HBsAg is the surface antigen

Antigen

An antigen is a foreign molecule that, when introduced into the body, triggers the production of an antibody by the immune system. The immune system will then kill or neutralize the antigen that is recognized as a foreign and potentially harmful invader. These invaders can be molecules such as...

 of the Hepatitis

Hepatitis

Hepatitis is a medical condition defined by the inflammation of the liver and characterized by the presence of inflammatory cells in the tissue of the organ. The name is from the Greek hepar , the root being hepat- , meaning liver, and suffix -itis, meaning "inflammation"...

-B-Virus (HBV). It indicates current Hepatitis B infection.

Structure and function

The capsid

Capsid

A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...

 of a virus has different surface proteins from the rest of the virus which act as antigens. These antigens are recognized by antibody proteins that bind specifically to one of these surface proteins.

Immunoassay

Today, these antigen-proteins can be a genetically manufactured (e.g. transgene E. coli

Escherichia coli

Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...

) to produce material for a simple antigen test, which detects the presence of HBV

Hepatitis B virus

Hepatitis B is an infectious illness caused by hepatitis B virus which infects the liver of hominoidea, including humans, and causes an inflammation called hepatitis. Originally known as "serum hepatitis", the disease has caused epidemics in parts of Asia and Africa, and it is endemic in China...

.

It is present in the sera of patients with viral hepatitis B (with or without clinical symptoms). Patients who developed antibodies against HBsAg (anti-HBsAg seroconversion) are usually considered non-infectious.

HBsAg detection by immunoassay is used in blood screening, to establish a diagnosis of hepatitis B infection in the clinical setting (in combination with other disease markers) and to monitor antiviral treatment.

History

It is commonly referred to as the Australia Antigen. This is because it was first isolated by the American research physician and Nobel Prize

Nobel Prize

The Nobel Prizes are annual international awards bestowed by Scandinavian committees in recognition of cultural and scientific advances. The will of the Swedish chemist Alfred Nobel, the inventor of dynamite, established the prizes in 1895...

 winner Baruch S. Blumberg in the serum of an Australian Aboriginal person

Indigenous Australians

Indigenous Australians are the original inhabitants of the Australian continent and nearby islands. The Aboriginal Indigenous Australians migrated from the Indian continent around 75,000 to 100,000 years ago....

. It was discovered to be part of the virus that caused serum hepatitis by virologist Alfred Prince in 1968.

Heptavax, a "first-generation" hepatitis B vaccine

Hepatitis B vaccine

Hepatitis B vaccine is a vaccine developed for the prevention of hepatitis B virus infection. The vaccine contains one of the viral envelope proteins, hepatitis B surface antigen . It is produced by yeast cells, into which the genetic code for HBsAg has been inserted...

 in the 1980s, was made from HBsAg extracted from the blood plasma

Blood plasma

Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...

 of hepatitis patients. Current vaccines are made from recombinant

Recombinant DNA

Recombinant DNA molecules are DNA sequences that result from the use of laboratory methods to bring together genetic material from multiple sources, creating sequences that would not otherwise be found in biological organisms...

 HBsAg grown in yeast

Yeast

Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...

.