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The structure of the hepatitis B virus
Last reviewed: 06.07.2025
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The hepatitis B virus is a spherical formation with a diameter of 42-45 nm, has an outer lipoprotein membrane and an internal part - the nucleocapsid or core of the virus.
The outer shell of the virus is located in the cytoplasm of the infected hepatocyte and contains protein antigens: superficial (superficialis) HBsAg and pre-S1, pre-S2 antigens. HBsAg is often found in the blood plasma of patients with chronic hepatitis in the form of spherical particles with a diameter of 22 nm, as well as in the form of filamentous structures with a size of 16-25 nm.
According to antigenic characteristics, there are 4 main subtypes of HBsAg: adw, adr, ayw, ayr, depending on the content of one common group-specific determinant a and two of the four subtype determinants d, y, w, r.
On the outer shell of the hepatitis B virus in the zone preceding the HBsAg region, there are protein antigens pre-Sl » pre-S2. These antigens play a huge role in the mechanism of interaction of the hepatitis B virus with hepatocytes.
The internal part of the hepatitis B virus (nucleocapsid) penetrates the nucleus of the hepatocyte and contains the following components:
- HBcAg (HBcoreAg) is a core antigen, localized exclusively in the nuclei of hepatocytes and is not detected in the blood;
- HBprecoreAg (HBeAg) - is localized in the nucleocapsid of the virus next to HBcAg, representing its secreted soluble part; the existence of two variants of HBeAg is allowed - HBeAgl and HBeAg2, differing in the degree of connection with HBcAg, HBeAg circulates in the blood;
- HBxAg - information about its significance is still insufficient; it is assumed that it may be an inducer of the body's tolerance to the hepatitis B virus;
- HBpol is a marker of DNA polymerase synthesis;
- hepatitis B virus genome HBV-DNA - a circular double-stranded DNA molecule; one strand (chain) is 30% shorter than the other. The missing part of the DNA is built up from the host's nucleotides using DNA polymerase;
- DNA polymerase enzyme.
The hepatitis B virus genome (DNA) contains the following genes encoding the synthesis of antigens:
- pre-S/S gene - encodes the synthesis of HBsAg, as well as pre-Sl and pre-S2;
- gene C - encodes the synthesis of HBcAg and HBeAg;
- gene X - encodes the synthesis of HBxAg, regulates the expression of viral genes and the process of HBV replication;
- The P gene is a polymerase gene that mainly encodes the HBpol marker and also participates in the encoding of HBcAg.
In the body of a patient with viral hepatitis B, antibodies are produced to all viral antigens (HBcAg, HBeAg, HBsAg, pre-Sl, pre-S2, HBxAg, Hbpol): anti-HBc, anti-HBe, anti-HBs, anti-pre-Sl, anti-HTH-pre-S2, anti-HBx, anti-HBpol. These antigens and antibodies to them represent a complex of specific HBV markers. Determination of these markers has diagnostic, prognostic and epidemiological significance. The significance of determining anti-HBx and anti-HBpol in the blood is still not well known.