Identification of a Novel Universal Potential Epitope on the Cytoplasmic Tail of H7N9 Virus Hemagglutinin

Abstract

Dear Editor, H7N9 is a recently identified subtype of influenza A virus that caused a major outbreak in humans in China in 2013. According to the latest data provided by the Chinese Center for Disease Control and Prevention (http://www.moh.gov. cn/zwgk/yqbb3/ejlist.shtml, updated on October 31, 2018), the mortality rate of H7N9 infections in China amounts to 39.7% (611/1536). Thus, H7N9 poses a serious public health threat. Influenza A viruses comprise a group of antigenically diverse pathogens that cause respiratory tract infections in both animal and human populations (Thornburg et al. 2016). Subtypes of influenza A viruses are characterized by their surface glycoproteins, including hemagglutinin (HA) and neuraminidase (NA). HA consists of a globular head region with a receptor-binding pocket and a conserved stem motif (Liu et al. 2016), and mediates the binding of influenza A virus to host cells (Melikyan et al. 1999). After binding, HA can be divided into three domains: an extracellular domain, a transmembrane domain, and a cytoplasmic tail (CT) (Thornburg et al. 2016). More than a dozen of neutralizing epitopes of HA have been identified to date (Shcherbinin et al. 2016), most of which are on the receptor-binding pocket (Whittle et al. 2011) and the stem motif (Dreyfus et al. 2012). However, H7-subtype inactivated virus is a weak inducer of neutralizing antibody compared to H1N1 and H3N2 (Lee et al. 2015), highlighting the necessity of developing novel strategies in vaccine design against H7N9. This study aimed to identify a novel antigenic epitope on H7N9 virus HA 7. In total, 37 patients with H7N9 infection admitted to Shenzhen Third People's Hospital between December 2012 and March 2015 were included in this study. Plasma and peripheral blood mononuclear cells were separated from fresh blood samples and were stored at-80°C. Full-length HA protein [of strain A/Shanghai/02/2013 (H7N9)] was fragmented into 110 peptides (P1-P110). Each peptide contained 15 amino acids (AAs), with a 10-AA overlap between two neighboring peptides. A library of 108 peptides covering the full-length HA 7 was synthesized except for P9 and P18. Plasma samples from 11 H7N9-infected patients were tested for reactivity with the 108 synthetic peptides by peptide microarray ELISA. As shown in Fig. 1A, the OD450 values for P15, P21, P30, P63, P76, P98, and P110 were significantly higher than those for other peptides, suggesting that the patients' plasma strongly reacted with these peptides, which may be candidate epitopes of HA 7. Among the seven candidates, P110 (AA sequence: FICVKNGNMRCTICI), the last 11 AAs of which compose the HA 7-CT, showed the strongest immunoreaction, whereas the specific affinities of serum antibodies to peptides on extracellular and transmembrane domains were lower. Therefore, the HA 7-CT peptide (KNGNMRCTICI) was further investigated in this study.

Induction of cross‐group broadly reactive antibody response by natural H7N9 avian influenza virus infection and immunization with inactivated H7N9 vaccine in chickens

“…Nevertheless, there are limited data on identifying the antigenic epitopes in HA of the H7 subtype AIV, especially on the polyclonal level. Recently, Liu et al., (2019) characterized the antigenic epitopes of H7N9 HA using the plasma samples from 37 H7N9 infected patients and identified a potential universal epitope in the cytoplasmic tail domain of the HA protein based on sequence alignment. However, cross‐reactivity of the plasma samples with different subtypes was not measured in their study.…”