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The Virus and its Components 

[CLICK ON THUMBNAIL FOR LARGER PICTURE]
(Labelled drawings of HBV byY.H.Kao) 

Contents:
1.  Fast Facts (Click Here)
2. The Antigens (Click Here)
3. The HBV Particles (Click Here)
4. Interpretation of Hepatitis B Markers (Click Here) 

1. Fast Facts:

• Hepatitis B is caused by infection with the hepatitis B virus (HBV).
• What is a virus?
• HBV is a rather complex particle.
• It exists in three forms:
  1. The Dane Particle
  2. A spherical particle
  3. A tubular particle
• However, only the Dane Particle can infect, and it is the real virion of HBV.

2. The Antigens:

• Antigens: A contraction of "antibody generating". It refers to any molecule which can be specifically recognized by the adaptive elements of the immune system, the B cells and the T cells.
• Antigens are usually found on the surface of cells (e.g. erythrocytes have surface antigens and this classifies them according to types A,B, or O as well as the Rhesus factor.)
• Antigens are made up of proteins of the major histoincompatibility complex proteins, which may be of Class 1 or Class 2 types.

Subcontents:
1.  Hepatitis B surface antigen, HBsAg (Click Here)
2. Hepatitis B core antigen, HBcAg (Click Here)
3. Hepatitis B 'e' antigen, HBeAg (Click Here)

1. Hepatitis B surface antigen (HBsAg):

• It is the surface antigen of the inner core of the Dane particle.
• It is the earliest indicator of an acute HBV infection.
• It may also be an indicator of chronic infection.
• It is clinically useful in diagnosis of acute and chronic HBV infection, as well as for screening blood donors, hospital staff, pregnant women and dialysis patients.
• These antigens can encapsulate a core particle to form a complete infectious HBV particle.
• HBsAg actually consists of three types: 1. Small HBsAg (SHBsAg)
•                                                                 2. Middle HBsAg (MHBsAg)
•                                                                 3. Large HBsAg (LHBsAg)
• SHBsAg is the prime constituent of all hepatitis B particles.
• SHBsAg is manufactured by the virus in large quantities, and is present in the largest amount among all hepatitis B antigens.
• LHBsAg is the largest of HBV surface proteins, and may be involved in the attachment of HBV to the liver.

2. Hepatitis B core antigen (HBcAg):

• HBcAg is found on the inner core of the Dane particle.
• It has no clinical importance and is not used as a hepatitis marker.
• This is because it is not detectable in the bloodstream, but it can be detected in samples of liver cells.
• HBcAg forms encapsulates HBV DNA and DNA polymerase.
• It is synthesized in the cytoplasm and can assemble together to form core particles containing the viral genome.

3. Hepatitis B 'e' antigen (HBeAg):

• This is often present in patients with acute HBV infection.
• It indicated that HBV is currently rapidly reproducing in the patient.
• Its presence in the patient's blood means that the patient is infectious, and infectiousness depends on the amount of HBeAg in the patients blood.
• Continuing presence of antibodies to HBeAg indicated chronic liver disease.
• Antibodies to HBeAg may also be found in patients with chronic active HBV infection.

3. The HBV Particles:

Subcontents:
1. The Dane Particle (Click Here)
2. The Spherical and Tubular Particles (Click Here)

1. The Dane Particle:

• The Dane particle is 42nm in diameter.
• It is consists of two capsules, the inner one made up of HBcAg and HBeAg, the outer capsule made up of HBsAg. (?)
• The Dane particle is infectious because the inner capsule contains circular double-stranded DNA,
• and a large single standed region,
• and also a virion-associated DNA-dependent DNA polymerase.
• HBV DNA is one of the first things that can be detected after infection.

2. The Spherical and Tubular Particles:

• The spherical particle (a.k.a hepatitis B sphere) is 22nm in diameter.
• The tubular particle (a.k.a. hepatitis B filament) is also 22nm in diameter, but of varying length.
• Both does not contain any genetic information, hence they are not infectious.
• Both particles are made up solely of HBsAg.
• The spherical particle comprises mainly of small and medium HBsAg.
• The tubular particle is also made up of large HBsAg.
• These particles can be found in large quantities in a HBV carrier's blood.

4. Interpretation of Hepatitis B Markers:
 

References:
El-Fadil E Omer, 1995, Clinical significance of markers of hepatitis B
Robert's HBV Page
Hepatitis B virus (HBV) Overview
Ivan Roitt, Jonathan Brostoff, David Male, 1993, Immunology, 3rd Edition
Neil A. Campbell, 1993, Biology, 3rd Edition 

For more Information :
Dr Sing Kong Yuen

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