Hepatitis B virus small surface antigen (S-HBsAg)

Hepatitis B virus small surface antigen (S-HBsAg) is a glycosylated integral membrane protein that constitutes the primary structural component of the HBV viral envelope and forms the basis of the majority of currently licensed HBV vaccines[1][3][4][5]. S-HBsAg assembles into both infectious viral particles and non-infectious subviral particles (SVPs), the latter being produced in great excess during HBV infection[1][3][4]. These particles are highly immunogenic, serve as key antigens in serological diagnosis, and act as immune decoys to facilitate viral escape from host immunity[1][3][5]. S-HBsAg dimers organize into octahedral or icosahedral arrays that form the shell of SVPs and virions[3][4]. The S-HBsAg protein is also involved in immune modulation, contributing to HBV's ability to evade both innate and adaptive immune responses; it can interfere with dendritic cell and monocyte function, impair T cell activation, and promote immune tolerance[5]. Persistence of S-HBsAg is associated with chronic infection and increased risk of hepatocellular carcinoma, making it both a diagnostic marker and therapeutic target in HBV infection[5]. Monoclonal antibodies and vaccines target this antigen to block infection and clear circulating virus[2][4].

Other names

Hepatitis B surface antigen (small form)S-HBsAgSmall HBsAgHBV S antigen

Neutralizing antibodies bind S-HBsAg to prevent viral entry and mediate immune clearance. Vaccines induce immune response (anti-HBs antibodies) that neutralize HBV infection. Antibodies may block the antigenic loop (AGL) or other epitopes, reducing infectivity.