The refinement of the haemagglutinin membrane glycoprotein of influenza virus

The crystal structure of the haemagglutinin glycoprotein, a trimer from the membrane of influenza virus, has been refined at 3.0 Å resolution to an R factor of 20.4%. The first 23 cycles were carried out on coordinates of an averaged monomer determined from a non-crystallographically threefold-symmetry-averaged electron density map. The contribution of structure factors to the least-squares equations were determined from non-crystallographically averaged gradient difference and curvature Fourier maps. The refinement was restrained using the Hendrickson & Konnert algorithm. These initial cycles were followed by 25 cycles of refinement with trigonometric evaluation of the derivatives on the complete trimer (208 422 daltons) on a Cray 1/S. Forty-eight water molecules and portions of five N-linked oligosaccharides were identified

Influenza hemagglutinin stem-fragment immunogen elicits broadly neutralizing antibodies and confers heterologous protection

Influenza hemagglutinin (HA) is the primary target of the humoral response during infection/vaccination. Current influenza vaccines typically fail to elicit/boost broadly neutralizing antibodies (bnAbs), thereby limiting their efficacy. Although several bnAbs bind to the conserved stem domain of HA, focusing the immune response to this conserved stem in the presence of the immunodominant, variable head domain of HA is challenging. We report the design of a thermotolerant, disulfide-free, and trimeric HA stem-fragment immunogen which mimics the native, prefusion conformation of HA and binds conformation specific bnAbs with high affinity. The immunogen elicited bnAbs that neutralized highly divergent group 1 (H1 and H5 subtypes) and 2 (H3 subtype) influenza virus strains in vitro. Stem immunogens designed from unmatched, highly drifted influenza strains conferred robust protection against a lethal heterologous A/Puerto Rico/8/34 virus challenge in vivo. Soluble, bacterial expression of such designed immunogens allows for rapid scale-up during pandemic outbreaks

Changed epitopes drive the antigenic drift for influenza A (H3N2) viruses

<p>Abstract</p> <p>Background</p> <p>In circulating influenza viruses, gradually accumulated mutations on the glycoprotein hemagglutinin (HA), which interacts with infectivity-neutralizing antibodies, lead to the escape of immune system (called antigenic drift). The antibody recognition is highly correlated to the conformation change on the antigenic sites (epitopes), which locate on HA surface. To quantify a changed epitope for escaping from neutralizing antibodies is the basis for the antigenic drift and vaccine development.</p> <p>Results</p> <p>We have developed an epitope-based method to identify the antigenic drift of influenza A utilizing the conformation changes on epitopes. A changed epitope, an antigenic site on HA with an accumulated conformation change to escape from neutralizing antibody, can be considered as a "key feature" for representing the antigenic drift. According to hemagglutination inhibition (HI) assays and HA/antibody complex structures, we statistically measured the conformation change of an epitope by considering the number of critical position mutations with high genetic diversity and antigenic scores. Experimental results show that two critical position mutations can induce the conformation change of an epitope to escape from the antibody recognition. Among five epitopes of HA, epitopes A and B, which are near to the receptor binding site, play a key role for neutralizing antibodies. In addition, two changed epitopes often drive the antigenic drift and can explain the selections of 24 WHO vaccine strains.</p> <p>Conclusions</p> <p>Our method is able to quantify the changed epitopes on HA for predicting the antigenic variants and providing biological insights to the vaccine updates. We believe that our method is robust and useful for studying influenza virus evolution and vaccine development.</p

Mimotope ELISA for Detection of Broad Spectrum Antibody against Avian H5N1 Influenza Virus

Science and Technology Foundation of Fujian Province [2009YZ0002]; National Natural Science Foundation of China [30901077]; National High Technology Research and Development Program [2010AA022801]Background: We have raised a panel of broad spectrum neutralizing monoclonal antibodies against the highly pathogenic H5N1 avian influenza virus, which neutralize the infectivity of, and afford protection against infection by, most of the major genetic groups of the virus evolved since 1997. Peptide mimics reactive with one of these broad spectrum H5N1 neutralizing antibodies, 8H5, were identified from random phage display libraries. Method: The amino acid residues of the most reactive 12mer peptide, p125 (DTPLTTAALRLV), were randomly substituted to improve its mimicry of the natural 8H5 epitope. Result: 133 reactive peptides with unique amino acid sequences were identified from 5 sub-libraries of p125. Four residues (2,4,5.9) of the parental peptide were preserved among all the derived peptides and probably essential for 8H5 binding. These are interspersed among four other residues (1,3,8,10), which exhibit restricted substitution and probably could contribute to binding, and another four (6,7,11,12) which could be randomly substituted and probably are not essential for binding. One peptide, V-1b, derived by substituting 5 of the latter residues is the most reactive and has a binding constant of 3.16x10(-9) M, which is 38 fold higher than the affinity of the parental p125. Immunoassay produced with this peptide is specifically reactive with 8H5 but not also the other related broad spectrum H5N1 avian influenza virus neutralizing antibodies. Serum samples from 29 chickens infected with H5N1 avian influenza virus gave a positive result by this assay and those from 12 uninfected animals gave a negative test result. Conclusion: The immunoassay produced with the 12 mer peptide, V1-b, is specific for the natural 8H5 epitope and can be used for detection of antibody against the broad spectrum neutralization site of H5N1 avian influenza virus

Cross-Protective Potential of a Novel Monoclonal Antibody Directed against Antigenic Site B of the Hemagglutinin of Influenza A Viruses

The hemagglutinin (HA) of influenza A viruses has been classified into sixteen distinct subtypes (H1–H16) to date. The HA subtypes of influenza A viruses are principally defined as serotypes determined by neutralization or hemagglutination inhibition tests using polyclonal antisera to the respective HA subtypes, which have little cross-reactivity to the other HA subtypes. Thus, it is generally believed that the neutralizing antibodies are not broadly cross-reactive among HA subtypes. In this study, we generated a novel monoclonal antibody (MAb) specific to HA, designated MAb S139/1, which showed heterosubtypic cross-reactive neutralization and hemagglutination inhibition of influenza A viruses. This MAb was found to have broad reactivity to many other viruses (H1, H2, H3, H5, H9, and H13 subtypes) in enzyme-linked immunosorbent assays. We further found that MAb S139/1 showed neutralization and hemagglutination-inhibition activities against particular strains of H1, H2, H3, and H13 subtypes of influenza A viruses. Mutant viruses that escaped neutralization by MAb S139/1 were selected from the A/Aichi/2/68 (H3N2), A/Adachi/2/57 (H2N2), and A/WSN/33 (H1N1) strains, and sequence analysis of the HA genes of these escape mutants revealed amino acid substitutions at positions 156, 158, and 193 (H3 numbering). A molecular modeling study showed that these amino acids were located on the globular head of the HA and formed a novel conformational epitope adjacent to the receptor-binding domain of HA. Furthermore, passive immunization of mice with MAb S139/1 provided heterosubtypic protection. These results demonstrate that MAb S139/1 binds to a common antigenic site shared among a variety of HA subtypes and neutralizes viral infectivity in vitro and in vivo by affecting viral attachment to cells. The present study supports the notion that cross-reactive antibodies play some roles in heterosubtypic immunity against influenza A virus infection, and underscores the potential therapeutic utility of cross-reactive antibodies against influenza

Antibody evasion by the N terminus of murid herpesvirus-4 glycoprotein B

Herpesviruses characteristically transmit infection from immune hosts. Although their success in escaping neutralization by pre-formed antibody is indisputable, the underlying molecular mechanisms remain largely unknown. Glycoprotein B (gB) is the most conserved component of the herpesvirus entry machinery and its N terminus (gB-NT) is a common neutralization target. We used murid herpesvirus-4 to determine how gB-NT contributes to the virus–antibody interaction. Deleting gB-NT had no obvious impact on virus replication, but paradoxically increased virion neutralization by immune sera. This reflected greater antibody access to neutralization epitopes on gH/gL, with which gB was associated. gB-NT itself was variably protected against antibody by O-linked glycans; on virions from epithelial cells it was protected almost completely. gB-NT therefore provides a protective and largely protected cover for a vulnerable part of gH/gL. The conservation of predicted glycosylation sites in other mammalian herpesvirus gB-NTs suggests that this evasion mechanism is widespread. Interestingly, the gB-NT glycans that blocked antibody binding could be targeted for neutralization instead by a lectin, suggesting a means of therapeutic counterattack

IgG Fc Receptors Provide an Alternative Infection Route for Murine Gamma-Herpesvirus-68

BACKGROUND: Herpesviruses can be neutralized in vitro but remain infectious in immune hosts. One difference between these settings is the availability of immunoglobulin Fc receptors. The question therefore arises whether a herpesvirus exposed to apparently neutralizing antibody can still infect Fc receptor(+) cells. PRINCIPAL FINDINGS: Immune sera blocked murine gamma-herpesvirus-68 (MHV-68) infection of fibroblasts, but failed to block and even enhanced its infection of macrophages and dendritic cells. Viral glycoprotein-specific monoclonal antibodies also enhanced infection. MHV-68 appeared to be predominantly latent in macrophages regardless of whether Fc receptors were engaged, but the infection was not abortive and new virus production soon overwhelmed infected cultures. Lytically infected macrophages down-regulated MHC class I-restricted antigen presentation, endocytosis and their response to LPS. CONCLUSIONS: IgG Fc receptors limit the neutralization of gamma-herpesviruses such as MHV-68