Hemagglutination Antigen
Overview
Hemagglutination Antigen (HA) is a surface glycoprotein critical for the infectivity of influenza viruses and other enveloped viruses. It mediates viral attachment to host cells by binding to sialic acid receptors, followed by membrane fusion. HA is classified into 18 subtypes (H1-H18) in influenza A viruses, with H1, H2, and H3 being historically significant in human pandemics. The protein's name derives from its ability to agglutinate red blood cells (hemagglutination), a property exploited in diagnostic assays. As the primary target of neutralizing antibodies, HA is the central component of seasonal influenza vaccines. Recent advances in structural biology have enabled the design of universal vaccines targeting conserved regions of HA.
Physical and Chemical Properties
HA antigens are trimeric proteins with each monomer consisting of two subunits (HA1 and HA2) linked by disulfide bonds. The molecular weight ranges between 75-80 kDa depending on glycosylation patterns. Native HA exists as a membrane-bound form on virions or as soluble recombinant variants produced in insect or mammalian cell systems. Biochemically, HA is sensitive to pH changes—undergoing irreversible conformational changes at acidic pH (5.0-5.5) during viral entry. The receptor-binding site (RBS) in the globular head domain shows high variability, while the stalk domain contains more conserved epitopes. Glycosylation at asparagine residues affects antigenicity and immune evasion.
Main Applications
1. Vaccine Development: HA is the principal component of inactivated and recombinant influenza vaccines. Seasonal vaccines contain HA from 3-4 circulating strains as recommended by WHO. 2. Diagnostic Testing: Hemagglutination inhibition (HI) assays measure antibody titers against specific HA subtypes. Rapid antigen tests detect HA in clinical specimens. 3. Virology Research: Used to study viral entry mechanisms, antigenic drift, and host adaptation. Emerging applications include nanoparticle-based vaccines displaying multimeric HA and glycan microarray analysis to map receptor specificity. In biotech, HA tags (YPYDVPDYA peptide derived from influenza HA) are widely used for protein purification and detection.
Safety and Storage
HA antigens derived from pathogenic strains require Biosafety Level 2 (BSL-2) handling. Inactivated antigens should be confirmed for absence of live virus via plaque assays. Personnel must use gloves, lab coats, and eye protection when working with lyophilized or liquid formulations. For storage, lyophilized HA is stable for years at -20°C when desiccated. Reconstituted solutions should be aliquoted to avoid repeated freeze-thaw cycles (stable for weeks at 4°C with protease inhibitors). Shipping typically requires dry ice for international transport, complying with IATA regulations for biological substances.
B2B Procurement Guide
When sourcing HA antigens, specify: 1. Viral strain (e.g., A/Victoria/2570/2019 H1N1) and clade; 2. Production system (egg-derived, cell culture, recombinant); 3. Purity level (≥90% for immunoassays, ≥95% for structural studies); 4. Endotoxin limits (critical for in vivo use). Leading suppliers include Sino Biological, Sigma-Aldrich, and native antigen companies. Bulk purchases (10+ mg) often qualify for 15-30% discounts. For GMP-grade HA (vaccine production), expect lead times of 3-6 months. Always request Certificate of Analysis with SDS-PAGE, HI activity, and sterility testing data.