Tetrameric Neuraminidase of Influenza A Virus Is Required to Induce Protective Antibody Responses in Mice.

Xiren Deng,Mei Liu,Qinwen Zheng,Fan Wu,Jinghe Huang,Qimin Wang

doi:10.3389/fmicb.2021.729914

Abstract

Influenza neuraminidase (NA) is able to induce cross-subtype immunity and is considered as a promising target for the development of universal influenza vaccines. However, commercial influenza vaccines only induced low NA-specific immune responses due to the low amounts and the denatured conformation of NA proteins in current inactivated or split influenza vaccines. Here we investigated the protective efficacy of recombinant tetrameric and monomeric NA proteins to determine whether the conformation contributed to induce protective immunity. We found that H1N1PR8NA tetramer (NAtet) could provide complete homologous protection against A/PR8 (H1N1) virus infection in mice, while the protection of H1N1PR8NA monomer (NAmono) was moderate. Higher levels of NA-reactive binding and inhibition antibodies and less weight loss were observed in the H1N1PR8NAtet-vaccinated group. Similarly, H5N1VNNAtet immunization exhibited a preferable heterologous protection than H5N1VNNAmono, but neither H7N9SHNAtet nor H7N9SHNAmono vaccination showed heterosubtypic protection. We also compared the effect of three adjuvants, aluminum, 3′3′-cGAMP (cGAMP), and Poly(I:C), on the humoral response and protective efficacy induced by H1N1PR8NAtet. H1N1PR8NAtet protein adjuvanted with aluminum was observed to exhibited better capacity in inducing NA-specific humoral immunity and preventing weight loss than with cGAMP or Poly(I:C). In conclusion, our data demonstrate that tetrameric NA with natural conformation is required to induce protective anti-NA immunity. The NA tetramer could provide homologous protection and subtype-specific cross-protection. In addition, the aluminum adjuvant is preferable in recombinant NA protein vaccination.

Highlights

The seasonal epidemics and less frequently global pandemics of influenza viruses result in high morbidity and mortality every year
The bands of NA tetramers stabilized by the vasodilator stimulating phosphoprotein (VASP) domain were observed as monomers on Western blotting (Figure 1A), while they showed bands consistent with tetramers when cross-linked (Figure 1C)
These results suggest that the enzymatic activity depends on the tetrameric conformation of the NA proteins

Summary

Introduction

The seasonal epidemics and less frequently global pandemics of influenza viruses result in high morbidity and mortality every year. Vaccination is the most effective way to prevent influenza circulation. The currently licensed vaccines, including inactivated and attenuated influenza vaccines, induce protection mainly by eliciting neutralizing antibodies (NAbs) against the major. Vaccine efficacy depends on the antigenic similarities of HA proteins between the vaccine and circulating strains. The continuous and extensive antigenic variation of HA protein allows influenza viruses to escape from the protection of vaccines. The vaccine components need to be updated yearly based on the prediction of circulating influenza strains. The mismatch of vaccine and circulating strains, as in the 2009–2010 and 2017–2018 influenza seasons, resulted in a significant increase of influenza-related morbidity and mortality. A universal vaccine may overcome the shortage of the current influenza vaccines and provide crossprotection against multiple influenza subtypes

Methods

Results

Conclusion