Rescue of influenza A virus from recombinant DNA

Rescue of influenza A virus from recombinant DNA. the loss of replication, virulence, and transmissibility associated with the presence of the N-linked glycans. Our findings suggest that the polymorphism in H1 HA at position 147 modulates viral fitness by buffering the constraints caused by N-linked glycans and provide insights into the evolution dynamics of influenza viruses with implications in vaccine immunogenicity. INTRODUCTION Influenza A virus (IAV) causes a serious public health problem. The virus is endemic in the human population and circulates globally, causing seasonal epidemics that result in the deaths of up to half a million people each year (1). Occasionally, a large antigenic shift occurs in IAV, resulting in an influenza pandemic, which can threaten the lives of millions (2). The first pandemic of the 21st century was caused by an H1N1 subtype of IAV in 2009 2009 (2009 H1N1) (3, 4). The hemagglutinin (HA) of this virus was antigenically distinct from the previously circulating PD318088 seasonal human H1N1 (hH1N1) viruses (5C7) and resembled that of swine-lineage H1N1 viruses (8). Based on a structural analysis, the HA epitopes of the 2009 2009 H1N1 virus appeared to be similar to those of the 1918 H1N1 Spanish Flu virus, which caused one of the largest known pandemics and is the evolutionary ancestor of human- and swine-lineage H1N1 viruses (9C11). Another similarity between the two pandemic viruses is the absence of N-linked glycosylation (NLG) at the globular head of HA (12, 13). These features of the 2009 2009 H1N1 virus explained why antibodies that protected against infection SHH with the 2009 2009 H1N1 virus were detected in the elderly who had experienced the 1918 pandemic and in people who had been vaccinated against the swine flu in 1976 (5, 6, 14). During evolution in humans, IAV accumulates genetic mutations at the antigenic sites of HA that circumvent preexisting immunity, a process PD318088 known as antigenic drift (15). Some of these mutations result in variations in the glycosylation state of the HA associated with changes in viral antigenicity (16) and with immune evasion (17). Since 1918, hH1N1 viruses have acquired multiple NLGs, which PD318088 occur at asparagine (N) residues in accessible N-Xaa-S/T (Xaa, any amino acid except proline) sequons, in the top, side, and stem regions of HA (12, 18). However, HA is neither hyperglycosylated (19) nor glycosylated at random sites (20). Using the HA amino acid sequences of hH1N1 viruses that were available from influenza virus database of the National Centers for Biotechnology Information (NCBI), we compared the NLG patterns in the head region of these HAs. As noted previously (12), we found that various combinations of NLG using only five glycosites (asparagines at 142, 144, 172, 177, and 179 of HA; H1 numbering was applied in the present study unless otherwise specified) have been utilized by hH1N1 viruses (Table 1). In the 1930s, a single NLG at residues 142, 144, or 179 was placed in the HA of hH1N1 viruses. From 1942 to 1985, hH1N1 viruses maintained several combinations of NLGs at residues 144, 172, 177, and/or 179; residue 179 was utilized mostly until 1948. In 1986, hH1N1 viruses exhibited a double mutation, K142N and N144S/T, which allowed a glycan shift from residue 144 to residue 142. The NLGs at residues 142 and 177 then became the NLG signature of hH1N1 viruses until the sugar-free HA head was observed in the 2009 2009 H1N1 viruses (Table 1) PD318088 (21). Table 1 Combinations of NLG sites and the genetic signature at residue 147.