Hepatitis-B-Virus

The hepatitis B virus ( HBV) is an enveloped double-stranded DNA virus with the genome and most of the cause of the hepatitis B. Hepatitis B virus comes from the genus within the family of the Hepadnaviridae Orthohepadnaviren.

Disease

In addition to hepatitis B HBV causes chronic cases, liver cirrhosis and liver cancer. Possibly a connection in pancreatic cancer exists. The hepatitis B virus does not produce a cytopathic effect, so the damage to the liver cells are increasingly blamed on the immune response (indirect pathogenesis, immunopathogenesis ). Due to the continuous growth stimulation to replace the destroyed by the immune system infected hepatocytes and by the cytokines with partially growth-promoting properties and by the partial insertion into the cellular DNA rise increasingly copying errors in the DNA during mitosis ( in S phase ), which is the origin favored by tumors.

Construction

The virion has a viral envelope and an icosahedral capsid. The capsid enclosing the viral DNA and a DNA polymerase having a reverse transcriptase activity (RT), similar to a retroviral polymerase. The viral envelope contains a membrane protein of the HBsAg and the Pre-S1 protein to bind to the host cell. With a diameter of 42 nm spherical HBV is more closely associated (also called Dane particle ) to the smaller animal viruses. There are also non-infectious filamentous and spherical shapes without capsid of 20 nm in diameter, since HBsAg is formed in excess. These virus -like particles comprised of HBsAg in a lipid bilayer. Due to the immunogenicity without infectivity were used in the first - hepatitis B vaccines. The HBcAg can in recombinant expression form (without HBsAg) also virus-like particles.

HBV in the blood reaches a virus concentration of 104 to 109 virions per milliliter, the virus-like particles of HBsAg particle concentration can even reach up to 1,012 particles per milliliter.

Genome

The genome of HBV is made of circular - closed DNA, but the DNA is not completely double and one strand throughout. One end of the continuous strand of about 3020-3320 nucleotides binds the viral DNA polymerase, while the shorter strand of nucleotides 1700 to 2800 is significantly shorter.

The continuous ( - ) strand ( non- coding ) is reverse - complementary to the viral mRNA. The viral DNA is already detected shortly after infection in the nucleus. The partially double-stranded DNA is completed at the ( ) strand and an RNA sequence located at the ( ) strand. Last overhanging nucleotides are removed and the ( - ) strand closed to the ring.

The four HBV genes are called C ( core) X, P (polymerase ) and S (surface ) respectively. The core protein HBcAg is generated from a pre-protein by proteolysis. The gene S protein of HBsAg contains three frameshift correct start codon ( AUG), which three proteins occur, pre-S1 (synonym L), pre-S2 (synonym M) and S.

Various non-coding RNA were identified in the genome of HBV. These are referred to as hepatitis B virus PRE alpha, beta, and hepatitis B virus PRE HBV RNA encapsidation signal epsilon respectively.

Proteins

The virion of HBV consists of four structural proteins, still coming in HBeAg outside of the virion before.

HBsAg

HBsAg ( HBV surface antigen English, HBV surface antigen ') is a surface protein of the virion, which is detected in the course of the immune response of antibodies, as an antigen. It is by virological diagnostics detected in the blood of infected people and indicates the date when the patient is no longer contagious. In histology HBsAg is detected by a Shikata - Orceinfärbung.

Historically HBsAg was first known as Australia antigen, since it was first discovered by Baruch Samuel Blumberg in the blood serum of Australian Aborigines. Alfred Prince discovered in 1968 related to a hepatitis form. The first vaccine against HBV ( Heptavax ) was purified from the blood plasma of HBV -infected patients, due to the risk of contamination by other pathogens was later converted to recombinant proteins from baker's yeast.

Hepatitis D virus requires HBsAg to be pathogenic.

HBcAg

HBcAg (English core antigen of the virus core antigen ' ) is used for packaging of the viral DNA and is used for detecting a current infection.

HBeAg

HBeAg (English extracellular antigen, extracellular antigen ') is a splice variant of the open reading frames ORF - core and pre -C ORF. HBeAg is secreted and does not occur in the virion. HBeAg as HBcAg is used to detect a current infection. Presumably, it is used to minimize the gene expression of Toll-like receptor 2 on hepatocytes and monocytes, and thus an attenuation of the immune response against HBV. HBeAg is not essential, ie virions without HBeAg expression are infectious and pathogenic.

Hepatitis B virus DNA polymerase

The DNA polymerase of the HBV is the replication of the viral genome. Lamivudine and penciclovir inhibit of non-resistant HBV strains the polymerase.

HBx

Using the function of the X protein is poorly understood. Possibly comes from the X protein of a DNA glycosylase. HBx increases the release of calcium ions from the mitochondria. The HBx alters the cellular transcription, the cell cycle and forms a protein complex with the cellular protein HBX interacting protein ( HBXIP ), which interacts with the spindle apparatus during cell division. Furthermore, HBx interacts with Damaged DNA Binding Protein 1 ( DDB1 ) and inhibits the CUL4 - DDB1 E3 complexes and thereby the ubiquitin -proteasome system. HBx promotes cell division and thereby promotes the formation of tumors. HBx inhibits the protein -arginine methyltransferase PRMT1, which increases the replication of the HBV.

Occurrence and genotypes

The eight genotypes of HBV are named A through H. Possibly a genotype I, which is not accepted unanimously exists. The different genotypes respond differently to therapies.

The genotypes differ by at least eight per cent on the genomic level and have different geographical frequencies. The genotype F differs from the other most, with fourteen percent difference. The genotype A is prevalent in Europe, Africa and South Asia, including the Philippines. Genotypes B and C are prevalent in Asia; the genotype D occurs in the Mediterranean, the Middle East and India. The genotype E exists in sub-Saharan Africa. The genotype F ( or H) is found in Central and South America. The genotype G was found in France and Germany. The genotypes A, D and F dominate in Brazil and all genotypes occur with ethnic clusters in the United States.

Within the genotypes 24 subtypes have been described which differ in their DNA sequence to one another by four to eight percent.

• Genotype B has two geographically separate subtypes: Bj/B1 ( ' j' - Japan) and Ba/B2 ('a' - Asia). Ba genotype is further subdivided into four clades (B2 - B4).

• Genotype C also has two geographically separate subtypes: Cs ( C1) in Southeast Asia and Ce ( C2) in East Asia. The C subtype is divided into five clades, while a possible sixth (C6) and seventh (C7) have been found only in one isolate in the Philippines and West Papua. The genotype C1 occurs in Vietnam, Myanmar and Thailand. The genotype C2 occurs in Japan, Korea and China. The genotype C3 is found in New Caledonia and Polynesia. The genotype C4 comes in Australia, and C5 in the Philippines.

• Genotype D is divided into seven subtypes ( D1 - D7).

• Genotype E has only one subtype.

• Genotype F is divided into four subtypes ( F1 - F4). Subtype F1 is further separated into clades 1a and 1b. In Venezuela, the subtypes F1, F2 and F3 are found in the west and the east, while F3 occurs solely in the south. The subtype Ia occurs in Central America, the subtype III in northern South America and southern South America IV. The clade Ib is on almost the whole American continent (except the northern South America ) and the clade II is found in Central and South America.

Evolution

The accurate determination of the early development of the HBV is problematic. The splitting in the hepadnaviruses in ortho-and Avihepadnaviren took place about 125,000 years ago (95 % interval from 78.297 to 313.500 ). Both Avi and Orthohepadnaviren began about 25,000 years ago to become more change. At that time was the split into the eight genotypes. Humane Hepadnaviruses parted before about 7,000 (95 % interval: 5.287 to 9.270 ) to 10,000 years (95 % interval: 6.305 to 16.681 ). The Avihepadnaviren lack the X protein, but are still remnants found in Entenhepadnavirus. The rate of non- synonymous mutations in the HBV was estimated to be about 2 x 10-5 amino acid substitutions per site per year. The average frequency of nucleotide substitutions per site per year was estimated to be about 7.9 x 10-5. Another estimate suggested the last common ancestor of human HBV strains 1,500 years ago, and separation of the Avihepadnaviren 6,000 years ago at a mutation rate of about 10-6 substitutions per site per year.

Classification

HBV is a typical representative of the Orthohepadnaviren which has three additional representatives: the ground squirrel hepatitis virus, the woodchuck hepatitis virus, and the Woolly monkey hepatitis B virus. The Hepadnaviridae family contains two other genera, the Avihepadnaviren and an even Calling. The family has not yet been assigned order. HBV -like viruses have been found in all Old World monkey ( orangutan, gibbons, gorillas and chimpanzees) and also detected in New World monkeys such as the woolly monkey, suggesting an ancient origin of this virus in primates.

HBV are four serotypes (adr, adw, ayr, ayw ) divided, depending on the antigenic epitopes on their coat proteins, genetically they are, depending on their mutations, eight genotypes ( AH) associated. The individual genotypes have different geographical distribution and used to determine the epidemiological transmission and viral evolution. The different genotypes also exhibit differences in the progression of the disease, the incidence of complications as well as in therapy and vaccine choice.

Replication cycle

The replication cycle of HBV:

• Low -affinity attachment (English adsorption ) to the cell membrane via glycosaminoglycans, then binding to NTCP (Na - taurocholate cotransporting polypeptide ) and subsequent endocytosis via a yet unknown mechanism.
• Penetration (English penetration or uncoating ) by induced fusion of the viral envelope and the endosomal membrane, whereby the core is released to the DNA of the virus into the cytosol.
• Unzip (English uncoating ) and transport into the nucleus via chaperones. This results in the release of the DNA from the core, and then completing the (-) strand and the ring closure to the cccDNA which as a template for transcription of four viral mRNA (pre- S 1 / L, the pre- S2 / M, S and X) and the two RNA used for the expression and synthesis of genome (C / P and Pre -C ) is used. All viral RNA wear a cap structure and a poly -A tail.
• Replication (English replication ) in the cytosol, in the longest RNA ( C / P is longer than the viral DNA genome ) is used as a template for synthesis of the viral DNA genome, as well as the protein of the capsid, and the viral polymerase. RNA intermediate increases the mutation rate for generating escape mutations. The cccDNA is up to the time of the synthesis of HBcAg and HBsAg envelope proteins imported ( by replication ) into the nucleus, only by the coat proteins is effected an export from the nucleus of the cccDNA. Due to the nuclear import of the genome caused by the provision of unpackaged viral genomes in the nucleus which occurs occasionally persistent infection.
• Assembling (English assembly) of the new virions to a constriction of the cell, or a return of the following to the nucleus where the DNA is separated from the HBcAg and a new genome synthesis begins.
• Release ( Release Sheet ) of Tochtervirionen while synthesis of the DNA genome in the cytoplasm of the longest mRNA by RT activity of the viral polymerase.

Environmental stability

As an enveloped virus the hepatitis B virus is sensitive to chemical or physical disinfection methods, but is inactivated relatively slowly due to the high protein content in the viral envelope compared to other enveloped viruses by alcohols or surfactants. The inactivation of HBV by disinfection processes can be determined using the MAD test.