Hepatitis B surface antigen (HBsAg) (HBsAg)

The Hepatitis B surface antigen (HBsAg) "a" determinant is a critical, highly conserved conformational epitope located within the major hydrophilic region (MHR) of the HBsAg protein, typically spanning amino acid residues 124 to 147 (Cooreman et al., 2001, Journal of Biomedical Science). This epitope is the primary target for neutralizing antibodies (anti-HBs) produced during natural infection or induced by vaccination, making it the central component of global Hepatitis B prevention strategies (Lazarevic, 2014, World Journal of Gastroenterology). The structural integrity of the "a" determinant is essential for the virus to interact with the sodium taurocholate cotransporting polypeptide (NTCP) receptor on human hepatocytes, which facilitates viral entry and subsequent infection (Yan et al., 2012, eLife). In therapeutic contexts, recombinant HBsAg is the active ingredient in vaccines like Engerix-B and Heplisav-B, while Hepatitis B immunoglobulin (HBIG) provides passive immunity by binding directly to this determinant (CDC, 2023; Shouval, 2003, Journal of Hepatology). However, mutations within this region, most notably the G145R substitution, can lead to "vaccine escape" or "diagnostic escape," where the virus evades immune detection or standard screening assays (Carman et al., 1990, Lancet). Modern drug development, such as the monoclonal antibody VIR-3434, specifically targets this epitope to reduce circulating HBsAg levels and potentially restore host immune responses in patients with chronic Hepatitis B (Vir Biotechnology, 2023).

Other names

a determinantMajor hydrophilic regionMHRHepatitis B virus surface antigenHBV surface proteinSmall surface proteinHBsAg a-determinant

Neutralization of viral particles by blocking attachment to host receptors and promoting immune-mediated clearance of circulating antigens.