Influenza A virus Hemagglutinin (H3) (HA) (HA)

Influenza A H3 hemagglutinin is a homotrimeric surface glycoprotein essential for the entry of H3N2 influenza viruses into host cells. It functions by binding to terminal sialic acids on host cell surface glycoproteins and glycolipids, triggering receptor-mediated endocytosis (Gamblin & Skehel, 2010). Once inside the acidic environment of the endosome, the hemagglutinin undergoes a massive structural rearrangement to facilitate the fusion of the viral and endosomal membranes, releasing the viral genome into the cytoplasm (Blaas et al., 2013). The A/Singapore/INFIMH-16-0019/2016 strain was a significant H3N2 variant selected by the World Health Organization for inclusion in the 2018-2019 influenza vaccines due to its prevalence and antigenic characteristics (WHO, 2017). Hemagglutinin is the primary target for neutralizing antibodies induced by vaccination and is the focus of drug development efforts, such as fusion inhibitors like Umifenovir and various experimental monoclonal antibodies (Boriskin et al., 2008). However, the protein's high rate of antigenic drift necessitates continuous surveillance and frequent vaccine updates to maintain protective efficacy.

Other names

H3 hemagglutininHemagglutinin H3 subtypeHA proteinA/Singapore/INFIMH-16-0019/2016(H3N2) Hemagglutinin

Inhibition of viral attachment to host sialic acid receptors and prevention of pH-dependent membrane fusion within the endosome (Blaas et al., 2013; Boriskin et al., 2008).