HA gene amino acid mutations contribute to antigenic variation and immune escape of H9N2 influenza virus

Abstract

Based on differences in the amino acid sequence of the protein haemagglutinin (HA), the H9N2 avian influenza virus (H9N2 virus) has been clustered into multiple lineages, and its rapidly ongoing evolution increases the difficulties faced by prevention and control programs. The HA protein, a major antigenic protein, and the amino acid mutations that alter viral antigenicity in particular have always been of interest. Likewise, it has been well documented that some amino acid mutations in HA alter viral antigenicity in the H9N2 virus, but little has been reported regarding how these antibody escape mutations affect antigenic variation. In this study, we were able to identify 15 HA mutations that were potentially relevant to viral antigenic drift, and we also found that a key amino acid mutation, A180V, at position 180 in HA (the numbering for mature H9 HA), the only site of the receptor binding sites that is not conserved, was directly responsible for viral antigenic variation. Moreover, the recombinant virus with alanine to valine substitution at position 180 in HA in the SH/F/98 backbone (rF/HAA180V virus) showed poor cross-reactivity to immune sera from animals immunized with the SH/F/98 (F/98, A180), SD/SS/94 (A180), JS/Y618/12 (T180), and rF/HAA180V (V180) viruses by microneutralization (MN) assay. The A180V substitution in the parent virus caused a significant decrease in cross-MN titres by enhancing the receptor binding activity, but it did not physically prevent antibody (Ab) binding. The strong receptor binding avidity prevented viral release from cells. Moreover, the A180V substitution promoted H9N2 virus escape from an in vitro pAb-neutralizing reaction, which also slightly affected the cross-protection in vivo. Our results suggest that the A180V mutation with a strong receptor binding avidity contributed to the low reactors in MN/HI assays and slightly affected vaccine efficacy but was not directly responsible for immune escape, which suggested that the A180V mutation might play a key role in the process of the adaptive evolution of H9N2 virus.

Experimental Pathogenicity of H9N2 Avian Influenza Viruses Harboring a Tri-Basic Hemagglutinin Cleavage Site in Sonali and Broiler Chickens

“…Coding mutations in HA and NA proteins of the studied H9N2 viral genome confirmed continuing evolution within the G1 lineage. In general, the amino acid mutations at HA and NA proteins are functionally involved in antigenic shift or drift, virulence, binding ligands, viral oligomerization interfaces, escape mutants, creating or removing a potential N-glycosylation site, drug binding or resistance, and other biological properties of the circulating strains [ 28 , 29 ]. However, a significant number of mutations in the currently studied isolates were found in the potential antigenic sites of the HA protein that may alter its antigenic properties and contribute to vaccinal escape ( Table 1 ; Supplementary Table S3 ).…”

Correction: HA gene amino acid mutations contribute to antigenic variation and immune escape of H9N2 influenza virus

“…Following publication of the original article [ 1 ], we have been informed that author Huoying Shi has been incorrectly affiliated.…”

Deciphering the rule of antigen-antibody amino acid interaction

“…In addition, the spike L452R mutation conferred SARS-CoV-2 escape from the immune system ( 25 ). Our findings suggested that Ags were often not recognized by Ab when other residues replaced antigenic residues K, L, or T. Correspondingly, the A180V mutation in the influenza virus promotes the virus to escape from Ab-based immunity ( 26 – 28 ). V483A mutation in SARS-CoV-2 was resistant to some neutralizing antibodies ( 29 ).…”