Influenza D virus: a potential threat for humans?

Influenza D virus (IDV) is a novel influenza virus first isolated from swine in 2011 in Oklahoma. Several studies have isolated IDV in cattle from multiple geographic areas, suggesting that cattle could be a possible primary natural reservoir for the virus. To date, few studies have been performed on human samples and there is no conclusive evidence that IDV has the ability to infect humans. This serological study aimed to assess the prevalence of antibodies against IDV in the human population. The IDV used in the serological analysis was influenza D/bovine/Oklahoma/660/2013. The human serum samples, collected in Italy between 2005 and 2017, were randomly selected from the laboratory serum bank and tested by the haemagglutination inhibition (HI) assay. HI positivity has been confirmed using the virus neutralization (VN) assay. Based on HI positivity (HI titers ≥ 10), a low prevalence (5%–10%) was observed between 2005 and 2007. There has been a sharp increase since 2008, resulting in two main peaks in 2009–2010 and 2013–2014, a finding confirmed by the statistical trend analysis. The same pattern and trends can be seen with higher HI titers of >20 and ≥40. The prevalence of antibodies against IDV has increased in the human population in Italy from 2005 to 2017. Low prevalence values between 2005 and 2007 suggest that IDV most probably circulated before its detection in 2011, and perhaps even before 2005. In Italy, IDV has been shown to circulate among swine and bovine herds. It is, therefore, possible that prevalence peaks in humans follow the infection epidemics in animals and do not to persist in the population, resembling a spillover event from the animal reservoir and showing that the virus may not circulate consistently in the human population. However, IDV seemed to have the ability to elicit an immune response in humans

The study of antibody responses to influenza neuraminidase using a lentiviral pseudotype based ELLA

Influenza pseudotypes represent an alternative to wild type virus for serological assays. To date, pseudotypes (PV) have predominantly been used as surrogates for wild type viruses in microneutralisation assays, where the surface glycoprotein of interest and a reporter gene (such as Luciferase) are used to assess if virus entry into target cells could be inhibited by serum antibodies. The influenza neuraminidase (NA) has the ability to bud and release new virions with or without the contribution of Haemagglutinin (HA). Influenza pseudotypes expressing NA alone, or with HA, were produced to evaluate the antibody response against NA using the enzyme-linked lectin assay (ELLA). The expression of an avian HA with human NAs has enabled the detection of specific antibody reponses against the human circulating subtypes of NA. Within this study a PV-based ELLA assay has been investigated with a pilot panel of sera prepared for an international CONSISE study. Preliminary results have confirmed that the assay is sensitive and could potentially represent a valid alternative to the classical ELLA assay, which requires the employment of reassortant viruses

A Lentiviral Pseudotype ELLA for the Measurement of Antibodies Against Influenza Neuraminidase

Fully detailed pseudotype virus ELLA protocol for measuring antibody responses against influenza neuraminidase

H1N1 viral proteome peptide microarray predicts individuals at risk for H1N1 infection and segregates infection versus pandemrix(®) -vaccination

A high content peptide microarray containing the entire Influenza A virus (A/California/08/2009(H1N1)) proteome and hemagglutinin proteins from 12 other influenza A subtypes, including the hemagglutinin from the (A/South Carolina/1/1918(H1N1)) strain, was used to gauge serum IgG epitope signatures prior to and after pandemrix vaccination/ or H1N1 infection in a Swedish cohort during the pandemic influenza season 2009. A very narrow pattern of pandemic flu specific IgG epitope recognition was observed in the serum from individuals who later contracted H1N1 infection. Moreover the pandemic influenza infection generated IgG reactivity to two adjacent epitopes of the neuraminidase protein. The differential serum IgG recognition was focused on hemagglutinin 1 (H1) and restricted to classical antigenic sites (Cb) in both the vaccinated controls and individuals with flu infections. We further identified a novel epitope VEPGDKITFEATGNL on the Ca antigenic site (251-265) of the Pandemic flu hemagglutinin, which was exclusively recognized in serum from individuals with previous vaccinations and never in serum from individuals with H1N1 infection (confirmed by RNA PCR analysis from nasal swabs). This epitope was mapped to the receptor-binding domain of the influenza hemagglutinin (HA) and could serve as a correlate of immune protection in the context of pandemic flu. The study shows that unbiased epitope mapping using peptide microarray technology leads to the identification of biologically and clinically relevant target structures, it also shows that H1N1 infection induced a different footprint of IgG epitope recognition patterns as compared to the pandemic H1N1 vaccine. This article is protected by copyright. All rights reserved

Serologically-Based Evaluation of Cross-Protection Antibody Responses among Different A(H1N1) Influenza Strains

After the influenza H1N1 pandemic of 2009, the seasonal A/Brisbane/59/2007 strain was replaced by the A/California/07/2009 strain for the influenza virus vaccine composition. After several seasons with no indications on the occurrence of antigenic drift, A/Michigan/45/2015 was chosen as the H1N1 vaccine strain for the 2017/2018 season. Since the immune response to influenza is shaped by the history of exposure to antigenically similar strains, the potential cross-protection between seasonal human influenza vaccine strains and the emerging pandemic strains was investigated. Human serum samples were tested by hemagglutination inhibition and single radial hemolysis assays against A/Brisbane/59/2007, A/California/07/2009, and A/Michigan/45/2015 strains. Strong cross-reactions between A/California/07/2009 and A/Michigan/45/2015 strains were observed in 2009/2010, most likely induced by the start of the 2009 pandemic, and the subsequent post-pandemic seasons from 2010/2011 onward when A/California/07/2009 became the predominant strain. In the 2014/2015 season, population immunity against A/California/07/2009 and A/Michigan/45/2015 strains increased again, associated with strong cross-reactions. Whereas hemagglutination inhibition assay has a higher sensitivity for detection of new seasonal drift, the single radial hemolysis assay is an excellent tool for determining the presence of pre-existing immunity, allowing a potential prediction on the booster potential of influenza vaccines against newly emerging drifted strains. © 2020 by the authors. Licensee MDPI, Basel, Switzerland