What is hepatitis B virus?

What is hepatitis B virus?

What is hepatitis B virus?

It is a DNA virus belonging to the Hepadnavividae family and is a spherical particle with a diameter of 42 nm. Also known as Dane particles, there are two parts of the outer shell and the core. The outer shell is 7-8 nm thick, has a surface antigen (HBsAg), has a core diameter of 27 nm, and contains partially double-stranded, partially single-stranded circular DNA, DNA polymerase, core antigen and e antigen. The genome of HBV DNA contains approximately 3200 base pairs. The length of the long chain is fixed, and there is a nick here where DAN polymerase; the length of the short chain is variable. When HVB replicates, the endogenous DNA polymerase repairs the short strand, making it a complete double-stranded structure, and then transcribed. The long chain of HBV DNA has four open reading frames (ORFs), namely S region, C region, P region and X region. The S region includes the pre-S1 pre-S2 and S region genes, encoding the pre-S1, pre-S2 and S coat proteins; the C region includes the pre-C region, the C region gene encodes the HBcAg protein, and the pre-C region encodes a signal peptide, which is assembled. It plays an important role in secreting viral particles and in the secretion of HBeAg; the P gene encodes a DNA polymerase; the product of the X gene is an X protein, the function of which is unclear. The short chain of HBV DNA does not contain an open reading frame and therefore cannot encode a protein.
In the serum of patients with hepatitis B, three kinds of particles can be found under the microscope observation:

• Small spherical particles having a diameter of 22 nm;
• Tubular particles, about 100 ~ 700nm long, about 22nm wide;
• Large spherical particles having a diameter of 42 nm.

Small spherical particles. The small spherical particles and the tubular particles are all excess viral outer shells, containing surface antigens, large spherical particles, ie, viral particles, both solid and hollow, and the hollow particles lack nucleic acids.



1. Hepatitis B surface antigen (HBsAg) and surface antibodies (anti-HBs) HBsAg are present in the outer shell of the virus particles as well as small spherical particles and tubular particles. 2-12 weeks after infection, alanine aminotransferase (ALT) can be measured from the blood before it rises, usually lasts for 4 to 12 weeks, until the recovery period disappears, but the infection persists for a long time. HBsAg is non-infectious and antigenic, and can stimulate the body to produce anti-HBs. Anti-HBs can be detected from blood soon after the disappearance of HBsAg from blood, or weeks or months. The titer of anti-HBs increases gradually and persists for many years. Anti-HBs have a protective effect on isotype infections. The anti-HBs produced by recent infections belong to IgM, while the long-term presence of blood is anti-HBs IgG.

2. Hepatitis B core antigen (HBcAg) and core antibody (anti-HBc)
HBcAg is mainly present in the nucleus of infected liver cells. After replication, it is released into the cytoplasm, encapsulated by HBsAg formed in the cytoplasm, assembled into intact virus particles and released into the blood. Free HBcAg is generally not found in the blood. The Dane particles in the blood can be found in the core part of HBcAg and DNA polymerase after being treated with detergent.

HBV DNA polymerase is present in the core of Dane particles and is a DNA-dependent DNA polymerase whose function is related to the repair and extension of short strands of double-stranded DNA. Increased HBV DNA polymerase activity in the patient's serum is often accompanied by HBV proliferation. During the incubation period of acute hepatitis B, serum DNA polymerase activity is elevated before serum ALT is elevated. Therefore, DNA polymerase activity assay has early diagnostic significance. In patients with acute hepatitis, if the activity of HBV DNA polymerase continues to increase after 1 month of onset, it is a sign that hepatitis has become chronic.

3. Hepatitis B e antigen (HBeAg) and e antibody-(HBe)
HBeAg is a soluble protein in the HBV core in a concealed form, and its coding genes overlap each other and are sub-components of HBcAg. After infection with HBV, HBeAg can appear in the blood simultaneously or later with HBsAg, and it disappears slightly earlier than HBsAg. HBsAg is only present in the blood of HBsAg-positive people, usually accompanied by replication of HBV DNA in the liver, and there are more Dane particles and HBV DNA polymerase activity in the blood. Therefore, HBeAg-positive is an important indicator of active replication of the virus, and is highly contagious.