Immunobiological properties of influenza A (H7N9) hemagglutinin and neuraminidase proteins

Recombinant vaccinia viruses harboring the complete hemagglutinin (HA) or neuraminidase (NA) genes from the influenza A/Anhui/1/2013 (H7N9) virus were constructed (rVac-H7 HA and rVac-N9 NA viruses). The HA and NA proteins were expressed in the cytoplasm and on the plasma membrane of thymidine-kinase-negative (TK^-) cells infected with these recombinant viruses. Only one form of the HA protein was expressed in infected TK^- cells, with a molecular weight (MW) of 75 kDa, but three forms were found when the culture medium was supplemented with trypsin (MWs of 75, 50 and 27 kDa), which was similar to what was found in Madin-Darby canine kidney (MDCK) cells infected with reverse genetic (rg) influenza viruses carrying HA genes of H7N9 virus origin. One form of hyperglycosylated NA protein with a MW of 75 kDa was produced in rVac-N9-NA-virus-infected TK^- or MDCK cells. The MW decreased to 55 kDa after deglycosylation. The hyperglycosylated recombinant NA protein demonstrated sialidase activity in a fetuin-based neuraminidase assay. The rVac-H7 HA and rVac-N9 NA viruses elicited significantly higher anti-HA and anti-NA antibody titers in BALB/c mice that were immunized once than in ICR mice. The anti-HA and anti-NA antibodies showed activity against homosubtypic HA or NA, but not against heterosubtypic HA or NA, as determined by hemagglutination-inhibition and microneutralization assays for anti-HA antibodies and neuraminidase-inhibition and replication-inhibition assays for anti-NA antibodies. Taken together, our data demonstrated immunobiological properties of recombinant HA and NA proteins that might be useful for vaccine development.