HBeAg is a

hepatitis B Hepatitis B is an infectious disease caused by the '' hepatitis B virus'' (HBV) that affects the liver; it is a type of viral hepatitis. It can cause both acute and chronic infection. Many people have no symptoms during an initial infection. ...

viral protein The term viral protein refers to both the products of the genome of a virus and any host proteins incorporated into the viral particle. Viral proteins are grouped according to their functions, and groups of viral proteins include structural protei ...

, produced by the

HBcAg HBcAg (core antigen) is a hepatitis B viral protein. It is an indicator of active viral replication; this means the person infected with Hepatitis B can likely transmit the virus on to another person (i.e. the person is infectious). Structure ...

reading frame. It is an indicator of active

viral replication Viral replication is the formation of biological viruses during the infection process in the target host cells. Viruses must first get into the cell before viral replication can occur. Through the generation of abundant copies of its genome ...

; this means the person infected with Hepatitis B can likely transmit the virus on to another person (i.e. the person is infectious). HBeAg is considered a marker for

cccDNA cccDNA (covalently closed circular DNA) is a special DNA structure that arises during the propagation of some viruses in the cell nucleus and may remain permanently there. It is a double-stranded DNA that originates in a linear form that is ligat ...

replication.

Structure

HBeAg is an antigen that can be found between the

icosahedral In geometry, an icosahedron ( or ) is a polyhedron with 20 faces. The name comes . The plural can be either "icosahedra" () or "icosahedrons". There are infinitely many non- similar shapes of icosahedra, some of them being more symmetrical tha ...

nucleocapsid A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or ma ...

core and the lipid

envelope An envelope is a common packaging item, usually made of thin, flat material. It is designed to contain a flat object, such as a letter (message), letter or Greeting card, card. Traditional envelopes are made from sheets of paper cut to one o ...

(the outer most layer of the

hepatitis b virus Hepatitis B virus (HBV) is a partially double-stranded DNA virus, a species of the genus '' Orthohepadnavirus'' and a member of the '' Hepadnaviridae'' family of viruses. This virus causes the disease hepatitis B. Classification Hepatitis B ...

). However, HBeAg is considered "nonparticulate" or "secretory". While both HBeAg and

are made from the same

reading frame In molecular biology, a reading frame is a specific choice out of the possible ways to read the nucleic acid sequence, sequence of nucleotides in a nucleic acid (DNA or RNA) molecule as a sequence of triplets. Where these triplets equate to amino ...

(multiple protein products can be produced from the same

DNA sequence A nucleic acid sequence is a succession of bases within the nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. This succession is denoted by a series of a set of five different letters that indicate the order of the nu ...

and when the genes "ORF Core" and "Pre C" are translated together, the result is HBeAg), HBeAg is secreted and accumulates in serum as an

immunological Immunology is a branch of biology and medicine that covers the study of immune systems in all organisms. Immunology charts, measures, and contextualizes the physiological functioning of the immune system in states of both health and disease ...

ly distinct soluble

antigen In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response. ...

. Hence the reason why the presence of both proteins together acts as a marker of viral replication, and why

antibodies An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that caus ...

to these antigens are a marker of declining replication. The presence of HBeAg in the serum of patients can serve as a marker of active replication in chronic hepatitis.

Function

Although the function of HBeAg was not clearly understood, one study demonstrated that it downregulated

Toll-like receptor Toll-like receptors (TLRs) are a class of proteins that play a key role in the innate immune system. They are single-pass membrane protein, single-spanning receptor (biochemistry), receptors usually expressed on sentinel cells such as macrophages ...

2 expression on hepatocytes and monocytes leading to a decrease in cytokine expression. HBeAg is dispensable for replication, as mutant viruses with defects in the pre-C region are both infectious and pathogenic.Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 7th ed. page 2062

References

{{Viral proteins Viral structural proteins Hepatitis B virus

Structure

Function

See also

References