Glycomic analysis of host response reveals high mannose as a key mediator of influenza severity.

Influenza virus infections cause a wide variety of outcomes, from mild disease to 3 to 5 million cases of severe illness and ∼290,000 to 645,000 deaths annually worldwide. The molecular mechanisms underlying these disparate outcomes are currently unknown. Glycosylation within the human host plays a critical role in influenza virus biology. However, the impact these modifications have on the severity of influenza disease has not been examined. Herein, we profile the glycomic host responses to influenza virus infection as a function of disease severity using a ferret model and our lectin microarray technology. We identify the glycan epitope high mannose as a marker of influenza virus-induced pathogenesis and severity of disease outcome. Induction of high mannose is dependent upon the unfolded protein response (UPR) pathway, a pathway previously shown to associate with lung damage and severity of influenza virus infection. Also, the mannan-binding lectin (MBL2), an innate immune lectin that negatively impacts influenza outcomes, recognizes influenza virus-infected cells in a high mannose-dependent manner. Together, our data argue that the high mannose motif is an infection-associated molecular pattern on host cells that may guide immune responses leading to the concomitant damage associated with severity.

Age-Related Pathology Associated with H1N1 A/California/07/2009 Influenza Virus Infection.

Influenza virus infection causes a spectrum of diseases, ranging from mild upper respiratory tract infection to severe lower respiratory tract infection, that can lead to diffuse alveolar damage, interstitial and airspace inflammation, or acute respiratory failure. Mechanisms instructing disease severity are not completely understood, but host, viral, and bacterial factors influence disease outcome. With age being one host factor associated with a higher risk of severe influenza, we investigated regional pulmonary distribution and severity of pneumonia after 2009 H1N1 influenza virus infection in newly weaned, adult, and aged ferrets to better understand age-dependent susceptibility and pathology. Aged ferrets exhibited greater weight loss and higher rates of mortality than adult ferrets, whereas most newly weaned ferrets did not lose weight but had a lack of weight gain. Newly weaned ferrets exhibited minimal pneumonia, whereas adult and aged ferrets had a spectrum of pneumonia severity. Influenza virus-induced pneumonia peaked earliest in adult ferrets, whereas aged ferrets had delayed presentation. Bronchial severity differed among groups, but bronchial pathology was comparable among all cohorts. Alveolar infection was strikingly different among groups. Newly weaned ferrets had little alveolar cell infection. Adult and aged ferrets had alveolar infection, but aged ferrets were unable to clear infection. These different age-related pneumonia and infection patterns suggest therapeutic strategies to treat influenza should be tailored contingent on age.

Sex disparities in influenza: A multiscale network analysis.

Sex differences in the pathogenesis of infectious diseases because of differential immune responses between females and males have been well-documented for multiple pathogens. However, the molecular mechanism underlying the observed sex differences in influenza virus infection remains poorly understood. In this study, we used a network-based approach to characterize the blood transcriptome collected over the course of infection with influenza A virus from female and male ferrets to dissect sex-biased gene expression. We identified significant differences in the temporal dynamics and regulation of immune responses between females and males. Our results elucidate sex-differentiated pathways involved in the unfolded protein response (UPR), lipid metabolism, and inflammatory responses, including a female-biased IRE1/XBP1 activation and male-biased crosstalk between metabolic reprogramming and IL-1 and AP-1 pathways. Overall, our study provides molecular insights into sex differences in transcriptional regulation of immune responses and contributes to a better understanding of sex biases in influenza pathogenesis.

Impact of diabetes status on immunogenicity of trivalent inactivated influenza vaccine in older adults.

Individuals with type 2 diabetes mellitus experience high rates of influenza virus infection and complications. We compared the magnitude and duration of serologic response to trivalent influenza vaccine in adults aged 50-80 with and without type 2 diabetes mellitus. Serologic response to influenza vaccination was similar in both groups: greater fold-increases in antibody titer occurred among participants with lower pre-vaccination antibody titers. Waning of antibody titers was not influenced by diabetes status.

Common and species-specific molecular signatures, networks, and regulators of influenza virus infection in mice, ferrets, and humans.

Molecular responses to influenza A virus (IAV) infections vary between mammalian species. To identify conserved and species-specific molecular responses, we perform a comparative study of transcriptomic data derived from blood cells, primary epithelial cells, and lung tissues collected from IAV-infected humans, ferrets, and mice. The molecular responses in the human host have unique functions such as antigen processing that are not observed in mice or ferrets. Highly conserved gene coexpression modules across the three species are enriched for IAV infection-induced pathways including cell cycle and interferon (IFN) signaling. TDRD7 is predicted as an IFN-inducible host factor that is up-regulated upon IAV infection in the three species. TDRD7 is required for antiviral IFN response, potentially modulating IFN signaling via the JAK/STAT/IRF9 pathway. Identification of the common and species-specific molecular signatures, networks, and regulators of IAV infection provides insights into host-defense mechanisms and will facilitate the development of novel therapeutic interventions against IAV infection.

The effect of frailty on HAI response to influenza vaccine among community-dwelling adults ≥ 50 years of age.

The immune response to vaccine antigens is less robust in older adults because of changes in the aging immune system. Frailty, the multi-dimensional syndrome marked by losses in function and physiological reserve, is increasingly prevalent with advancing age. Frailty accelerates this immunosenescence but the consequence of frailty on immune response specific to influenza vaccine among older adults, is mixed. An observational, prospective study of 114 adults was conducted in the fall of 2013 to assess the association of physical frailty with immune response to standard dose influenza vaccine in community-dwelling adults ≥ 50 years of age. Participants were stratified by age (<65 years and ≥65 years), and vaccine strain (Influenza A/H1N1, A/H3N2 and B) was analyzed separately adjusting for body mass index (BMI) and baseline log2 hemagglutination inhibition (HAI) titers. Overall, immune responses were lower among those ≥65 years of age than those <65 years. Among those ≥65 years there were no significant differences between frail and non-frail individuals in seroprotection or seroconversion for any influenza strain. Frail individuals <65 years of age compared with non-frail individuals were more likely to be seroprotected and to seroconvert post vaccination. Linear regression models show the same pattern of significant differences between frail and non-frail for those <65 years but no significant differences between frailty groups for those ≥65 years. Additional research may elucidate the reasons for the differences observed between younger frail and non-frail adults.

Molecular-level analysis of the serum antibody repertoire in young adults before and after seasonal influenza vaccination.

Molecular understanding of serological immunity to influenza has been confounded by the complexity of the polyclonal antibody response in humans. Here we used high-resolution proteomics analysis of immunoglobulin (referred to as Ig-seq) coupled with high-throughput sequencing of transcripts encoding B cell receptors (BCR-seq) to quantitatively determine the antibody repertoire at the individual clonotype level in the sera of young adults before and after vaccination with trivalent seasonal influenza vaccine. The serum repertoire comprised between 40 and 147 clonotypes that were specific to each of the three monovalent components of the trivalent influenza vaccine, with boosted pre-existing clonotypes accounting for ∼60% of the response. An unexpectedly high fraction of serum antibodies recognized both the H1 and H3 monovalent vaccines. Recombinant versions of these H1 + H3 cross-reactive antibodies showed broad binding to hemagglutinins (HAs) from previously circulating virus strains; several of these antibodies, which were prevalent in the serum of multiple donors, recognized the same conserved epitope in the HA head domain. Although the HA-head-specific H1 + H3 antibodies did not show neutralization activity in vitro, they protected mice against infection with the H1N1 and H3N2 virus strains when administered before or after challenge. Collectively, our data reveal unanticipated insights regarding the serological response to influenza vaccination and raise questions about the added benefits of using a quadrivalent vaccine instead of a trivalent vaccine.