Influenza viruses are enveloped viruses, which belong to the Orthomyxoviridae family with a single-stranded, eight-segmented RNA genome of negative polarity. The viral particles are spherical with approximately 100 nm in diameter, containing helical ribonucleocapsid and four viral envelope proteins (hemagglutinin, HA; neuraminidase, NA; matrix, M1; ion channel, M2). In this study, the influenza virus-like particles (VLPs) were constructed by chimerization of human and avian influenza viral proteins using baculovirus-insect cell expression system. Three types of chimeric VLPs were obtained, including (i) chimerization of HA (A/ Thailand/ 1(KAN-1)/ 2004/ H5N1(clade 1)) and M1 (A/ WSN/ 1933/H1N1) (ii) chimerization of HA (A/ Thailand/ 1(KAN-1)/ 2004/ H5N1 (clade 1)), M1 (A/ WSN/ 1933/ H1N1), NA (A/ Viet Nam/ 1203/ 2004/ H5N1), M2 (A/ WSN/1933/H1N1), and can be further fabricated by replacing HA to that of different H5N1 clades. (iii) generate of fluorescence VLPs (fVLPs) by introducing EGFP to NA and M2 structural proteins, that could use to the cell binding studies by confocal microscopy. All of these chimeric VLPs expressed by baculovirus-infected Sf9 insect cells present a spike signature structure on their VLP surfaces as demonstrated by transmission electronic microscopy (TEM).

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