1a.Objectives (from AD-416):
1. Utilize cross-hemagglutination inhibition (HI) assays and antigenic cartography to determine the antigenic relatedness among U.S. swine isolates and between swine isolates from other regions and influenza A viruses from other host species.
2. Determine if antigenic cartography is a predictor of cross-protection for vaccine strain selection in swine.
1b.Approach (from AD-416):
Characterization of influenza A viruses (IAV) circulating in pigs and other non-human mammals has been chronically underfunded and virtually nonexistent in many areas of the world. Antigenic characterization is critical for understanding the evolution of IAV in swine as well as the effectiveness of diagnostic serologic assays and vaccines. Antigenic cartography is a computational tool which calculates antigenic distances between all pairs of viruses and anti-sera included in the HI analysis and plots the distances in a 2- or 3-dimensional grid. Antigenic distances measured in the HI assay and visualized by antigenic cartography with pig hyper-immune sera will be compared to antigenic distance measurements from other types of anti-sera such as convalescent swine sera, ferret sera, or other potential reference sera. The antigenic distances will be used to monitor antigenic evolution or drift in viruses from the U.S. and worldwide as part of ARS-NADC in-house objectives as well as a member of the OFFLU global SIV network. If the swine hyper-immune sera immunologically characterizes the antigenic differences between strains in a similar manner to comparitive reference sera, we will use the hyper-immune sera to quantify the antigenic relationships among swine influenza virus strains in the US and worldwide relative to vaccine strains using HI paired with antigenic cartography. Viruses will be selected based on their antigenic distances in the antigenic map for evaluation in experimental vaccines in in vivo efficacy and cross-protection studies to be conducted at NADC.
Using hemagglutination inhibition (HI) data generated at NADC as part of this initiative, we made antigenic maps for H1N1, H1N2 and H3N2 subtype influenza A viruses circulating in North American pigs to visualize and quantify antigenic diversity among viruses that demonstrate diversity in the hemagglutinin (HA) gene. By integrating the antigenic and genetic evolutionary analyses we defined the molecular basis for antigenic differences among swine influenza A viruses and the antigenic difference between these viruses and currently circulating human seasonal influenza A viruses. By networking with other international swine influenza A virus researchers we have improved global surveillance for influenza in pigs. By incorporating the work within this project into a more global initiative we will quantify the antigenic variation of influenza A viruses in pigs amongst geographic regions, more accurately evaluate the potential for improving vaccine strain selection, and thus better inform the relative risk to both animal and human health from influenza A viruses.
Recently, we used HI assay data generated at NADC for swine and human H3N2 viruses and antigenic cartography to quantify the antigenic differences among H3N2 viruses isolated from pigs in North America from 2006-2012 and current human seasonal influenza A strains. We showed that the swine viruses group into two distinct antigenic clusters according to the phylogenetic cluster to which it belongs. Additionally, we identified a single amino acid substitution was likely responsible for the antigenic differences among clusters. Manuscripts focusing on H1 and H3 viruses are in progress.