CD4 T cell responses to influenza infection

Preschool-age children maintain a distinct memory CD4+ T cell and memory B cell response after SARS-CoV-2 infection

The development of the human immune system lasts for several years after birth. The impact of this maturation phase on the quality of adaptive immunity and the acquisition of immunological memory after infection at a young age remains incompletely defined. Here, using an antigen-reactive T cell (ARTE) assay and multidimensional flow cytometry, we profiled circulating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-reactive CD3+CD4+CD154+ T cells in children and adults before infection, during infection, and 11 months after infection, stratifying children into separate age groups and adults according to disease severity. During SARS-CoV-2 infection, children younger than 5 years old displayed a lower antiviral CD4+ T cell response, whereas children older than 5 years and adults with mild disease had, quantitatively and phenotypically, comparable virus-reactive CD4+ T cell responses. Adults with severe disease mounted a response characterized by higher frequencies of virus-reactive proinflammatory and cytotoxic T cells. After SARS-CoV-2 infection, preschool-age children not only maintained neutralizing SARS-CoV-2-reactive antibodies postinfection comparable to adults but also had phenotypically distinct memory T cells displaying high inflammatory features and properties associated with migration toward inflamed sites. Moreover, preschool-age children had markedly fewer circulating virus-reactive memory B cells compared with the other cohorts. Collectively, our results reveal unique facets of antiviral immunity in humans at a young age and indicate that the maturation of adaptive responses against SARS-CoV-2 toward an adult-like profile occurs in a progressive manner.

COBRA HA and NA vaccination elicits long-live protective immune responses against pre-pandemic H2, H5, and H7 influenza virus subtypes

Highly pathogenic avian influenza (HPAI) viruses remain a major threat to both the poultry industry and human public health, and these viruses continue to spread worldwide. In this study, mice were vaccinated with COBRA H2, H5, and H7 hemagglutinin (HA) and two neuraminidase (NA) proteins, N1 and N2. Vaccinated mice were fully protected against lethal challenge with H5N6 influenza virus. Sera collected after vaccination showed cross-reactive IgG antibodies against a panel of wild-type H2, H5, and H7 HA proteins, and N1 and N2 NA proteins. Mice with pre-existing immunity to H1N1 and H3N2 influenza viruses that were subsequently vaccinated with COBRA HA/NA vaccines had enhanced anti-HA stem antibodies compared to vaccinated mice without pre-existing immunity. In addition, sera collected after vaccination had hemagglutinin inhibitory activity against a panel of H2Nx, H5Nx, and H7Nx influenza viruses. These protective antibodies were maintained up for up to 4 months after vaccination.

Intranasal immunization with an RBD-hemagglutinin fusion protein harnesses preexisting immunity to enhance antigen-specific responses

Intranasal vaccines are anticipated to be powerful tools for combating many infectious diseases, including SARS-CoV-2, because they induce not only systemic immunity but also mucosal immunity at the site of initial infection. However, they are generally inefficient in inducing an antigen-specific immune response without adjuvants. Here, we developed an adjuvant-free intranasal vaccine platform that utilizes the preexisting immunity induced by previous infection or vaccination to enhance vaccine effectiveness. We made RBD-HA, a fusion of the receptor-binding domain (RBD) of spike derived from SARS-CoV-2 as a vaccine target with HA derived from influenza A virus (IAV) as a carrier protein. Intranasal immunization of previously IAV-infected mice with RBD-HA without an adjuvant elicited robust production of RBD-specific systemic IgG and mucosal IgA by utilizing both HA-specific preexisting IgG and CD4+ T cells. Consequently, the mice were efficiently protected from SARS-CoV-2 infection. Additionally, we demonstrated the high versatility of this intranasal vaccine platform by assessing various vaccine antigens and preexisting immunity associated with a variety of infectious diseases. The results of this study suggest the promising potential of this intranasal vaccine platform to address problems associated with intranasal vaccines.

T cell-specific P2RX7 favors lung parenchymal CD4+ T cell accumulation in response to severe lung infections

CD4+ T cells are key components of the immune response during lung infections and can mediate protection against tuberculosis (TB) or influenza. However, CD4+ T cells can also promote lung pathology during these infections, making it unclear how these cells control such discrepant effects. Using mouse models of hypervirulent TB and influenza, we observe that exaggerated accumulation of parenchymal CD4+ T cells promotes lung damage. Low numbers of lung CD4+ T cells, in contrast, are sufficient to protect against hypervirulent TB. In both situations, lung CD4+ T cell accumulation is mediated by CD4+ T cell-specific expression of the extracellular ATP (eATP) receptor P2RX7. P2RX7 upregulation in lung CD4+ T cells promotes expression of the chemokine receptor CXCR3, favoring parenchymal CD4+ T cell accumulation. Our findings suggest that direct sensing of lung eATP by CD4+ T cells is critical to induce tissue CD4+ T cell accumulation and pathology during lung infections.

Structural Framework for Analysis of CD4+ T-Cell Epitope Dominance in Viral Fusion Proteins

Antigen conformation shapes CD4+ T-cell specificity through mechanisms of antigen processing, and the consequences for immunity may rival those from conformational effects on antibody specificity. CD4+ T cells initiate and control immunity to pathogens and cancer and are at least partly responsible for immunopathology associated with infection, autoimmunity, and allergy. The primary trigger for CD4+ T-cell maturation is the presentation of an epitope peptide in the MHC class II antigen-presenting protein (MHCII), most commonly on an activated dendritic cell, and then the T-cell responses are recalled by subsequent presentations of the epitope peptide by the same or other antigen-presenting cells. Peptide presentation depends on the proteolytic fragmentation of the antigen in an endosomal/lysosomal compartment and concomitant loading of the fragments into the MHCII, a multistep mechanism called antigen processing and presentation. Although the role of peptide affinity for MHCII has been well studied, the role of proteolytic fragmentation has received less attention. In this Perspective, we will briefly summarize evidence that antigen resistance to unfolding and proteolytic fragmentation shapes the specificity of the CD4+ T-cell response to selected viral envelope proteins, identify several remarkable examples in which the immunodominant CD4+ epitopes most likely depend on the interaction of processing machinery with antigen conformation, and outline how knowledge of antigen conformation can inform future efforts to design vaccines.

Immune responses in carp strains with different susceptibility to carp edema virus disease

Carp edema virus disease (CEVD), also known as koi sleepy disease (KSD), represents a serious threat to the carp industry. The expression of immune-related genes to CEV infections could lead to the selection of crucial biomarkers of the development of the disease. The expression of a total of eleven immune-related genes encoding cytokines (IL-1β, IL-10, IL-6a, and TNF-α2), antiviral response (Mx2), cellular receptors (CD4, CD8b1, and GzmA), immunoglobulin (IgM), and genes encoding-mucins was monitored in gills of four differently KSD-susceptible strains of carp (Amur wild carp, Amur Sasan, AS; Ropsha scaly carp, Rop; Prerov scaly carp, PS; and koi) on days 6 and 11 post-infection. Carp strains were infected through two cohabitation infection trials with CEV genogroups I or IIa. The results showed that during the infection with both CEV genogroups, KSD-susceptible koi induced an innate immune response with significant up-regulation (p < 0.05) of IL-1β, IL-10, IL-6a, and TNF-α2 genes on both 6 and 11 days post-infection (dpi) compared to the fish sampled on day 0. Compared to koi, AS and Rop strains showed up-regulation of IL-6a and TNF-α2 but no other cytokine genes. During the infection with CEV genogroup IIa, Mx2 was significantly up-regulated in all strains and peaked on 6 dpi in AS, PS, and Rop. In koi, it remained high until 11 dpi. With genogroup I infection, Mx2 was up-expressed in koi on 6 dpi and in PS on both 6 and 11 dpi. No significant differences were noticed in selected mucin genes expression measured in gills of any carp strains exposed to both CEV genogroups. During both CEV genogroups infections, the expression levels of most of the genes for T cell response, including CD4, CD8b1, and GzmA were down-regulated in AS and koi at all time points compared to day 0 control. The expression data for the above experimental trials suggest that both CEV genogroups infections in common carp strains lead to activation of the same expression pattern regardless of the fish's susceptibility towards the virus. The expression of the same genes in AS and koi responding to CEV genogroup IIa infection in mucosal tissues such as gill, gut, and skin showed the significant up-regulation of all the cytokine genes in gill and gut tissues from koi carp at 5 dpi. Significant down-regulation of CD4 and GzmA levels were only detected in koi gill on 5 dpi but not in other tissues. AS carp displayed significant up-expression of Mx2 gene in all mucosal tissues on 5 dpi, whereas in koi, it was up-regulated in gill and gut only. In both carp strains, gill harbored a higher virus load on 5 dpi compared to the other tissues. The results showed that resistance to CEV could not be linked with the selected immune responses measured. The up-regulation of mRNA expression of most of the selected immune-related genes in koi gill and gut suggests that CEV induces a more systemic mucosal immune response not restricted to the target tissue of gills.

CD4+ conventional T cells-related genes signature is a prognostic indicator for ovarian cancer

Introduction

It is believed that ovarian cancer (OC) is the most deadly form of gynecological cancer despite its infrequent occurrence, which makes it one of the most salient public health concerns. Clinical and preclinical studies have revealed that intratumoral CD4+ T cells possess cytotoxic capabilities and were capable of directly killing cancer cells. This study aimed to identify the CD4+ conventional T cells-related genes (CD4TGs) with respect to the prognosis in OC.

Methods

We obtained the transcriptome and clinical data from the Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases. CD4TGs were first identified from single-cell datasets, then univariate Cox regression was used to screen prognosis-related genes, LASSO was conducted to remove genes with coefficient zero, and multivariate Cox regression was used to calculate riskscore and to construct the CD4TGs risk signature. Kaplan-Meier analysis, univariate Cox regression, multivariate Cox regression, time-dependent receiver operating characteristics (ROC), decision curve analysis (DCA), nomogram, and calibration were made to verify and evaluate the risk signature. Gene set enrichment analyses (GSEA) in risk groups were conducted to explore the tightly correlated pathways with the risk group. The role of riskscore has been further explored in the tumor microenvironment (TME), immunotherapy, and chemotherapy. A risk signature with 11 CD4TGs in OC was finally established in the TCGA database and furtherly validated in several GEO cohorts.

Results

High riskscore was significantly associated with a poorer prognosis and proven to be an independent prognostic biomarker by multivariate Cox regression. The 1-, 3-, and 5-year ROC values, DCA curve, nomogram, and calibration results confirmed the excellent prediction power of this model. Compared with the reported risk models, our model showed better performance. The patients were grouped into high-risk and low-risk subgroups according to the riskscore by the median value. The low-risk group patients tended to exhibit a higher immune infiltration, immune-related gene expression and were more sensitive to immunotherapy and chemotherapy.

Discussion

Collectively, our findings of the prognostic value of CD4TGs in prognosis and immune response, provided valuable insights into the molecular mechanisms and clinical management of OC.

Longitudinal Assessment of SARS-CoV-2-Specific T Cell Cytokine-Producing Responses for 1 Year Reveals Persistence of Multicytokine Proliferative Responses, with Greater Immunity Associated with Disease Severity

Cell-mediated immunity is critical for long-term protection against most viral infections, including coronaviruses. We studied 23 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-infected survivors over a 1-year post-symptom onset (PSO) interval by ex vivo cytokine enzyme-linked immunosorbent spot assay (ELISpot) assay. All subjects demonstrated SARS-CoV-2-specific gamma interferon (IFN-γ), interleukin 2 (IL-2), and granzyme B (GzmB) T cell responses at presentation, with greater frequencies in severe disease. Cytokines, mainly produced by CD4⁺ T cells, targeted all structural proteins (nucleocapsid, membrane, and spike) except envelope, with GzmB and IL-2 greater than IFN-γ. Mathematical modeling predicted that (i) cytokine responses peaked at 6 days for IFN-γ, 36 days for IL-2, and 7 days for GzmB, (ii) severe illness was associated with reduced IFN-γ and GzmB but increased IL-2 production rates, and (iii) males displayed greater production of IFN-γ, whereas females produced more GzmB. Ex vivo responses declined over time, with persistence of IL-2 in 86% and of IFN-γ and GzmB in 70% of subjects at a median of 336 days PSO. The average half-life of SARS-CoV-2-specific cytokine-producing cells was modeled to be 139 days (~4.6 months). Potent T cell proliferative responses persisted throughout observation, were CD4 dominant, and were capable of producing all 3 cytokines. Several immunodominant CD4 and CD8 epitopes identified in this study were shared by seasonal coronaviruses or SARS-CoV-1 in the nucleocapsid and membrane regions. Both SARS-CoV-2-specific CD4⁺ and CD8⁺ T cell clones were able to kill target cells, though CD8 tended to be more potent. IMPORTANCE Our findings highlight the relative importance of SARS-CoV-2-specific GzmB-producing T cell responses in SARS-CoV-2 control and shared CD4 and CD8 immunodominant epitopes in seasonal coronaviruses or SARS-CoV-1, and they indicate robust persistence of T cell memory at least 1 year after infection. Our findings should inform future strategies to induce T cell vaccines against SARS-CoV-2 and other coronaviruses.

Immunopeptidomic analysis of influenza A virus infected human tissues identifies internal proteins as a rich source of HLA ligands

CD8+ and CD4+ T cells provide cell-mediated cross-protection against multiple influenza strains by recognising epitopes bound as peptides to human leukocyte antigen (HLA) class I and -II molecules respectively. Two challenges in identifying the immunodominant epitopes needed to generate a universal T cell influenza vaccine are: A lack of cell models susceptible to influenza infection which present population-prevalent HLA allotypes, and an absence of a reliable in-vitro method of identifying class II HLA peptides. Here we present a mass spectrometry-based proteomics strategy for identifying viral peptides derived from the A/H3N2/X31 and A/H3N2/Wisconsin/67/2005 strains of influenza. We compared the HLA-I and -II immunopeptidomes presented by ex-vivo influenza challenged human lung tissues. We then compared these with directly infected immortalised macrophage-like cell line (THP1) and primary dendritic cells fed apoptotic influenza-infected respiratory epithelial cells. In each of the three experimental conditions we identified novel influenza class I and II HLA peptides with motifs specific for the host allotype. Ex-vivo infected lung tissues yielded few class-II HLA peptides despite significant numbers of alveolar macrophages, including directly infected ones, present within the tissues. THP1 cells presented HLA-I viral peptides derived predominantly from internal proteins. Primary dendritic cells presented predominantly viral envelope-derived HLA class II peptides following phagocytosis of apoptotic infected cells. The most frequent viral source protein for HLA-I and -II was matrix 1 protein (M1). This work confirms that internal influenza proteins, particularly M1, are a rich source of CD4+ and CD8+ T cell epitopes. Moreover, we demonstrate the utility of two ex-vivo fully human infection models which enable direct HLA-I and -II immunopeptide identification without significant viral tropism limitations. Application of this epitope discovery strategy in a clinical setting will provide more certainty in rational vaccine design against influenza and other emergent viruses.

Vitamin D in respiratory viral infections: a key immune modulator?

Respiratory viral infections are common respiratory diseases. Influenza viruses, RSV and SARS-COV2 have the potential to cause severe respiratory infections. Numerous studies have shown that unregulated immune response to these viruses can cause excessive inflammation and tissue damage. Therefore, regulating the antiviral immune response in the respiratory tract is of importance. In this regard, recent years studies have emphasized the importance of vitamin D in respiratory viral infections. Although, the most well-known role of vitamin D is to regulate the metabolism of phosphorus and calcium, it has been shown that this vitamin has other important functions. One of these functions is immune regulation. Vitamin D can regulate the antiviral immune response in the respiratory tract in order to provide an effective defense against respiratory viral infections and prevention from excessive inflammatory response and tissue damage. In addition, this vitamin has preventive effects against respiratory viral infections. Some studies during the COVID-19 pandemic have shown that vitamin D deficiency may be associated with a higher risk of mortality and sever disease in patients with COVID-19. Since, more attention has recently been focused on vitamin D. In this article, after a brief overview of the antiviral immune response in the respiratory system, we will review the role of vitamin D in regulating the antiviral immune response comprehensively. Then we will discuss the importance of this vitamin in influenza, RSV, and COVID-19.

Eosinopenia and neutrophil-to-lymphocyte count ratio as prognostic factors in exacerbation of COPD

Exacerbations of Chronic Obstructive Pulmonary Disease (AECOPDs) are one of the most important clinical aspects of the disease, and when requiring hospital admission, they significantly contribute to mortality among COPD patients. Our aim was to assess the role of eosinopenia and neutrophil-to-lymphocyte count (NLR) as markers of in-hospital mortality and length of hospitalization (LoH) among patients with ECOPD requiring hospitalization. We included 275 patients. Eosinopenia was associated with in-hospital deaths only when coexisted with lymphocytopenia, with the specificity of 84.4% (95% CI 79.6-88.6%) and the sensitivity of 100% (95% CI 35.9-100%). Also, survivors presented longer LoH (P < 0.0001). NLR ≥ 13.2 predicted in-hospital death with the sensitivity of 100% (95% CI 35.9-100%) and specificity of 92.6% (95% CI 88.8-95.4%), however, comparison of LoH among survivors did not reach statistical significance (P = 0.05). Additionally, when we assessed the presence of coexistence of eosinopenia and lymphocytopenia first, and then apply NLR, sensitivity and specificity in prediction of in-hospital death was 100% (95% CI 35.9-100) and 93.7% (95% CI 90.1-96.3), respectively. Moreover, among survivors, the occurrence of such pattern was associated with significantly longer LoH: 11 (7-14) vs 7 (5-10) days (P = 0.01). The best profile of sensitivity and specificity in the prediction of in-hospital mortality in ECOPD can be obtained by combined analysis of coexistence of eosinopenia and lymphocytopenia with elevated NLR. The occurrence of a such pattern is also associated with significantly longer LoH among survivors.

DNA Methylation Patterns in CD4+ T Cells of Naïve and Influenza A Virus-Infected Mice Developmentally Exposed to an Aryl Hydrocarbon Receptor Ligand

BACKGROUND

Early life environmental exposures can have lasting effects on the function of the immune system and contribute to disease later in life. Epidemiological studies have linked early life exposure to xenobiotics that bind the aryl hydrocarbon receptor (AhR) with dysregulated immune responses later in life. Among the immune cells influenced by developmental activation of the AhR are CD 4 + T cells. Yet, the underlying affected cellular pathways via which activating the AhR early in life causes the responses of CD 4 + T cells to remain affected into adulthood remain unclear.

OBJECTIVE

Our goal was to identify cellular mechanisms that drive impaired CD 4 + T-cell responses later in life following maternal exposure to an exogenous AhR ligand.

METHODS

C57BL/6 mice were vertically exposed to the prototype AhR ligand, 2,3,7,8-tetrachlorodibenzo-p -dioxin (TCDD), throughout gestation and early postnatal life. The transcriptome and DNA methylation patterns were evaluated in CD 4 + T cells isolated from naïve and influenza A virus (IAV)-infected adult mice that were developmentally exposed to TCDD or vehicle control. We then assessed the influence of DNA methylation-altering drug therapies on the response of CD 4 + T cells from developmentally exposed mice to infection.

RESULTS

Gene and protein expression showed that developmental AhR activation reduced CD 4 + T-cell expansion and effector functions during IAV infection later in life. Furthermore, whole-genome bisulfite sequencing analyses revealed that developmental AhR activation durably programed DNA methylation patterns across the CD 4 + T-cell genome. Treatment of developmentally exposed offspring with DNA methylation-altering drugs alleviated some, but not all, of the impaired CD 4 + T-cell responses.

DISCUSSION

Taken together, these results indicate that skewed DNA methylation is one of the mechanisms by which early life exposures can durably change the function of T cells in mice. Furthermore, treatment with DNA methylation-altering drugs after the exposure restored some aspects of CD 4 + T-cell functional responsiveness. https://doi.org/10.1289/EHP7699.

High- and low-molecular-weight chitosan act as adjuvants during single-dose influenza A virus protein vaccination through distinct mechanisms

The investigation of new adjuvants is essential for the development of efficacious vaccines. Chitosan (CS), a derivative of chitin, has been shown to act as an adjuvant, improving vaccine-induced immune responses. However, the effect of CS molecular weight (MW) on this adjuvanticity has not been investigated, despite MW having been shown to impact CS biological properties. Here, two MW variants of CS were investigated for their ability to enhance vaccine-elicited immune responses in vitro and in vivo, using a single-dose influenza A virus (IAV) protein vaccine model. Both low-molecular-weight (LMW) and high-molecular-weight (HMW) CS-induced interferon regulatory factor pathway signaling, antigen-presenting cell activation, and cytokine messenger RNA (mRNA) production, with LMW inducing higher mRNA levels at 24 h and HMW elevating mRNA responses at 48 h. LMW and HMW CS also induced adaptive immune responses after vaccination, indicated by enhanced immunoglobulin G production in mice receiving LMW CS and increased CD4 interleukin 4 (IL-4) and IL-2 production in mice receiving HMW CS. Importantly, both LMW and HMW CS adjuvantation reduced morbidity following homologous IAV challenge. Taken together, these results support that LMW and HMW CS can act as adjuvants, although this protection may be mediated through distinct mechanisms based on CS MW.

Dynamic Natural Killer Cell and T Cell Responses to Influenza Infection

Influenza viruses have perplexed scientists for over a hundred years. Yearly vaccines limit their spread, but they do not prevent all infections. Therapeutic treatments for those experiencing severe infection are limited; further advances are held back by insufficient understanding of the fundamental immune mechanisms responsible for immunopathology. NK cells and T cells are essential in host responses to influenza infection. They produce immunomodulatory cytokines and mediate the cytotoxic response to infection. An imbalance in NK and T cell responses can lead to two outcomes: excessive inflammation and tissue damage or insufficient anti-viral functions and uncontrolled infection. The main cause of death in influenza patients is the former, mediated by hyperinflammatory responses termed “cytokine storm.” NK cells and T cells contribute to cytokine storm, but they are also required for viral clearance. Many studies have attempted to distinguish protective and pathogenic components of the NK cell and T cell influenza response, but it has become clear that they are dynamic and integrated processes. This review will analyze how NK cell and T cell effector functions during influenza infection affect the host response and correlate with morbidity and mortality outcomes.

Immune-engineered H7N9 influenza hemagglutinin improves protection against viral influenza virus challenge

The influenza hemagglutinin (HA) isolated from avian H7N9 influenza virus strains elicit weak immune responses. This low immunogenicity may be due to a regulatory T cell (T_reg)-stimulating epitopes in HA from the H7N9 isolate A/Anhui/1/2013 (Anh/13). In this report, this T_reg stimulating sequence was removed from the wild-type (WT) H7 HA amino acid sequence and replaced with a conserved CD4 + T cell stimulating sequences from human seasonal H3N2 strains and designed OPT1 H7 HA. The effectiveness of this optimized H7 HA protein was determined using a humanized mouse (HLA-DR3) expressing the human leukocyte antigen (HLA) DR3 allele. HLA-DR3 mice were pre-immunized by infecting with H3N2 influenza virus, A/Hong Kong/4108/2014 and then vaccinated intramuscularly with either the WT H7 HA from Anh/13 or the OPT1 H7 HA antigen without adjuvant. The OPT1 H7 HA vaccination group elicited higher H7 HA-specific IgG titers that resulted in a lower mortality, weight loss, and lung viral titer following lethal challenge with the H7N9 Anh/13 influenza virus compared to WT-vaccinated mice. Overall, T-cell epitope-engineered vaccines can improve the immunogenicity of H7 HA antigens resulting in enhanced survival and lower morbidity against H7N9 influenza virus challenge.

The cellular immunophenotype expression of influenza A virus and influenza B virus infection in children

BACKGROUND

The innate immune response is the primary defense against influenza virus infection.

METHODS

This is a prospective study carried out in children <18 years of age who were diagnosed with influenza A or influenza B infection. Demographic and clinical data, laboratory findings and cell immunophenotypes on first presentation were compared.

RESULTS

With respect to immunophenotype, influenza A infection resulted in a higher fraction of CD14⁺ and CD4⁺IL-17A⁺cells compared to children infected with influenza B. By contrast, influenza B infection resulted in a comparatively higher percentage of double-negative CD4^-CD8^- lymphocyte subsets. Influenza A infection was associated with comparatively higher percentages of CD4⁺CD25^highFoxp3⁺ and CD4⁺CD25^lowFoxp3⁺ cells. By contrast, the percentage of CD8⁺CD25^high and CD8⁺CD25^low cells was similar among patients with influenza A infection and influenza B infection.

CONCLUSIONS

An improved understanding of the fraction of regulatory T cells with influenza virus infections may provide further understandings on immune responses.

Influenza sequelae: from immune modulation to persistent alveolitis

Acute influenza virus infections are a global public health concern accounting for millions of illnesses worldwide ranging from mild to severe with, at time, severe complications. Once an individual is infected, the immune system is triggered in response to the pathogen. This immune response can be beneficial ultimately leading to the clearance of the viral infection and establishment of immune memory mechanisms. However, it can be detrimental by increasing susceptibility to secondary bacterial infections and resulting in permanent changes to the lung architecture, in the form of fibrotic sequelae. Here, we review influenza associated bacterial super-infection, the formation of T-cell memory, and persistent lung injury resulting from influenza infection.

Double-Layered M2e-NA Protein Nanoparticle Immunization Induces Broad Cross-Protection against Different Influenza Viruses in Mice

The development of a universal influenza vaccine is an ideal strategy to eliminate public health threats from influenza epidemics and pandemics. This ultimate goal is restricted by the low immunogenicity of conserved influenza epitopes. Layered protein nanoparticles composed of well-designed conserved influenza structures have shown improved immunogenicity with new physical and biochemical features. Herein, structure-stabilized influenza matrix protein 2 ectodomain (M2e) and M2e-neuraminidase fusion (M2e-NA) recombinant proteins are generated and M2e protein nanoparticles and double-layered M2e-NA protein nanoparticles are produced by ethanol desolvation and chemical crosslinking. Immunizations with these protein nanoparticles induce immune protection against different viruses of homologous and heterosubtypic NA in mice. Double-layered M2e-NA protein nanoparticles induce higher levels of humoral and cellular responses compared with their comprising protein mixture or M2e nanoparticles. Strong cytotoxic T cell responses are induced in the layered M2e-NA protein nanoparticle groups. Antibody responses contribute to the heterosubtypic NA immune protection. The protective immunity is long lasting. These results demonstrate that double-layered protein nanoparticles containing structure-stabilized M2e and NA can be developed into a universal influenza vaccine or a synergistic component of such vaccines. Layered protein nanoparticles can be a general vaccine platform for different pathogens.

Kinetics and Phenotype of the CD4 T Cell Response to Influenza Virus Infections

Influenza A virus (IAV) is a leading cause of respiratory infections, with increased risk of severe illness and death in the very young, aged, and immunocompromised individuals. In both mice and humans, IAV-specific T cell responses are protective during primary as well as homologous and heterologous challenge infections. Many mouse studies have focused on CD4 T cells specific for a single, known model or IAV antigen. However, studies have demonstrated that the IAV-specific CD4 T cell response comprises many epitopes spread across multiple viral proteins. Therefore, herein we track the antigen-experienced CD4 T cell response using the surrogate markers CD49d and CD11a. This novel surrogate marker method allows us to characterize the full IAV-specific CD4 T cell response without the potential bias that could occur when examining an individual Ag-specificity. Our findings demonstrate that the immunodominant I-A^b-binding NP_311−325 epitope often used in studies of IAV-specific CD4 T cells represents only about 5% of the total IAV-specific CD4 T cell response. Further, we find that the kinetics of the full pulmonary CD4 T cell response is similar to that of NP₃₁₁-specific T cells and that the full CD4 T cell response in the lungs is predominantly composed of cells expressing the Th1 transcription factor T-bet, with smaller but significant portions of the response expressing the Treg and Tfh associated transcription factors Foxp3 and Bcl-6, respectively. Interestingly, although Th1 cells are the most abundant Th subset in the lungs of both BALB/c and C57Bl/6 mice following IAV, the relative abundance of Treg and Tfh is reversed in the different mouse strains. In BALB/c mice, Foxp3⁺ cells are more abundant than Bcl6⁺ cells, whereas in C57Bl/6 mice, there are more Bcl6⁺ cells. As a whole, these data highlight the diversity of the endogenous CD4 T cell response to a primary IAV infection, providing an important context for past and future studies of the IAV-specific CD4 T cell response.

Dendritic cell NLRC4 regulates influenza A virus-specific CD4 T cell responses through FasL expression

Influenza A virus (IAV)-specific T cell responses are important correlates of protection during primary and subsequent infections. Generation and maintenance of robust IAV-specific T cell responses relies on T cell interactions with dendritic cells (DCs). In this study, we explore the role of nucleotide-binding domain leucine-rich repeat containing receptor family member NLRC4 in modulating the DC phenotype during IAV infection. Nlrc4-/- mice had worsened survival and increased viral titers during infection, normal innate immune cell recruitment and IAV-specific CD8 T cell responses, but severely blunted IAV-specific CD4 T cell responses compared to wild-type mice. The defect in the pulmonary IAV-specific CD4 T cell response was not a result of defective priming or migration of these cells in Nlrc4-/- mice but was instead due to an increase in FasL+ DCs, resulting in IAV-specific CD4 T cell death. Together, our data support a novel role for NLRC4 in regulating the phenotype of lung DCs during a respiratory viral infection, and thereby influencing the magnitude of protective T cell responses.

Virtual memory cells make a major contribution to the response of aged influenza-naïve mice to influenza virus infection

Background

A diverse repertoire of naïve T cells is thought to be essential for a robust response to new infections. However, a key aspect of aging of the T cell compartment is a decline in numbers and diversity of peripheral naïve T cells. We have hypothesized that the age-related decline in naïve T cells forces the immune system to respond to new infections using cross-reactive memory T cells generated to previous infections that dominate the aged peripheral T cell repertoire.

Results

Here we confirm that the CD8 T cell response of aged, influenza-naïve mice to primary infection with influenza virus is dominated by T cells that derive from the memory T cell pool. These cells exhibit the phenotypic characteristics of virtual memory cells rather than true memory cells. Furthermore, we find that the repertoire of responding CD8 T cells is constrained compared with that of young mice, and differs significantly between individual aged mice. After infection, these virtual memory CD8 T cells effectively develop into granzyme-producing effector cells, and clear virus with kinetics comparable to naïve CD8 T cells from young mice.

Conclusions

The response of aged, influenza-naive mice to a new influenza infection is mediated largely by memory CD8 T cells. However, unexpectedly, they have the phenotype of VM cells. In response to de novo influenza virus infection, the VM cells develop into granzyme-producing effector cells and clear virus with comparable kinetics to young CD8 T cells.

Enhanced infection of avian influenza virus H9N2 with infectious laryngeotracheitis vaccination in chickens

Avian influenza and infectious laryngeotracheitis viruses are common causes of respiratory diseases in chickens with economical importance worldwide. In this study, we investigated the effect of experimental co-infection of avian influenza virus-H9N2 (AIV-H9N2) with infectious laryngeotracheitis virus (ILTV) live-attenuated vaccine (LAR-VAC^®) on chickens. Four experimental groups were included in this study: negative control group, AIV-H9N2 group, AIV-H9N2+LAR-VAC^® group, and LAR-VAC^® group. AIV-H9N2 was inoculated intranasally to challenged groups at 35 days of age. On the same day, LAR-VAC^® was ocularly administered to vaccinated groups. Chickens were observed for clinical signs, changes in body weight and mortality rates. Tissue samples, sera, tracheal and cloacal swabs, and blood were also collected at 3, 6, 9 and 12 days post-infection (PI). A significant increase in clinical signs and mortality rates were observed in the AIV-H9N2 + LAR-VAC^® group. Moreover, chickens coinfected with AIV-H9N2 and LAR-VAC^® showed a significant decrease in body weight and lymphoid organs indices. The tracheal gross and histopathological lesions and the shedding titer and period of AIV-H9N2 were significantly higher in AIV-H9N2 + LAR-VAC^® group when compared to other groups. Furthermore, AIV-H9N2 infection leads to humoral and cellular immunosuppression as shown by a significant decrease in the CD4⁺/CD8⁺ ratio and antibody responses to ILTV and a significant increase in H/L ratio. In conclusion, this is the first report of co-infection of AIV-H9N2 and ILTV vaccine in chickens, which leads to increased pathogenicity, pathological lesions, and AIV-H9N2 shedding titer and period, which can lead to severe economic losses due to poor weight gain and mortality.

Diverse Epitope Specificity, Immunodominance Hierarchy, and Functional Avidity of Effector CD4 T Cells Established During Priming Is Maintained in Lung After Influenza A Virus Infection

One of the major contributions to protective immunity to influenza viruses that is provided by virus-specific CD4 T cells is delivery of effector function to the infected lung. However, there is little known about the selection and breadth of viral epitope-specific CD4 T cells that home to the lung after their initial priming. In this study, using a mouse model of influenza A infection and an unbiased method of epitope identification, the viral epitope-specific CD4 T cells elicited after infection were identified and quantified. We found that a very diverse specificity of CD4 T cells is primed by infection, including epitopes from hemagglutinin, neuraminidase, matrix protein, nucleoprotein, and non-structural protein-1. Using peptide-specific cytokine EliSpots, the diversity and immunodominance hierarchies established in the lung-draining lymph node were compared with specificities of CD4 T cells that home to the lung. Our studies revealed that CD4 T cells of all epitope specificities identified in peripheral lymphoid tissue home back to the lung and that most of these lung-homing cells are localized within the tissue rather than the pulmonary vasculature. There is a striking shift of CD4 T cell functionality that enriches for IFN-γ production as cells are primed in the lymph node, enter the lung vasculature, and finally establish residency in the tissue, but with no apparent shifts in their functional avidity. We conclude that CD4 T cells of broad viral epitope specificity are recruited into the lung after influenza infection, where they then have the opportunity to encounter infected or antigen-bearing antigen-presenting cells.

The impact of aging on CD4+ T cell responses to influenza infection

CD4⁺ T cells are important for generating high quality and robust immune responses to influenza infection. Immunosenescence that occurs with aging, however, compromises the ability of CD4⁺ T cells to differentiate into functional subsets resulting in a multitude of dysregulated responses namely, delayed viral clearance and prolonged inflammation leading to increased pathology. Current research employing animal models and human subjects has provided new insights into the description and mechanisms of age-related CD4⁺ T cell changes. In this review, we will discuss the consequences of aging on CD4⁺ T cell differentiation and function and how this influences the initial CD4⁺ T cell effector responses to influenza infection. Understanding these age-related alterations will aid in the pharmacological development of therapeutic treatments and improved vaccination strategies for the vulnerable elderly population.

The safety of influenza vaccine in clinically cured leprosy patients in China

Background: Leprosy is an infectious disease caused by the bacterium Mycobacterium leprae. Influenza vaccine is an important influenza prevention strategy and the preparations used display good safety and tolerability profiles. But the safety of applying influenza vaccine on the clinical cured leprosy patients is unclear.

Methods: We conducted an observational clinical study, in Wuhan between November 15, 2016 and March 1, 2017. Two groups of participants ≥50 years of age received a 0.5 ml dose of the inactivated split-virion trivalent influenza vaccine and a follow-up 28 days observation of any solicited and unsolicited adverse events.

Results: A total of 134 subjects were included in the study. The total rate of reactogenicity was 5.4% [2/37] in leprosy group and 15.5% [15/ 97] in control group, the difference of reactogenicity between two groups was not significant (p = 0.1522). For solicited injection-sites adverse events (AEs), 12.4% [12/ 97] participants in the control group reported of itching, pain, erythema, swelling or induration, and no participants in leprosy group reported of any solicited injection-sites AEs. For solicited systemic AEs, 7.2% [7 / 97] participants in the control group reported of fever, malaise or headache, and 2.7% [1 / 37] participants in the leprosy group reported of fever, statistic result showed that the difference was not significant (p = 0.4438). Unsolicited AEs was reported by one male aged 76, 4 hours after vaccination administration, his plantar ulcer area began bleeding. All AEs were grade 1 or grade 2, and no recurrence of lepra reaction, AEs leading to early withdrawal from the study, or deaths were reported in this study.

Conclusions: To our knowledge, the present study is the first clinical study to evaluate the safety of influenza vaccine in clinically cured leprosy patients. We concluded that clinically cured leprosy patients are relatively safe for influenza vaccine. More importantly, our study make a positive and scientific efforts to eradicate discrimination on leprosy. In our study, we described a patient with plantar ulcer undergoing bleeding for 4 hours after vaccine administration. Based on evidence we have, we interpret that this adverse event may probably associated with vaccine, and patients with ulcer and leprosy need intensive attention after vaccines administration.

Cross-Protective Efficacy of Influenza Virus M2e Containing Virus-Like Particles Is Superior to Hemagglutinin Vaccines and Variable Depending on the Genetic Backgrounds of Mice

Influenza virus M2 extracellular domain (M2e) has been a target for developing cross-protective vaccines. However, the efficacy and immune correlates of M2e vaccination are poorly understood in the different host genetic backgrounds in comparison with influenza vaccines. We previously reported the cross-protective efficacy of virus-like particle (M2e5x VLP) vaccines containing heterologous tandem M2e repeats (M2e5x) derived from human, swine, and avian influenza viruses. In this study to gain better understanding of cross-protective influenza vaccines, we compared immunogenicity and efficacy of M2e5x VLP, H5 hemagglutinin VLP (HA VLP), and inactivated H3N2 virus (H3N2i) in wild-type strains of BALB/c and C57BL/6 mice, and CD4 and CD8 knockout (KO) mice. M2e5x VLP was superior to HA VLP in conferring cross-protection whereas H3N2i inactivated virus vaccine provided high efficacy of homologous protection. After M2e5x VLP vaccination and challenge, BALB/c mice induced higher IgG responses, lower lung viral loads, and less body weight loss when compared with those in C57BL/6 mice. M2e5x VLP but not H3N2i immune mice after primary challenges developed strong immunity against a secondary heterosubtypic virus as a model of future pandemics. M2e5x VLP and HA VLP vaccines were able to raise IgG isotypes in CD4 KO mice. T cells were found to contribute to cross-protection by playing a role in reducing lung viral loads. In conclusion, M2e5x VLP vaccination induced better cross-protection than HA VLP, and its efficacy varied depending on the genetic backgrounds of mice, supporting the important roles of T cells.

Mechanistic perspective of the oxido-immunopathologic resolution property of kolaviron in mice influenza pneumonitis

Implicated in influenza-associated pathology are innate defence overzealousness and unabated secretion of oxidative tissue-sensitive antimicrobial agents. At different time points, mice were pre-treated with kolaviron (400 mg/kg), a natural antioxidant and anti-inflammatory agent, and subsequently challenged with 2 LD₅₀ influenza A/H3N2/Perth/16/09 virus. After euthanasia at day 6, blood, lungs, liver and spleen were collected and processed for biochemical, immunohistochemical and flow cytometric assessment of redo-inflammatory imbalance, cytokine storm indices and T helper 1 host response. Previously kolaviron was reported to delay mortality onset, improve morbidity and attenuate myeloperoxidase activity and nitric oxide production with minimal impact on viral clearance. This study additionally confirmed nitric oxide, but not hydrogen peroxide, as the major culprit implicated in influenza virus-induced oxido-pathology. Systemic effect of the sustained inflammation and nitrosative stress was more prominent in the spleen and lung than in the liver of mice infected with A/H3N2/Perth/16/09. Influential to immunopathology was heightened pulmonary expression of IL-1β, RANTES, IL-10, MCP-1, NF-κB, iNOS and COX-2. However, kolaviron combated the influenza-established nitrative stress, reversed the elicited cytokine storm and restored the oxidized environment to a reductive milieu. Our data also suggest that kolaviron administration early in infection may foster CD4⁺ response. These data indicate that kolaviron may confer disease-dwindling properties during acute influenza infection via a system-wide protective approach involving multiple targets especially at the early stage of the infection.

Immune Responses to Influenza Virus and Its Correlation to Age and Inherited Factors

Influenza viruses belong to the family Orthomyxoviridae of enveloped viruses and are an important cause of respiratory infections worldwide. The influenza virus is able to infect a wide variety species as diverse as poultry, marine, pigs, horses, and humans. Upon infection with influenza virus the innate immunity plays a critical role in efficient and rapid control of viral infections as well as in adaptive immunity initiation. The humoral immune system produces antibodies against different influenza antigens, of which the HA-specific antibody is the most important for neutralization of the virus and thus prevention of illness. Cell mediated immunity including CD4+ helper T cells and CD8+ cytotoxic T cells are the other arms of adaptive immunity induced upon influenza virus infection. The complex inherited factors and age related changes are associated with the host immune responses. Here, we review the different components of immune responses against influenza virus. Additionally, the correlation of the immune response to age and inherited factors has been discussed. These determinations lead to a better understanding of the limitations of immune responses for developing improved vaccines to control influenza virus infection.

Influenza virus infection exacerbates experimental autoimmune encephalomyelitis disease by promoting type I T cells infiltration into central nervous system

Multiple sclerosis starts with increased migration of auto-reactive lymphocytes across the blood-brain barrier, resulting in persistent neurodegeneration. Clinical and epidemiological studies indicated upper respiratory viral infections are associated with clinical exacerbation of multiple sclerosis. However, so far there is no any direct evidence to support it. Using the experimental autoimmune encephalomyelitis mice as the model for multiple sclerosis, we demonstrated that mice experienced with influenza virus infection were unable to recover from experimental autoimmune encephalomyelitis with a long-term exacerbation. The exacerbated disease was due to more type I T cells, such as CD45^highCD4⁺CD44^high, CD45^highCD4⁺CCR5⁺, CD45^high IFNγ⁺CD4⁺, MOG_35-55-specific IFNγ⁺CD4⁺ and influenza virus-specific IFNγ⁺CD4⁺ T cells, infiltrating central nervous system in mice with prior influenza virus infection. Influenza virus infection created a notable inflammatory environment in lung and mediastinal lymph node after influenza virus inoculation, suggesting the lung may constitute an inflammatory niche in which auto-aggressive T cells gain the capacity to enter CNS. Indeed, the early stage of EAE disease was accompanied by increased CCR5⁺CD4⁺, CXCR3⁺CD4⁺ T cell and MOG_35-55 specific CD4⁺ T cells localized in the lung in influenza virus-infected mice. CCL5/CCR5 might mediate the infiltration of type I T cells into CNS during the disease development after influenza infection. Administration of CCR5 antagonist could significantly attenuate the exacerbated disease. Our study provided the evidence that the prior influenza virus infection may promote the type I T cells infiltration into the CNS, and subsequently cause a long-term exacerbation of experimental autoimmune encephalomyelitis.

Delta inulin-derived adjuvants that elicit Th1 phenotype following vaccination reduces respiratory syncytial virus lung titers without a reduction in lung immunopathology

Respiratory syncytial virus (RSV) is a significant cause of lower respiratory tract infections resulting in bronchiolitis and even mortality in the elderly and young children/infants. Despite the impact of this virus on human health, no licensed vaccine exists. Unlike many other viral infections, RSV infection or vaccination does not induce durable protective antibodies in humans. In order to elicit high titer, neutralizing antibodies against RSV, we investigated the use of the adjuvant Advax™, a novel polysaccharide adjuvant based on delta inulin microparticles, to enhance antibody titers following vaccination. BALB/c mice were vaccinated intramuscularly with live RSV as a vaccine antigen in combination with one of two formulations of Advax™. Advax-1 was comprised of the standard delta inulin adjuvant and Advax-2 was formulated delta inulin plus CpG oligodendronucleotides (ODNs). An additional group of mice were either mock vaccinated, immunized with vaccine only, or administered vaccine plus Imject Alum. Following 3 vaccinations, mice had neutralizing antibody titers that correlated with reduction in viral titers in the lungs. Advax-1 significantly enhanced serum RSV-specific IgG1 levels at week 6 indicative of a Th2 response, similar to titers in mice administered vaccine plus Imject Alum. In contrast, mice vaccinated with vaccine plus Advax-2 had predominately IgG2a titers indicative of a Th1 response that was maintained during the entire study. Interestingly, regardless of which AdvaxTM adjuvant was used, the neutralizing titers were similar between groups, but the viral lung titers were significantly lower (∼10E+3pfu/g) in mice administered vaccine with either AdvaxTM adjuvant compared to mice administered adjuvants only. The lung pathology in vaccinated mice with AdvaxTM was similar to Imject Alum. Overall, RSV vaccine formulated with AdvaxTM had high neutralizing antibody titers with low lung viral titers, but exacerbated lung pathology compared to unvaccinated mice.

Topical CpG Oligodeoxynucleotide Adjuvant Enhances the Adaptive Immune Response against Influenza A Infections

Current influenza vaccines generate humoral immunity, targeting highly variable epitopes and thus fail to achieve long-term protection. T cells recognize and respond to several highly conserved epitopes across influenza serotypes. A strategy of raising strong cytotoxic T cell memory responses to epitopes conserved across serotypes would provide cross serotype protection, eliminating the need for annual vaccination. We explored the adjuvant potential of epicutaneous (ec) and subcutaneous (sc) delivery of CpG oligodeoxynucleotide in conjunction with sc protein immunization to improve protection against influenza A virus (IAV) infections using a mouse model. We found enhanced long-term protection with epicutaneous CpG ODN (ecCpG) compared to subcutaneous CpG ODN (scCpG) as demonstrated by reduced viral titers in the lungs. This correlated with increased antigen-specific CD8 T cells in the airways and the lungs. The memory T cell response after immunization with ecCpG adjuvant was comparable to memory response by priming with IAV infection in the lungs. In addition, ecCpG was more efficient than scCpG in inducing the generation of IFN-γ producing CD4 T cells. The adjuvant effect of ecCpG was accompanied with its ability to modulate tissue-homing molecules on T cells that may direct them to the site of infection. Together, this work provides evidence for using ecCpG to induce strong antibody and memory T cell responses to confer protection against IAV infection.

NADPH Oxidase 1 Is Associated with Altered Host Survival and T Cell Phenotypes after Influenza A Virus Infection in Mice

The role of the reactive oxygen species-producing NADPH oxidase family of enzymes in the pathology of influenza A virus infection remains enigmatic. Previous reports implicated NADPH oxidase 2 in influenza A virus-induced inflammation. In contrast, NADPH oxidase 1 (Nox1) was reported to decrease inflammation in mice within 7 days post-influenza A virus infection. However, the effect of NADPH oxidase 1 on lethality and adaptive immunity after influenza A virus challenge has not been explored. Here we report improved survival and decreased morbidity in mice with catalytically inactive NADPH oxidase 1 (Nox1*/Y) compared with controls after challenge with A/PR/8/34 influenza A virus. While changes in lung inflammation were not obvious between Nox1*/Y and control mice, we observed alterations in the T cell response to influenza A virus by day 15 post-infection, including increased interleukin-7 receptor-expressing virus-specific CD8+ T cells in lungs and draining lymph nodes of Nox1*/Y, and increased cytokine-producing T cells in lungs and spleen. Furthermore, a greater percentage of conventional and interstitial dendritic cells from Nox1*/Y draining lymph nodes expressed the co-stimulatory ligand CD40 within 6 days post-infection. Results indicate that NADPH oxidase 1 modulates the innate and adaptive cellular immune response to influenza virus infection, while also playing a role in host survival. Results suggest that NADPH oxidase 1 inhibitors may be beneficial as adjunct therapeutics during acute influenza infection.

Targeting of nucleoprotein to chemokine receptors by DNA vaccination results in increased CD8(+)-mediated cross protection against influenza

Vaccination is at present the most efficient way of preventing influenza infections. Currently used inactivated influenza vaccines can induce virus-neutralizing antibodies that are protective against a particular influenza strain, but hamper the induction of cross-protective T-cell responses to later infections. Thus, influenza vaccines need to be updated annually in order to confer protection against circulating influenza strains. This study aims at developing an efficient vaccine that can induce broader protection against influenza. For this purpose, we have used the highly conserved nucleoprotein (NP) from an influenza A virus subtype H7N7 strain, and inserted it into a vaccine format that targets an antigen directly to relevant antigen presenting cells (APCs). The vaccine format consists of bivalent antigenic and targeting units, linked via an Ig-based dimerization unit. In this study, NP was linked to MIP-1α, a chemokine that targets the linked antigen to chemokine receptors 1, 3 and 5 expressed on various APCs. The vaccine protein was indirectly delivered by DNA. Mice were vaccinated intradermally with plasmids, in combination with electroporation to enhance cellular uptake of DNA. We found that a single DNA vaccination was sufficient for induction of both antibody and T cell responses in BALB/c mice. Targeting of nucleoprotein to chemokine receptors enhanced T cell responses but not antibody responses. Moreover, a single dose of MIP1α-NP conferred protection in BALB/c mice against a lethal challenge with an H1N1 influenza virus. The observed cross-protection was mediated by CD8(+) T cells.

Emerging Infections of CNS: Avian Influenza A Virus, Rift Valley Fever Virus and Human Parechovirus

History is replete with emergent pandemic infections that have decimated the human population. Given the shear mass of humans that now crowd the earth, there is every reason to suspect history will repeat itself. We describe three RNA viruses that have recently emerged in the human population to mediate severe neurological disease. These new diseases are results of new mutations in the infectious agents or new exposure pathways to the agents or both. To appreciate their pathogenesis, we summarize the essential virology and immune response to each agent. Infection is described in the context of known host defenses. Once the viruses evade immune defenses and enter central nervous system (CNS) cells, they rapidly co-opt host RNA processing to a cataclysmic extent. It is not clear why the brain is particularly susceptible to RNA viruses; but perhaps because of its tremendous dependence on RNA processing for physiological functioning, classical mechanisms of host defense (eg, interferon disruption of viral replication) are diminished or not available. Effectiveness of immunity, immunization and pharmacological therapies is reviewed to contextualize the scope of the public health challenge. Unfortunately, vaccines that confer protection from systemic disease do not necessarily confer protection for the brain after exposure through unconventional routes.

Activation of the aryl hydrocarbon receptor during development enhances the pulmonary CD4+ T-cell response to viral infection

Respiratory infections are a threat to health and economies worldwide, yet the basis for striking variation in the severity of infection is not completely understood. Environmental exposures during development are associated with increased severity and incidence of respiratory infection later in life. Many of these exposures include ligands of the aryl hydrocarbon receptor (AHR), a transcription factor expressed by immune and nonimmune cells. In adult animals, AHR activation alters CD4(+) T cells and changes immunopathology. Developmental AHR activation impacts CD4(+) T-cell responses in lymphoid tissues, but whether skewed responses are also present in the infected lung is unknown. To determine whether pulmonary CD4(+) T-cell responses are modified by developmental AHR activation, mice were exposed to the prototypical AHR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin during development and infected with influenza virus as adults. Lungs of exposed offspring had greater bronchopulmonary inflammation compared with controls, and activated, virus-specific CD4(+) T cells contributed to the infiltrating leukocytes. These effects were CD4(+) T cell subset specific, with increases in T helper type 1 and regulatory T cells, but no change in the frequency of T helper type 17 cells in the infected lung. This is in direct contrast to prior reports of suppressed conventional CD4(+) T-cell responses in the lymph node. Using adoptive transfers and manipulating the pathogen properties, we determined that developmental exposure influenced factors intrinsic and extrinsic to CD4(+) T cells and may involve developmentally induced changes in signals from infected lung epithelial cells. Thus developmental exposures lead to context-dependent changes in pulmonary CD4(+) T-cell subsets, which may contribute to differential responses to respiratory infection.

Longevity of B-cell and T-cell responses after live attenuated influenza vaccination in children

Background. The live attenuated influenza vaccine (LAIV) is the preferred vaccine for children, but the mechanisms behind protective immune responses are unclear, and the duration of immunity remains to be elucidated. This study reports on the longevity of B-cell and T-cell responses elicited by the LAIV.

Methods. Thirty-eight children (3–17 years old) were administered seasonal LAIV. Blood samples were collected before vaccination with sequential sampling up to 1 year after vaccination. Humoral responses were evaluated by a hemagglutination inhibition assay, and memory B-cell responses were evaluated by an enzyme-linked immunosorbent spot assay (ELISpot). T-cell responses were evaluated by interferon γ (IFN-γ) ELISpot analysis, and intracellular cytokine staining of CD4⁺ T cells for detection of IFN-γ, interleukin 2, and tumor necrosis factor α was performed using flow cytometry.

Results. LAIV induced significant increases in B-cell and T-cell responses, which were sustained at least 1 year after vaccination. Strain variations were observed, in which the B strain elicited stronger responses. IFN-γ–expressing T cell counts increased significantly, and remained higher than prevaccination levels 1 year later. Expression of T-helper type 1 intracellular cytokines (interleukin 2, IFN-γ, and tumor necrosis factor α) increased after 1 dose and were boosted after the second dose. Hemagglutination inhibition titers were sustained for 1 year. Vaccine-induced memory B cell counts were significantly increased, and the response persisted for one year.

Conclusions. LAIV elicited B-cell and T-cell responses that persisted for at least 1 year in children. This is a novel finding that will aid future vaccine policy.

Local and systemic immune response in pigs during subclinical and clinical swine influenza infection

Local and systemic immune responses in pigs intranasally (IN) and intratracheally (IT) inoculated with swine influenza virus (SIV) were studied. No clinical signs were observed in IN-inoculated pigs, while IT-inoculated pigs developed typical signs of influenza. Significantly higher titres of specific antibodies and changes of haematological parameters were found only in IT-inoculated pigs. Because positive correlations between viral titre, local cytokine concentration, and lung pathology have been observed, we hypothesise that both viral load and the local secretion of cytokines play a role in the induction of lung lesions. It could be that a higher replication of SIV stimulates immune cells to secrete higher amounts of cytokines. The results of the present study indicate that pathogenesis of SIV is dependent on both, the damage caused to the lung parenchyma directly by virus, and the effects on the cells of the host's immune system.

Conserved peptides containing overlapping CD4+ and CD8+ T-cell epitopes in the H1N1 influenza virus: an immunoinformatics approach

Pandemic threats of the H1N1 influenza virus have drawn attention to developing a universal vaccine against circulating and future strains of this virus. An immunoinformatics study was conducted to identify conserved peptides containing CD4+ and CD8+ T-cell epitopes from all the hemagglutinin (HA) and neuraminidase (NA) protein sequences available until February 2013 to cover the seasonal as well as the pandemic strains of the H1N1 virus. In the present study, six different immunoinformatics prediction programs were used in order to define the epitopes. Five conserved peptides of HA and six of NA protein were obtained that contained overlapping CD4+ and CD8+ T-cell epitopes. These identified peptides have a binding affinity for a large number of major histocompatibility complex (MHC) alleles. WHGSNRPWVSF of NA protein is a new peptide whose T-cell response has not been previously reported. Population coverage studies have shown that these peptide fragments have the capacity to induce a potent immune response among individuals from different populations around the world. Hence, these HA and NA peptides may be considered as interesting candidates for vaccine design.

Protective immunity to H7N9 influenza viruses elicited by synthetic DNA vaccine

Despite an intensive vaccine program influenza infections remain a major health problem, due to the viruses' ability to change its envelope glycoprotein hemagglutinin (HA), through shift and drift, permitting influenza to escape protection induced by current vaccines or natural immunity. Recently a new variant, H7N9, has emerged in China causing global concern. First, there have been more than 130 laboratory-confirmed human infections resulting in an alarmingly high death rate (32.3%). Second, genetic changes found in H7N9 appear to be associated with enabling avian influenza viruses to spread more effectively in mammals, thus transmitting infections on a larger scale. Currently, no vaccines or drugs are effectively able to target H7N9. Here, we report the rapid development of a synthetic consensus DNA vaccine (pH7HA) to elicit potent protective immunity against the H7N9 viruses. We show that pH7HA induces broad antibody responses that bind to divergent HAs from multiple new members of the H7N9 family. These antibody responses result in high-titer HAI against H7N9. Simultaneously, this vaccine induces potent polyfunctional effector CD4 and CD8T cell memory responses. Animals vaccinated with pH7HA are completely protected from H7N9 virus infection and any morbidity associated with lethal challenge. This study establishes that this synthetic consensus DNA vaccine represents a new tool for targeting emerging infection, and more importantly, its design, testing and development into seed stock for vaccine production in a few days in the pandemic setting has significant implications for the rapid deployment of vaccines protecting against emerging infectious diseases.

A direct and nonredundant role for thymic stromal lymphopoietin on antiviral CD8 T cell responses in the respiratory mucosa

Mucosally produced thymic stromal lymphopoietin (TSLP) regulates Th2 responses by signaling to dendritic cells and CD4 T cells. Activated CD8 T cells express the TSLP receptor (TSLPR), yet a direct role for TSLP in CD8 T cell immunity in the mucosa has not been described. Because TSLP shares signaling components with IL-7, a cytokine important for the development and survival of memory CD8 T cells in systemic infection models, we hypothesized that TSLP spatially and nonredundantly supports the development of these cells in the respiratory tract. In this study, we demonstrate that influenza infection induces the early expression of TSLP by lung epithelial cells with multiple consequences. The global loss of TSLP responsiveness in TSLPR(-/-) mice enhanced morbidity and delayed viral clearance. Using a competitive adoptive transfer system, we demonstrate that selective loss of TSLPR signaling on antiviral CD8 T cells decreases their accumulation specifically in the respiratory tract as early as day 8 after infection, primarily due to a proliferation deficiency. Importantly, the subsequent persistence of memory cells derived from this pool was also qualitatively and quantitatively affected. In this regard, the local support of antiviral CD8 T cells by TSLP is well suited to the mucosa, where responses must be tempered to prevent excessive inflammation. Taken together, these data suggest that TSLP uniquely participates in local immunity in the respiratory tract and modulation of TSLP levels may promote long-term CD8 T cell immunity in the mucosa when other prosurvival signals are limiting.

Interferon regulatory factor 4 sustains CD8(+) T cell expansion and effector differentiation

Upon infection, CD8(+) T cells undergo a stepwise process of early activation, expansion, and differentiation into effector cells. How these phases are transcriptionally regulated is incompletely defined. Here, we report that interferon regulatory factor 4 (IRF4), dispensable for early CD8(+) T cell activation, was vital for sustaining the expansion and effector differentiation of CD8(+) T cells. Mechanistically, IRF4 promoted the expression and function of Blimp1 and T-bet, two transcription factors required for CD8(+) T cell effector differentiation, and simultaneously repressed genes that mediate cell cycle arrest and apoptosis. Selective ablation of Irf4 in peripheral CD8(+) T cells impaired antiviral CD8(+) T cell responses, viral clearance, and CD8(+) T cell-mediated host recovery from influenza infection. IRF4 expression was regulated by T cell receptor (TCR) signaling strength via mammalian target of rapamycin (mTOR). Our data reveal that IRF4 translates differential strength of TCR signaling into different quantitative and qualitative CD8(+) T cell responses.

Does homologous reinfection drive multiple-wave influenza outbreaks? Accounting for immunodynamics in epidemiological models

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We model the primary immune responses to influenza infection in humans.

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We examine the interplay between immunological and epidemiological dynamics.

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The model explains cases of homologous reinfection reported during past pandemics.

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Three epidemic profiles can arise depending on the degree of population mixing.

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A substantial proportion of infected host would remain unprotected after the 2009 influenza pandemic.

Epidemiological models of influenza transmission usually assume that recovered individuals instantly develop a fully protective immunity against the infecting strain. However, recent studies have highlighted host heterogeneity in the development of this immune response, characterized by delay and even absence of protection, that could lead to homologous reinfection (HR). Here, we investigate how these immunological mechanisms at the individual level shape the epidemiological dynamics at the population level. In particular, because HR was observed during the successive waves of past pandemics, we assess its role in driving multiple-wave influenza outbreaks. We develop a novel mechanistic model accounting for host heterogeneity in the immune response. Immunological parameters are inferred by fitting our dynamical model to a two-wave influenza epidemic that occurred on the remote island of Tristan da Cunha (TdC) in 1971, and during which HR occurred in 92 of 284 islanders. We then explore the dynamics predicted by our model for various population settings. We find that our model can explain HR over both short (e.g. week) and long (e.g. month) time-scales, as reported during past pandemics. In particular, our results reveal that the HR wave on TdC was a natural consequence of the exceptional contact configuration and high susceptibility of this small and isolated community. By contrast, in larger, less mixed and partially protected populations, HR alone cannot generate multiple-wave outbreaks. However, in the latter case, we find that a significant proportion of infected hosts would remain unprotected at the end of the pandemic season and should therefore benefit from vaccination. Crucially, we show that failing to account for these unprotected individuals can lead to large underestimation of the magnitude of the first post-pandemic season. These results are relevant in the context of the 2009 A/H1N1 influenza post-pandemic era.

Clinical features and factors associated with outcomes of patients infected with a Novel Influenza A (H7N9) virus: a preliminary study

OBJECTIVE

The present study aimed to analyze clinical features and factors associated with treatment outcomes of H7N9 influenza A virus infection.

METHODS

The clinical progress in 18 H7N9-infected patients was monitored and recorded. The clinical features of H7N9 infection were noted and factors associated with treatment outcomes were analyzed by univariate analyses.

RESULTS

The average ages of patients in recovered and critical conditions were 67.0±10.83 years and 72.75±12.0 years, respectively. Renal insufficiency developed more frequently in critically ill patients (P = 0.023). The duration of traditional Chinese medicine (TCM) therapy was longer in recovered patients than in critically ill patients (P = 0.01). Laboratory tests showed that levels of C-reactive protein, serum creatinine, and myoglobin were significantly higher in critically ill patients than in recovered patients (P = 0.011, 0.04, and 0.016, respectively). Meanwhile, levels of all T cell subsets examined including total CD3(+), CD4(+), CD8(+), and CD45(+) T cells were lower in critically ill patients than in recovered patients (P = 0.033, 0.059, 0.015, and 0.039, respectively). Logistic regression analysis demonstrated that C-reactive protein level, myoglobin level and TCM therapy duration were likely associated with treatment outcomes of H7N9 infection (P = 0.032, 0.041 and 0.017, respectively).

CONCLUSION

Elderly people may have increased risk for H7N9 virus infection. T cell-mediated responses play an important role in defense against the H7N9 virus. C-reactive protein level, myoglobin level and TCM duration may be associated with treatment outcomes of H7N9 infection.

New insights into the aryl hydrocarbon receptor as a modulator of host responses to infection

The host response to infection is known to be influenced by many factors, including genetics, nutritional status, age, as well as drug and chemical exposures. Recent advances reveal that the aryl hydrocarbon receptor (AhR) modulates aspects of the innate and adaptive immune response to viral, bacterial, and parasitic organisms. Although many of these observations were made using the high affinity but poorly metabolized AhR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), not all of the effects are detrimental to the host. Sometimes AhR activation, even with TCDD, was beneficial and improved host resistance and survival. A similar dichotomy is observed in infected AhR-deficient mice, wherein absence of functional AhR sometimes, but not always, alters host resistance. When examined in their totality, current data indicate that AhR controls multiple regulatory pathways that converge with infection-associated signals and depending on the context (e.g., type of pathogen, site of infection), lead to distinct outcomes. This creates numerous exciting opportunities to harness the immunomodulatory action of AhR to transform host responses to infection. Moreover, since many of the mechanisms cued in response to infectious agents are pivotal in the context of other diseases, there is much to be learned about AhR's cellular targets and molecular mechanisms of action.

Increase in IFNγ(-)IL-2(+) cells in recent human CD4 T cell responses to 2009 pandemic H1N1 influenza

Human CD4 T cell recall responses to influenza virus are strongly biased towards Type 1 cytokines, producing IFNγ, IL-2 and TNFα. We have now examined the effector phenotypes of CD4 T cells in more detail, particularly focusing on differences between recent versus long-term, multiply-boosted responses. Peptides spanning the proteome of temporally distinct influenza viruses were distributed into pools enriched for cross-reactivity to different influenza strains, and used to stimulate antigen-specific CD4 T cells representing recent or long-term memory. In the general population, peptides unique to the long-circulating influenza A/New Caledonia/20/99 (H1N1) induced Th1-like responses biased toward the expression of IFNγ(+)TNFα(+) CD4 T cells. In contrast, peptide pools enriched for non-cross-reactive peptides of the pandemic influenza A/California/04/09 (H1N1) induced more IFNγ(-)IL-2(+)TNFα(+) T cells, similar to the IFNγ(-)IL-2(+) non-polarized, primed precursor T cells (Thpp) that are a predominant response to protein vaccination. These results were confirmed in a second study that compared samples taken before the 2009 pandemic to samples taken one month after PCR-confirmed A/California/04/09 infection. There were striking increases in influenza-specific TNFα(+), IFNγ(+), and IL-2(+) cells in the post-infection samples. Importantly, peptides enriched for non-cross-reactive A/California/04/09 specificities induced a higher proportion of Thpp-like IFNγ(-)IL-2(+)TNFα(+) CD4 T cells than peptide pools cross-reactive with previous influenza strains, which induced more Th1 (IFNγ(+)TNFα(+)) responses. These IFNγ(-)IL-2(+)TNFα(+) CD4 T cells may be an important target population for vaccination regimens, as these cells are induced upon infection, may have high proliferative potential, and may play a role in providing future effector cells during subsequent infections.

Pediatric influenza vaccination: understanding the T-cell response

Influenza A virus-specific T cells are highly cross-reactive and contribute to heterosubtypic immunity, which may afford protection against novel pandemic strains of influenza virus. However, the magnitude and nature of virus-specific T-cell responses induced by natural infections and/or vaccination in young children is poorly understood. Host factors, such as the development of the immune system during childhood and environmental factors such as exposure rates to influenza viruses and interference by vaccination contribute to shaping the magnitude and specificity of the T-cell response. Here, the authors review several of these factors, including the differences between T-cell responses of young children and adults, the age-dependent frequency of virus-specific T cells and the impact of annual childhood influenza vaccination. In addition, the authors summarize all currently available studies in which influenza vaccine-induced T-cell responses were evaluated. The authors discuss these findings in the light of developing vaccines and vaccination strategies aiming at the induction of protective immunity to seasonal and pandemic influenza viruses of antigenically distinct subtypes.

Interleukin-7, but not thymic stromal lymphopoietin, plays a key role in the T cell response to influenza A virus

The immune response to viral infection is ideally rapid and specific, resulting in viral clearance and establishment of immune memory. Some viruses such as HIV can evade such responses leading to chronic infection, while others like Influenza A can elicit a severe inflammatory response with immune-related complications including death. Cytokines play a major role in shaping the appropriate outcomes to infection. While Interleukin-7 (IL-7) has a critical role in T and B cell development, treatment with IL-7 has recently been shown to aid the adaptive T cell response in clearance of chronic viral infection. In contrast, the IL-7-related cytokine thymic stromal lymphopoietin (TSLP) has a limited role in lymphocyte development but is important in the immune response to parasitic worms and allergens. The role for these cytokines in the immune response to an acute viral infection is unclear. IL-7 and TSLP share IL-7Rα as part of their heterodimeric receptors with the gamma common chain (γc) and TSLPR, respectively. We investigated the role of IL-7 and TSLP in the primary immune response to influenza A infection using hypomorphic IL-7Rα (IL-7Rα^449F) and TSLPR^−/− mice. We found that IL-7, but not TSLP, plays an important role in control of influenza A virus. We also showed that IL-7 signaling was necessary for the generation of a robust influenza A-specific CD4 and CD8 T cell response and that this requirement is intrinsic to CD8 T cells. These findings demonstrate a significant role for IL-7 during acute viral infection.

Repeated exposure to trace amounts of woodchuck hepadnavirus induces molecularly evident infection and virus-specific T cell response in the absence of serological infection markers and hepatitis

Exposure to multiple small doses of hepatitis B virus (HBV) is a frequent occurrence in high-risk groups, including close relatives of infected individuals, primary care givers, and intravenous drug users. It remains uncertain whether such repeated contact may culminate in a symptomatic infection coinciding with hepatitis in individuals not immunoprotected. In this study, we evaluated consequences of multiple exposures to small, liver-nonpathogenic amounts of infectious hepadnavirus in the woodchuck model of hepatitis B. Virus-naïve animals were intravenously injected with 6 weekly doses of 110 DNase digestion-protected virions of woodchuck hepatitis virus (WHV), injected again with 6 weekly 110-virion doses after 7.5 months, and then challenged or not with a liver-pathogenic dose of 1.1 × 10(6) virions of the same inoculum. The data revealed that two rounds of such repeated exposure did not result in serologically evident infection or hepatitis. However, a low-level WHV DNA-positive infection accompanied by a WHV-specific T cell response in the absence of antiviral antibody reactivity was established. The kinetics of the virus-specific and mitogen-induced (generalized) T cell responses and the inability to induce immunoprotection against challenge with a large, liver-pathogenic virus dose were closely comparable to those previously reported for occult infection initiated by a single liver-nonpathogenic dose of WHV. Thus, repeated exposures to small quantities of hepadnavirus induce molecularly evident but serologically silent infection that does not culminate in hepatitis or generate immune protection. The findings imply that the HBV-specific T cell response encountered in the absence of serological markers of infection likely reflects ongoing occult infection.

Enhanced immune response induced by a potential influenza A vaccine based on branched M2e polypeptides linked to tuftsin

Vaccination is the most effective means for preventing influenza-associated morbidity and mortality. Since the influenza virus mutates frequently, the virus strains for new vaccine production should be changed according to predicted epidemic strains. The extracellular domain of matrix protein 2 (M2e) is 24 amino acids long, which is highly conserved and therefore a good target for the development of a universal vaccine which may protect against a much wider range of influenza A virus strains. However its low antigenicity and immunogenicity, which are related to its small size, poses a big challenge for vaccine development. Multiple antigen peptide system (MAP) is based on an inert core molecule of radially branching lysine dendrites onto which a number of peptide antigens are anchored. Tuftsin is an immuno-stimulant molecule peptide. Here we developed a novel peptide vaccine by connecting a tuftsin to a branched, four-copy M2e. Not only did this increase the molecular mass, but also potentiate the immunogenicity. Two branched peptides, (M2e)4-tuftsin and (M2e)4-G4(tuftsin was replaced with four glycines), and a M2e monomer were synthesized using standard solid-phase methods. In vitro and in vivo studies were performed to compare their antigenicity and immunogenicity. Experiments in BALB/c mice demonstrated that the branched M2e could induce stronger humoral and cellular immune responses than the M2e monomer, and (M2e)4-tuftsin induced stronger humoral and cellular immune response than (M2e)4-G4. After lethal challenge with influenza virus PR8 strain, up to 80% of the animals in the (M2e)4-tuftsin vaccinated group still survived, in contrast to 44% in the (M2e)4-G4 group and 30% in the M2e monomer group. The combination of branched polypeptides and tuftsin in vaccine design is presented here for the first time, and the results show that the new construct is a promising candidate for a universal vaccine against the influenza A virus.