develop additional strategies to improve efficacy. In this review, we discuss key studies that reveal reciprocal interactions between the microbiome, the immune system, and the outcome of immune interventions. We focus on cancer immune checkpoint inhibitor treatment and vaccination as two crucial therapeutic areas with strong potential for immunomodulation by the microbiota. By juxtaposing studies across both therapeutic areas, we highlight three factors prominently involved in microbial immunomodulation: short-chain fatty acids, microbe-associate molecular patterns (MAMPs), and inflammatory cytokines. Continued interrogation of these models and pathways may reveal critical mechanistic synergies between the microbiome and the immune system, resulting in novel approaches designed to influence the efficacy of immune-targeted interventions.

TLR7 Is Critical for Anti-Viral Humoral Immunity to EV71 Infection in the Spinal Cord

Enterovirus 71 (EV71) is a positive single-stranded RNA (ssRNA) virus from the enterovirus genus of Picornaviridae family and causes diseases ranged from the mild disease of hand, foot and mouth disease (HFMD) to the severe disease of neurological involvement in young children. TLR7 is an intracellular pattern recognition receptor (PRR) recognizing viral ssRNA. In this study, we investigated the role of TLR7 in EV71 infection in mouse pups (10-12 days old) and found that wild-type (WT) and TLR7 knock-out (TLR7KO) mice infected with EV71 showed similar limb paralysis at the onset and peak of the disease, comparable loss of motor neurons, and similar levels of antiviral molecules in the spinal cord. These results suggest that TLR7 is not the absolute PRR for EV71 in the spinal cord. Interestingly, TLR7KO mice infected with EV71 exhibited significantly delayed recovery from limb paralysis compared with WT mice. TLR7KO mice infected with EV71 showed significantly decreased levels of IgM and IgG2, important antibodies for antiviral humoral immunity. Furthermore, TLR7KO mice infected with EV71 showed a decrease of germinal center B cells in the spleen compared with WT mice. Altogether, our study suggests that TLR7 plays a critical role in anti-viral humoral immunity rather than in being a PRR in the spinal cord during EV71 infection in young mice.

Defective Toll-Like Receptors Driven B Cell Response in Hyper IgE Syndrome Patients With STAT3 Mutations

Autosomal dominant hyper-IgE syndrome (AD-HIES) is a rare inherited primary immunodeficient disease (PIDs), which is caused by STAT3 gene mutations. Previous studies indicated a defective Toll-like receptor (TLR) 9-induced B cell response in AD-HIES patients, including proliferation, and IgG production. However, the other TLRs-mediated B cell responses in AD-HIES patients were not fully elucidated. In this study, we systematically studied the B cell response to TLRs signaling pathways in AD-HIES patients, including proliferation, activation, apoptosis, cytokine, and immunoglobulin production. Our results showed that the TLRs-induced B cell proliferation and activation was significantly impaired in AD-HIES patients. Besides, AD-HIES patients had defects in TLRs-induced B cell class switch, as well as IgG/IgM secretion and IL-10 production in B cells. Taken together, we first systematically reported the deficiency of TLRs driven B cell response in AD-HIES patients, which help to have a better understanding of the pathology of AD-HIES.

NF-κB signaling induces inductive expression of the downstream molecules and IgD gene in the freshwater carp, Catla catla

Toll-like receptors (TLRs) in innate immune system act as primary sensors in detecting the microbial components and activate their signaling cascades to induce NF-κB (nuclear factor NF-κB) towards the augmentation of immunoglobulin (Ig) synthesis. To gain insights into the efficacy of NF-κB pathway in immunoglobulin D (IgD) synthesis in the Indian Major Carp Catla catla, cloning and sequencing of TLR-signaling downstream molecules [TRAF3 (TNF receptor-associated factor 3), NEMO (nuclear factor-kappa B essential modulator), NF-κB and BAFF (B cell activating factor)] were performed by infecting the fish with pathogens. mRNA expression analysis of the downstream molecules and IgD showed significant up-regulation of these genes in kidney (P ≤ 0.001) as compared to spleen (P ≤ 0.05). To ascertain the role of NF-κB pathway in IgD synthesis, the primary cell culture of kidney and spleen in monolayer cell suspension was treated with NF-κB inhibitor (BAY 11-7082) and down-regulation of BAFF, NEMO, NF-κB, and IgD gene was observed. These results highlight the importance of NF-κB signaling pathway in augmenting the IgD gene expression in the freshwater carp, Catla catla.

Influenza-Host Interplay and Strategies for Universal Vaccine Development

Influenza is an annual epidemic and an occasional pandemic caused by pathogens that are responsible for infectious respiratory disease. Humans are highly susceptible to the infection mediated by influenza A viruses (IAV). The entry of the virus is mediated by the influenza virus hemagglutinin (HA) glycoprotein that binds to the cellular sialic acid receptors and facilitates the fusion of the viral membrane with the endosomal membrane. During IAV infection, virus-derived pathogen-associated molecular patterns (PAMPs) are recognized by host intracellular specific sensors including toll-like receptors (TLRs), C-type lectin receptors, retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), and nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) either on the cell surface or intracellularly in endosomes. Herein, we comprehensively review the current knowledge available on the entry of the influenza virus into host cells and the molecular details of the influenza virus–host interface. We also highlight certain strategies for the development of universal influenza vaccines.

Host Protective Immune Responses against Influenza A Virus Infection

Influenza viruses cause infectious respiratory disease characterized by fever, myalgia, and congestion, ranging in severity from mild to life-threating. Although enormous efforts have aimed to prevent and treat influenza infections, seasonal and pandemic influenza outbreaks remain a major public health concern. This is largely because influenza viruses rapidly undergo genetic mutations that restrict the long-lasting efficacy of vaccine-induced immune responses and therapeutic regimens. In this review, we discuss the virological features of influenza A viruses and provide an overview of current knowledge of the innate sensing of invading influenza viruses and the protective immune responses in the host.

The Clinical Presentation and Immunology of Viral Pneumonia and Implications for Management of Coronavirus Disease 2019

This review will briefly examine the clinical presentation and important immunology of viral pneumonia with a focus on severe acute respiratory syndrome coronavirus 2 (coronavirus disease 2019).

Metformin-induced suppression of IFN-α via mTORC1 signalling following seasonal vaccination is associated with impaired antibody responses in type 2 diabetes

Diabetes mellitus (DM) patients are at an increased risk of complications following influenza-virus infection, seasonal vaccination (SV) is recommended. However, SV with trivalent influenza vaccine (TIV) can induce antibody and type-I interferon (IFN) responses, and the effect of anti-DM treatment on these responses is incompletely understood. We evaluated the antibody response and IFN-α expression in individuals with and without type 2 DM (T2DM) following SV, and examined the effects on anti-DM treatment. TIV elicited sero-protection in all groups, but antibody persistency was <8 months, except for the antibody response to B-antigens in non-DM. T2DM impaired the IgG avidity index, and T2DM showed a significantly decreased response against H1N1 and H3N2, in addition to delaying and reducing haemagglutination-inhibition persistency against influenza B-antigens in DM groups treated with metformin (Met-DM) or glibenclamide (GB-DM). Following TIV, the Met-DM and GB-DM groups exhibited reduced IFN-α expression upon stimulation with whole- and split-virion influenza vaccines. Suppression of IFN-α expression in the Met-DM group was associated with a reduction in the mechanistic target of rapamycin complex-1 pathway and impaired IgG avidity index. Thus, single-dose TIV each year might not be suitable for T2DM. Our data could aid the development of an efficacious influenza vaccine for T2DM.

How the Respiratory Epithelium Senses and Reacts to Influenza Virus

The human lung is constantly exposed to the environment and potential pathogens. As the interface between host and environment, the respiratory epithelium has evolved sophisticated sensing mechanisms as part of its defense against pathogens. In this review, we examine how the respiratory epithelium senses and responds to influenza A virus, the biggest cause of respiratory viral deaths worldwide.

TLRs in pulmonary diseases

Toll-like receptors (TLRs) comprise a clan of proteins involved in identification and triggering a suitable response against pathogenic attacks. As lung is steadily exposed to multiple infectious agents, antigens and host-derived danger signals, the inhabiting stromal and myeloid cells of the lung express an aggregate of TLRs which perceive the endogenously derived damage-associated molecular patterns (DAMPs) along with pathogen associated molecular patterns (PAMPs) and trigger the TLR-associated signalling events involved in host defence. Thus, they form an imperative component of host defence activation in case of microbial infections as well as non-infectious pulmonary disorders such as interstitial lung disease, acute lung injury and airways disease, such as COPD and asthma. They also play an equally important role in lung cancer. Targeting the TLR signalling network would pave ways to the design of more reliable and effective vaccines against infectious agents and control deadly infections, desensitize allergens and reduce inflammation. Moreover, TLR agonists may act as adjuvants by increasing the efficiency of cancer vaccines, thereby contributing their role in treatment of lung cancer too. Overall, TLRs present a compelling and expeditiously bolstered area of research and addressing their signalling events would be of significant use in pulmonary diseases.

The dual role of innate immunity during influenza

One of the distinguishing features of the 1918 pandemic is the occurrence of massive, potentially detrimental, activation of the innate immune system in critically ill patients. Whether this reflects an intrinsic capacity of the virus to induce an exaggerated inflammatory responses or its remarkable ability to reproduce in vivo is still open to debate. Tremendous progress has recently been made in our understanding of innate immune responses to influenza infection and it is now time to translate this knowledge into therapeutic strategies, particularly in view of the possible occurrence of future outbreaks caused by virulent strains.

Toll-Like Receptor 7 Enhances Rabies Virus-Induced Humoral Immunity by Facilitating the Formation of Germinal Centers

Rabies virus (RABV) causes fatal encephalitis in mammals and poses a public health threat in many parts of the world. Vaccination remains the most effective means for prevention and control of rabies. Studies focusing on the mechanism of RABV immunogenicity are necessary for improvement of rabies vaccines. Toll-like receptor 7 (TLR7), an innate receptor sensing single-stranded viral RNA, is important for the induction of innate and adaptive immunity. Our studies revealed that the absence of TLR7 led to a lower antibody production in mice immunized with RABV. It is further found that TLR7 deficiency affected the recruitment of germinal center (GC) B cells and led to lessened GCs formation. Consistently, there were less plasma cells (PCs) and antibody secreting cells (ASC) in TLR7^-/- mice than those in wild type (WT) mice, resulting in impaired production of RABV-neutralizing antibodies (VNA). TLR7 deficiency also impaired the generation of memory B cells (MBCs) and the induction of secondary immune responses. Moreover, TLR7 deficiency down-regulated the induction of some cytokines/chemokines, especially IFN-γ, resulting in a Th2-biased antibody production. Overall, our results suggest that TLR7 facilitates the induction of the humoral immunity in response to RABV.

Single Cell Profiling Reveals PTEN Overexpression in Influenza-Specific B cells in Aging HIV-infected individuals on Anti-retroviral Therapy

Memory B cells (MBC) respond to secondary antigen challenge to protect against infection and to boost immunity following vaccinations. Despite effective treatment, chronic HIV infection disturbs MBCs by reducing numbers and altering functionality due to hyper-activation and increased apoptosis leading to suboptimal antibody responses against common infectious agents. We used single cell gene expression analysis to evaluate antigen-specific memory B cells in peripheral blood of virally-suppressed HIV-infected individuals and healthy controls stratified by serum H1N1 antibody response 3 weeks post-administration of the seasonal trivalent inactivated influenza vaccine. We used a fluorescent probe to isolate influenza H1N1-specific B cells and a multiplexed and targeted RT-PCR approach to measure expression levels of 96 genes involved in B cell activation and function. Gene profiling revealed a 4-gene predictive signature containing the phosphoinositide-3 kinase (PI3K) inhibitor, PTEN, for identifying antigen-specific MBC from HIV-infected individuals compared to healthy controls. Gene co-expression analysis showed that in addition to overexpression of PTEN, there was increased co-expression of type I interferon-associated genes with PTEN on single cell level in HIV compared to controls. This study highlights the persistent defects in MBC from HIV-infected individuals and points to the PI3K signaling pathway as a target for potential immune intervention.

The Multifaceted B Cell Response to Influenza Virus

Protection from yearly recurring, highly acute infections with a pathogen that rapidly and continuously evades previously induced protective neutralizing Abs, as seen during seasonal influenza virus infections, can be expected to require a B cell response that is too highly variable, able to adapt rapidly, and able to reduce morbidity and death when sterile immunity cannot be garnered quickly enough. As we outline in this Brief Review, the influenza-specific B cell response is exactly that: it is multifaceted, involves both innate-like and conventional B cells, provides early and later immune protection, employs B cells with distinct BCR repertoires and distinct modes of activation, and continuously adapts to the ever-changing virus while enhancing overall protection. A formidable response to a formidable pathogen.

The choice of linker for conjugating R848 to inactivated influenza virus determines the stimulatory capacity for innate immune cells

Inactivated influenza vaccines are not approved for use in infants less than 6 months of age due to poor immunogenicity in that population. While the live attenuated influenza vaccine has the potential to be more immunogenic, it is not an option for infants and other vulnerable populations, including the elderly and immunocompromised individuals due to safety concerns. In an effort to improve the immunogenicity of the inactivated vaccine for use in vulnerable populations, we have used an approach of chemically crosslinking the Toll-like receptor (TLR) 7/8 agonist R848 directly to virus particles. We have reported previously that an R848-conjugated, inactivated vaccine is more effective at inducing adaptive immune responses and protecting against lung pathology in influenza challenged neonatal African green monkeys than is the unmodified counterpart. In the current study, we describe a second generation vaccine that utilizes an amide-sulfhydryl crosslinker with different spacer chemistry and length to couple R848 to virions. The new vaccine has significantly enhanced immunostimulatory activity for murine macrophages and importantly for monocyte derived human dendritic cells. Demonstration of the significant differences in stimulatory activity afforded by modest changes in linker impacts our fundamental view of the design of TLR agonist-antigen vaccines.

The role of respiratory epithelium in host defence against influenza virus infection

The respiratory epithelium is the major interface between the environment and the host. Sophisticated barrier, sensing, anti-microbial and immune regulatory mechanisms have evolved to help maintain homeostasis and to defend the lung against foreign substances and pathogens. During influenza virus infection, these specialised structural cells and populations of resident immune cells come together to mount the first response to the virus, one which would play a significant role in the immediate and long term outcome of the infection. In this review, we focus on the immune defence machinery of the respiratory epithelium and briefly explore how it repairs and regenerates after infection.

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.

Galectin-9 inhibits TLR7-mediated autoimmunity in murine lupus models

Uncontrolled secretion of type I IFN, as the result of endosomal TLR (i.e., TLR7 and TLR9) signaling in plasmacytoid DCs (pDCs), and abnormal production of autoantibodies by B cells are critical for systemic lupus erythematosus (SLE) pathogenesis. The importance of galectin-9 (Gal-9) in regulating various autoimmune diseases, including lupus, has been demonstrated. However, the precise mechanism by which Gal-9 mediates this effect remains unclear. Here, using spontaneous murine models of lupus (i.e., BXSB/MpJ and NZB/W F1 mice), we demonstrate that administration of Gal-9 results in reduced TLR7-mediated autoimmune manifestations. While investigating the mechanism underlying this phenomenon, we observed that Gal-9 inhibits the phenotypic maturation of pDCs and B cells and abrogates their ability to mount cytokine responses to TLR7/TLR9 ligands. Importantly, immunocomplex-mediated (IC-mediated) and neutrophil extracellular trap-mediated (NET-mediated) pDC activation was inhibited by Gal-9. Additionally, the mTOR/p70S6K pathway, which is recruited by both pDCs and B cells for TLR-mediated IFN secretion and autoantibody generation, respectively, was attenuated. Gal-9 was found to exert its inhibitory effect on both the cells by interacting with CD44.

Induction and Subversion of Human Protective Immunity: Contrasting Influenza and Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) and influenza are among the most important causes of severe respiratory disease worldwide. Despite the clinical need, barriers to developing reliably effective vaccines against these viruses have remained firmly in place for decades. Overcoming these hurdles requires better understanding of human immunity and the strategies by which these pathogens evade it. Although superficially similar, the virology and host response to RSV and influenza are strikingly distinct. Influenza induces robust strain-specific immunity following natural infection, although protection by current vaccines is short-lived. In contrast, even strain-specific protection is incomplete after RSV and there are currently no licensed RSV vaccines. Although animal models have been critical for developing a fundamental understanding of antiviral immunity, extrapolating to human disease has been problematic. It is only with recent translational advances (such as controlled human infection models and high-dimensional technologies) that the mechanisms responsible for differences in protection against RSV compared to influenza have begun to be elucidated in the human context. Influenza infection elicits high-affinity IgA in the respiratory tract and virus-specific IgG, which correlates with protection. Long-lived influenza-specific T cells have also been shown to ameliorate disease. This robust immunity promotes rapid emergence of antigenic variants leading to immune escape. RSV differs markedly, as reinfection with similar strains occurs despite natural infection inducing high levels of antibody against conserved antigens. The immunomodulatory mechanisms of RSV are thus highly effective in inhibiting long-term protection, with disturbance of type I interferon signaling, antigen presentation and chemokine-induced inflammation possibly all contributing. These lead to widespread effects on adaptive immunity with impaired B cell memory and reduced T cell generation and functionality. Here, we discuss the differences in clinical outcome and immune response following influenza and RSV. Specifically, we focus on differences in their recognition by innate immunity; the strategies used by each virus to evade these early immune responses; and effects across the innate-adaptive interface that may prevent long-lived memory generation. Thus, by comparing these globally important pathogens, we highlight mechanisms by which optimal antiviral immunity may be better induced and discuss the potential for these insights to inform novel vaccines.

Sex bias in mouse humoral immune response to influenza vaccine depends on the vaccine type

The study explored influence of biological sex on development of humoral immune response to seasonal trivalent whole inactivated virus (WIV) and split virus (SV) influenza vaccines in outbred Swiss mouse model. To this end, mice of both sexes were immunized with WIV (WIV mice) and SV vaccines (SV mice) and examined for specific antibody response. Irrespective of sex, total IgG and neutralizing antibody responses to distinct virus strains were weaker in SV than in WIV mice. In WIV mice of both sexes, irrespective of strain specificity, IgG isotype response was dominated by IgG2a antibodies, while in SV mice nearly equal representation of IgG2a and IgG1 antibodies was found. The analyses of sex differences showed higher titers of H1N1-specific and both H1N1- and H3N2-specific total IgG and neutralizing antibodies in female WIV and SV mice, respectively. Additionally, sexual dimorphism in IgG subclass profile depended on vaccine type. Specifically, compared with males, in females WIV shifted IgG2a/IgG1 antibody ratio towards IgG2a isotype on the account of weaker IgG1 response, whereas in SV mice, irrespective of virus strain, IgG2a and IgG1 isotypes were equally represented in both sexes. These findings indicate the vaccine type-dependent sex bias in antibody response to inactivated influenza vaccines.

Respiratory Influenza A Virus Infection Triggers Local and Systemic Natural Killer Cell Activation via Toll-Like Receptor 7

The innate immune system senses influenza A virus (IAV) through different pathogen-recognition receptors including Toll-like receptor 7 (TLR7). Downstream of viral recognition natural killer (NK) cells are activated as part of the anti-IAV immune response. Despite the known decisive role of TLR7 for NK cell activation by therapeutic immunostimulatory RNAs, the contribution of TLR7 to the NK cell response following IAV infection has not been addressed. We have analyzed lung cytokine responses as well as the activation, interferon (IFN)-γ production, and cytotoxicity of lung and splenic NK cells following sublethal respiratory IAV infection in wild-type and TLR7ko mice. Early airway IFN-γ levels as well as the induction of lung NK cell CD69 expression and IFN-γ production in response to IAV infection were significantly attenuated in TLR7-deficient hosts. Strikingly, respiratory IAV infection also primed splenic NK cells for IFN-γ production, degranulation, and target cell lysis, all of which were fully dependent on TLR7. At the same time, lung type I IFN levels were significantly reduced in TLR7ko mice early following IAV infection, displaying a potential upstream mechanism of the attenuated NK cell activation observed. Taken together, our data clearly demonstrate a specific role for TLR7 signaling in local and systemic NK cell activation following respiratory IAV infection despite the presence of redundant innate IAV-recognition pathways.

Humoral Responses Elicited by Adenovirus Displaying Epitopes Are Induced Independently of the Infection Process and Shaped by the Toll-Like Receptor/MyD88 Pathway

The use of serotype 5 adenovirus (Ad)-derived vectors in vaccination is confronted to preexisting anti-Ad immunity. Epitope display on Ad capsid is currently being investigated as an alternative approach of vaccination. The present study seeks to better understand virus- and host-related factors controlling the efficacy of this new vaccination approach. In contrast to an Ad vector expressing ovalbumin as a transgene, Ad displaying an ovalbumin-derived B-cell epitope inserted into the fiber protein was able to elicit antibody responses in both Ad-naive and Ad-immune mice. Moreover, introduction of a set of mutations abrogating Ad interaction with its receptors did not modify the virus capacity to elicit a humoral response against the inserted epitope while reducing its capacity to mount antibody responses against the transgene product. Taken as a whole these data indicate that the efficacy of Ad displaying epitopes requires neither Ad binding to its receptors nor the infection process. In addition, the use of genetically deficient mice demonstrated that both toll-like receptor (TLR)/MyD88 and RIG-I/mitochondrial antiviral-signaling (MAVS) innate immunity pathways were dispensable to mount anti-epitope antibody responses. However, they also revealed that TLR/MyD88 pathway but not RIG-I/MAVS pathway controls the nature of antibodies directed against the displayed epitope.

Co-Stimulation of BCR and Toll-Like Receptor 7 Increases Somatic Hypermutation, Memory B Cell Formation, and Secondary Antibody Response to Protein Antigen

The goal of immunization is to produce both a flood of antibodies to neutralize antigen and memory cells to accelerate the secondary response. To enhance the generation of memory B cells, we examined the effect of co-engaging BCR and toll-like receptor (TLR) 7 receptors by immunizing mice with a hapten-protein antigen, NP-CGG, and a ligand, R837 (imiquimod). During the early and late primary responses, there was no augmentation with R837 on the number of germinal center B cells or serum antibody. However, in the niche of germinal centers, R837 increased somatic hypermutation in the canonical V_H1-72 gene that encodes NP-specific antibody. Increased mutation was not due to enhanced expression of activation-induced deaminase, but was likely a result of selection for high-affinity B cells with altered codons in the gene. This correlated with the appearance of antigen-specific B cells with a memory phenotype, which was intrinsic to TLR7 on B cells. To determine if these memory cells produced a recall response after a secondary challenge, spleen cells from mice that were immunized with NP-CGG and R837 were adoptively transferred into muMT recipients, and boosted with NP-CGG. Cells from mice that initially received both antigen and R837 generated a robust increase in germinal center B cells, plasmablasts, plasma cells, and serum antibody, compared with their cohorts who received antigen alone. These results support the use of co-immunization with TLR7 ligands to promote vigorous memory B cell responses to protein antigens.

Distinct Effects of Monophosphoryl Lipid A, Oligodeoxynucleotide CpG, and Combination Adjuvants on Modulating Innate and Adaptive Immune Responses to Influenza Vaccination

Monophosphoryl lipid A (MPL) and oligodeoxynucleotide CpG are toll-like receptor (TLR) 4 and 9 agonist, respectively. Here, we investigated the effects of MPL, CpG, and combination adjuvants on stimulating in vitro dendritic cells (DCs), in vivo innate and adaptive immune responses, and protective efficacy of influenza vaccination. Combination of MPL and CpG was found to exhibit distinct effects on stimulating DCs in vitro to secrete IL-12p70 and tumor necrosis factor (TNF)-α and proliferate allogeneic CD8 T cells. Prime immunization of mice with inactivated split influenza vaccine in the presence of low dose MPL+CpG adjuvants increased the induction of virus-specific IgG and IgG2a isotype antibodies. MPL and CpG adjuvants contribute to improving the efficacy of prime influenza vaccination against lethal influenza challenge as determined by body weight monitoring, lung function, viral titers, and histology. A combination of MPL and CpG adjuvants was effective in improving vaccine efficacy as well as in reducing inflammatory immune responses locally and in inducing cellular immune responses upon lethal influenza virus challenge. This study demonstrates unique adjuvant effects of MPL, CpG, and combination adjuvants on modulating innate and adaptive immune responses to influenza prime vaccination.

Immunologic response to vaccine challenge in pregnant PTPN22 R620W carriers and non-carriers

Objectives

Influenza infection is a significant cause of respiratory morbidity among pregnant women. Seasonal influenza vaccination engages innate immune receptors to promote protective immunity. A coding polymorphism (R620W) in PTPN22 imparts elevated risk for human infection and autoimmune disease, predisposes to diminished innate immune responses, and associates with reduced immunization responses. We sought to quantify the effects of PTPN22-R620W on humoral and cell-mediated immune responses to the inactivated influenza vaccine among healthy pregnant women.

Study Design

Immune responses were measured in healthy pregnant R620W carrier (n = 17) and non-carrier (n = 33) women receiving the 2013 quadrivalent inactivated influenza vaccine (Fluzone). Hemagglutination inhibition assays were performed to quantify neutralizing antibodies; functional influenza-reactive CD4 T cells were quantified by flow cytometry, and influenza-specific CD8 T cells were enumerated with MHC Class I tetramers. Antibody seroconversion data were evaluated by Chi-square analysis, and the Mann-Whitney or Wilcoxon signed-rank tests were applied to T cell response data.

Results

PTPN22 R620W carrier (n = 17) and non-carrier (n = 33) groups did not differ in age, parity, BMI, gestational age at time of vaccine, or history of prior influenza vaccination. After Fluzone exposure, 51.5% of non-carriers met criteria for antibody seroconversion to H1N1 influenza, compared with 23.5% of R620W carriers (p = 0.06). Influenza-reactive CD4 T cells showed modest increase at days 9–15 after vaccination in both R620W carriers and non-carriers (p = 0.02 and p = 0.04, respectively). However, there was no difference in overall response between the two groups (p = 0.6). The vaccine did not result in significant induction of influenza-specific CD8 T cells in either group.

Conclusions

There was no significant difference among healthy pregnant R620W carriers and non-carriers in H1N1 antibody seroconversion rates after influenza vaccination. Studies of larger cohorts will be needed to define the effect of PTPN22 risk allele carriage on antibody and T cell responses to influenza vaccination during pregnancy.

Combination of poly I:C and Pam3CSK4 enhances activation of B cells in vitro and boosts antibody responses to protein vaccines in vivo

Vaccines that can rapidly induce strong and robust antibody-mediated immunity could improve protection from certain infectious diseases for which current vaccine formulations are inefficient. For indications such as anthrax and influenza, antibody production in vivo is a correlate of efficacy. Toll-like receptor (TLR) agonists are frequently studied for their role as vaccine adjuvants, largely because of their ability to enhance initiation of immune responses to antigens by activating dendritic cells. However, TLRs are also expressed on B cells and may contribute to effective B cell activation and promote differentiation into antigen-specific antibody producing plasma cells in vivo. We sought to discover an adjuvant system that could be used to augment antibody responses to influenza and anthrax vaccines. We first characterized an adjuvant system in vitro which consisted of two TLR ligands, poly I:C (TLR3) and Pam3CSK4 (TLR2), by evaluating its effects on B cell activation. Each agonist enhanced B cell activation through increased expression of surface receptors, cytokine secretion and proliferation. However, when B cells were stimulated with poly I:C and Pam3CSK4 in combination, further enhancement to cell activation was observed. Using B cells isolated from knockout mice we confirmed that poly I:C and Pam3CSK4 were signaling through TLR3 and TLR2, respectively. B cells activated with Poly I:C and Pam3CSK4 displayed enhanced capacity to stimulate allogeneic CD4⁺ T cell activation and differentiate into antibody-producing plasma cells in vitro. Mice vaccinated with influenza or anthrax antigens formulated with poly I:C and Pam3CSK4 in DepoVax^™ vaccine platform developed a rapid and strong antigen-specific serum antibody titer that persisted for at least 12 weeks after a single immunization. These results demonstrate that combinations of TLR adjuvants promote more effective B cell activation in vitro and can be used to augment antibody responses to vaccines in vivo.

Recognition of Viral RNA by Pattern Recognition Receptors in the Induction of Innate Immunity and Excessive Inflammation During Respiratory Viral Infections

The innate immune system is the first line of defense against virus infection that triggers the expression of type I interferon (IFN) and proinflammatory cytokines. Pattern recognition receptors (PRRs) recognize pathogen-associated molecular patterns, resulting in the induction of innate immune responses. Viral RNA in endosomes is recognized by Toll-like receptors, and cytoplasmic viral RNA is recognized by RIG-I-like receptors. The host innate immune response is critical for protection against virus infection. However, it has been postulated that an excessive inflammatory response in the lung caused by the innate immune response is harmful to the host and is a cause of lethality during influenza A virus infection. Although the deletion of genes encoding PRRs or proinflammatory cytokines does not improve the mortality of mice infected with influenza A virus, a partial block of the innate immune response is successful in decreasing the mortality rate of mice without a loss of protection against virus infection. In addition, morbidity and mortality rates are influenced by other factors. For example, secondary bacterial infection increases the mortality rate in patients with influenza A virus and in animal models of the disease, and environmental factors, such as cigarette smoke and fine particles, also affect the innate immune response. In this review, we summarize recent findings related to the role of PRRs in innate immune response during respiratory viral infection.

Interactions Between NS1 of Influenza A Viruses and Interferon-α/β: Determinants for Vaccine Development

Influenza A viruses (IAVs) cause mild to severe infections in humans with considerable socioeconomic and global health consequences. The host interferon (IFN)-α/β response, critical as the first line of defense against foreign pathogens, is induced upon detection of IAV genomic RNA in infected cells by host innate pattern recognition receptors. IFN-α/β production and subsequent activation of cell signaling result in the expression of antiviral IFN-stimulated genes whose products target various stages of the IAV life cycle to inhibit viral replication and the spread of infection and establish an antiviral state. IAVs, however, encode a multifunctional virulence factor, nonstructural protein 1 (NS1), that directly antagonizes the host IFN-α/β response to support viral replication. In this review, we highlight the mechanisms by which NS1 suppresses IFN-α/β production and subsequent cell signaling, and consider, therefore, the potential for recombinant IAVs lacking NS1 to be used as live-attenuated vaccines.

The viral innate immune antagonism and an alternative vaccine design for PRRS virus

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PRRS virus has evolved to suppress the antiviral innate immunity during infection.

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Type I interferons are potent antiviral cytokines and function to stimulate the adaptive immune responses.

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Six viral proteins have been identified as interferon antagonists and characterized for their molecular actions.

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Interferon antagonism-negative viruses are attenuated and have been proven induce protective immunity.

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Interferon suppression-negative PRRS virus may serve as an alternative vaccine for PRRS.

Porcine reproductive and respiratory syndrome (PRRS) remains one of the most economically significant diseases in the swine industry worldwide. The current vaccines are less satisfactory to confer protections from heterologous infections and long-term persistence, and the need for better vaccines are urgent. The immunological hallmarks in PRRSV-infected pigs include the unusually poor production of type I interferons (IFNs-α/β) and the aberrant and delayed adaptive immune responses, indicating that PRRSV has the ability to suppress both innate and adaptive immune responses in the host. Type I IFNs are the potent antiviral cytokines and recent studies reveal their pleiotropic functions in the priming of expansion and maturation of adaptive immunity. Thus, IFN antagonism-negative PRRSV is hypothesized to be attenuated and to build effective and broad- spectrum innate and adaptive immune responses in pigs. Such vaccines are promising alternatives to traditional vaccines for PRRSV.

Consecutive inoculations of influenza virus vaccine and poly(I:C) protects mice against homologous and heterologous virus challenge

Mucosal immunity induced through natural infection by influenza virus has potent cross-protective activity, compared to subcutaneous vaccination-induced systemic immunity. Compared to natural infection with influenza virus, however, a single intranasal vaccination with an inactivated influenza virus vaccine and poly(I:C) is not sufficient to induce primary immune response in naïve animals. The reasons for this moderate effect are not fully understood. Here, we demonstrated that intranasal vaccination with formalin-inactivated influenza virus vaccine and poly(I:C) for five consecutive days elicits high levels of virus-specific nasal IgA and serum IgG responses, while vaccination without poly(I:C) induced little response. Mice immunized with influenza virus vaccine and poly(I:C) for five consecutive days sustained high levels of virus-specific IgA in nasal wash and IgG in serum until at least 6months after vaccination. Furthermore, intranasal vaccination with influenza virus vaccine and poly(I:C) protected mice against homologous and heterologous influenza virus challenge. These results suggest that consecutive inoculations of influenza virus vaccine and poly(I:C) is an alternative method to induce primary immune responses in naïve subjects.

The Ebola Interferon Inhibiting Domains Attenuate and Dysregulate Cell-Mediated Immune Responses

Ebola virus (EBOV) infections are characterized by deficient T-lymphocyte responses, T-lymphocyte apoptosis and lymphopenia. We previously showed that disabling of interferon-inhibiting domains (IIDs) in the VP24 and VP35 proteins effectively unblocks maturation of dendritic cells (DCs) and increases the secretion of cytokines and chemokines. Here, we investigated the role of IIDs in adaptive and innate cell-mediated responses using recombinant viruses carrying point mutations, which disabled IIDs in VP24 (EBOV/VP24m), VP35 (EBOV/VP35m) or both (EBOV/VP35m/VP24m). Peripheral blood mononuclear cells (PBMCs) from cytomegalovirus (CMV)-seropositive donors were inoculated with the panel of viruses and stimulated with CMV pp65 peptides. Disabling of the VP35 IID resulted in increased proliferation and higher percentages of CD4+ T cells secreting IFNγ and/or TNFα. To address the role of aberrant DC maturation in the IID-mediated suppression of T cell responses, CMV-stimulated DCs were infected with the panel of viruses and co-cultured with autologous T-lymphocytes. Infection with EBOV/VP35m infection resulted in a significant increase, as compared to wt EBOV, in proliferating CD4+ cells secreting IFNγ, TNFα and IL-2. Experiments with expanded CMV-specific T cells demonstrated their increased activation following co-cultivation with CMV-pulsed DCs pre-infected with EBOV/VP24m, EBOV/VP35m and EBOV/VP35m/VP24m, as compared to wt EBOV. Both IIDs were found to block phosphorylation of TCR complex-associated adaptors and downstream signaling molecules. Next, we examined the effects of IIDs on the function of B cells in infected PBMC. Infection with EBOV/VP35m and EBOV/VP35m/VP24m resulted in significant increases in the percentages of phenotypically distinct B-cell subsets and plasma cells, as compared to wt EBOV, suggesting inhibition of B cell function and differentiation by VP35 IID. Finally, infection with EBOV/VP35m increased activation of NK cells, as compared to wt EBOV. These results demonstrate a global suppression of cell-mediated responses by EBOV IIDs and identify the role of DCs in suppression of T-cell responses.