Hemagglutinin of Influenza A virus subtype H5N1 (H5 HA)

Hemagglutinin (HA) is the primary surface glycoprotein of the Influenza A/H5N1 virus and serves as the critical mediator of viral entry into host cells [1]. It functions by binding to alpha-2,3-linked sialic acid receptors on the host cell surface, followed by a conformational change that triggers the fusion of the viral envelope with the endosomal membrane [2]. In the context of an inactivated split-virion antigen, the HA protein is presented in a non-infectious form to stimulate the host's immune system [3]. This presentation induces the production of neutralizing antibodies, primarily targeting the HA head or stem regions, which provide protection against subsequent infection by blocking viral attachment or fusion [4]. H5N1 is a highly pathogenic avian influenza strain with significant pandemic potential and high mortality rates in humans, making HA a central target for vaccine development and therapeutic antibody research [5]. Current clinical applications involve monovalent adjuvanted vaccines designed to elicit robust immune responses in pre-pandemic or pandemic scenarios [6]. [1] UniProt P03452; [2] PubMed 16410849; [3] NIH/NIAID Vaccine Research; [4] PubMed 23467121; [5] WHO H5N1 Fact Sheet; [6] FDA Audenz Prescribing Information.

Other names

H5N1 HemagglutininHA proteinH5 antigenInfluenza A virus (A/H5N1) hemagglutininHemagglutinin [Influenza A virus]

The inactivated split-virion antigen acts as an immunogen that triggers B-cell activation and the subsequent production of polyclonal antibodies. These antibodies specifically target the hemagglutinin (HA) protein, neutralizing the virus by sterically hindering its binding to host sialic acid receptors or by preventing the pH-dependent conformational change required for membrane fusion [1][4].