Equatorial ionization anomaly response to lunar phase and stratospheric sudden warming.

This study examines the ionosphere response to gravitational forces of the lunar phase and dynamical disturbances of the stratospheric sudden warmings (SSWs). The total electron content (TEC) of global ionosphere maps is employed to examine responses of the equatorial ionization anomaly (EIA) crests to lunar phases and twelve SSW events during 2000-2013. The most prominent feature in the ionosphere is the EIA, characterized by two enhanced TEC crests at low latitudes straddling the magnetic equator, which can be used to observe ionospheric plasma dynamics and structures. Results show that the EIA crest appearance time on new/full moons (first/third quarters) leads (lags) that of the overall 14-year average, which causes a pattern of TEC morning enhancements (suppressions) and afternoon suppressions (enhancements). A statistical analysis shows that SSWs can also significantly cause the early appearance of EIA crests, regardless of the lunar phase. Thus, both lunar phase and SSWs can significantly modulate the appearance time of EIA crest and ionospheric plasma dynamics and structures.

Glycosylation at hemagglutinin Asn-167 protects the H6N1 avian influenza virus from tryptic cleavage at Arg-201 and maintains the viral infectivity.

Cleavage of the hemagglutinin (HA) precursor (HA0) by trypsin, which produces the active HA1 and HA2 complex, is a critical step for activating the avian influenza virus (AIV). However, other tryptic cleavage sites on HA might also cause HA degradation and affect the virulence. Otherwise, HA is modified by glycosylation in the host cell. The conjugated glycans on HA may hinder the antigenic epitopes, and thus prevent the virus from being recognized and attacked by the antibodies. In this study, we observed that glycosylation at the Asn-167 (N167) site on the HA1 of the H6N1 AIV strain A/chicken/Taiwan/2838V/00 (2838V) protected Arg-201 (R201) from tryptic cleavage. The 2838V HA protein became sensitive to tryptic cleavage, whereas the glycans at N167 were removed by N-glycosidase F (PNGase-F). Furthermore, the infectivity of 2838V decreased when pretreated with PNGase-F and trypsin. Our observations suggest that the inaccessibility of the R201 residue of HA1 for tryptic cleavage, which is sterically hindered by glycosylation at N167, is a crucial factor for determining the infectivity of the AIV.

Preparation of monoclonal antibodies against poor immunogenic avian influenza virus proteins.

This study established a novel method of pre-screening peptides for monoclonal antibody (mAb) production. Whole virus particles were used as antigens to produce mAbs in the first stage. However, most mAbs obtained from this method were aimed toward hemagglutinin. For this reason, synthetic peptides were used as antigens for mAb production that aimed at the AIV proteins with low abundance or poor immunogenicity in the virus particle. The peptides that showed high immunogenicity were designed using bioinformatic tools for immunization. For high-throughput, a rabbit was used to screen the immunogenicities of the synthetic peptides. Those showed high immunity were used for mAb preparation in mice. Several new mAbs against PB2, PA, M1, M2, NS1 and NS2 proteins were successfully obtained in this study. Furthermore, the epitopes of M1 and NS1 mAbs were determined using competitive western blot assay and competitive ELISA. This study might simplify the mAb preparation and serves as the basis for developing mAb against poor immunogenic proteins.

Antigen-capture enzyme-linked immunosorbent assays for detection of different H5 avian Influenza A virus.

Avian Influenza A virus (AIV) subtype H5 is divided into American and Eurasian lineages, according to hemagglutinin gene sequences. Although methods for detecting H5 AIVs have been described, no H5 strain-specific detection method has been reported. The purpose of the present study was to develop an antigen-capture enzyme-linked immunosorbent assay (ACE) to detect and differentiate between the American and the Eurasian H5 AIVs. Monoclonal antibodies (mAbs) against the HA fragment of a Eurasian H5N2 AIV were used as the capture antibodies as well as the detector antibodies after labeling with horseradish peroxidase to develop an ACE. One mAb was selected for detecting the American as well as the Eurasian H5 AIVs. The other mAb was used for detecting only the Eurasian H5N2 but not the American H5N2 AIVs, H6N1 AIVs, or Newcastle disease virus. The ACEs developed would be useful for detection and differentiation of H5 AIVs from the Eurasian and the American H5 AIVs.