Multiple basic amino acids in the cleavage site of H7N9 hemagglutinin contribute to high virulence in mice

Wenjun Song; Xiaofeng Huang; Wenda Guan; Pin Chen; Pui Wang; Min Zheng; Zhengtu Li; Yutao Wang; Zifeng Yang; Honglin Chen; Xinhua Wang

doi:10.21037/jtd-21-226

Multiple basic amino acids in the cleavage site of H7N9 hemagglutinin contribute to high virulence in mice

J Thorac Dis. 2021 Aug;13(8):4650-4660. doi: 10.21037/jtd-21-226.

Authors

Wenjun Song^{1

2}, Xiaofeng Huang², Wenda Guan¹, Pin Chen², Pui Wang², Min Zheng², Zhengtu Li¹, Yutao Wang¹, Zifeng Yang¹, Honglin Chen², Xinhua Wang¹

Affiliations

¹ State Key Laboratory of Respiratory Disease, Institute of Integration of Traditional and Western Medicine, First Affiliated Hospital of Guangzhou Medical University, Guangzhou, China.
² State Key Laboratory for Emerging Infectious Diseases, Department of Microbiology, and the Research Centre of Infection and Immunology, The University of Hong Kong, Hong Kong SAR, China.

Abstract

Background: Avian influenza A (H7N9) virus has caused more than 1,500 cases of human infection since its emergence in early 2013. Displaying little or no pathogenicity in poultry, but a 40% case-fatality rate in humans, five waves of H7N9 human infections occurred in China during 2013-2017, caused solely by a low pathogenicity strain. However, avian isolates possessing a polybasic connecting peptide in the hemagglutinin (HA) protein were detected in mid-2016, indicating that a highly pathogenic virus had emerged and was co-circulating with the low pathogenicity strains.

Methods: Here we characterize the pathogenicity of a newly emerged human H7N9 variant with a PEVPKRKRTAR/GLF insertion motif at the cleavage site of the HA protein in vitro and in vivo.

Results: This variant replicates in MDCK cells independently of TPCK-trypsin, which is indicative of high pathogenicity in chickens. The 50% mouse lethal dose (MLD₅₀) of this novel isolate was less than 10 plaque forming units (PFU), compared with 3.16×10⁴ for an identical virus lacking the polybasic insertion, indicating a high virulence phenotype.

Conclusions: Our results demonstrate that the multiple basic amino acid insertion in the HA protein of the H7N9 variant confers high virulence in mammals, highlighting a potential risk to humans. Continuous viral surveillance is therefore necessary in the China region to improve pandemic preparedness.

Keywords: H7N9; Influenza A virus (IAV); cleavage site; highly pathogenic avian influenza (HPAI); polybasic connecting peptide.