HBV

Rough working notes, 6/2006, users.monash.edu/~lloyd/tildeStrings/Virus/HBV/index.shtml

The Cast

1. Virus: Its parts in the various stages of its ["life"-cycle].
2. Liver: Hepatocytes, ~ 10¹² cells [Lit05].
3. [Immune system]:
   1. T_H cells (helper T-cells).
   2. CTL cells (cytotoxic, killer T-cells).
   3. B-cells, antibodies.
4. Drug(s), ?3TC?, lamiduvine, adefovir, entecavir.

Genome: Incomplete double-stranded DNA

Long, medium and short versions (LHB, MHB, SHB) of surface protein, S, depending on start site.

Long "involved" in entering cell.

Polymerase, P, includes the reverse-transcriptase, RT.

Pol is bound to the pre-genomic RNA which it processes to DNA after packaging, then bound to the DNA until after DNA entry into cell nucleus.

Major dual reading frame overlap, S:P, means that mutations in one gene may affect the other protein.

Long Pre_C+C, and short real C. Latter makes the core (shell) of viral particle.

Pre-core accessory protein. Thought to suppress immune system response, e.g., [Wie05].

Also see [HHL00]; HBeAg -ve (pre-core -ve) => many mutations v. +ve.

NB. Core produced from pre-genomic RNA, pre-core from a separate, long(!), mRNA.

X, "accessory protein" [LL04, p.313],

multipurpose regulator, ?implicated cancer?, dampen immune sys., e.g., [Wie05].

HBV virion ~ 42nm dia..

Also see "dud" 22nm viron± particles, and misc. HBsAG^* particles in serum.

Polymerase, RT

"Life"-cycle

1. Viron in serum.
2. Attach; get through membrane.
3. Uncoating from the surface proteins.
4. Genome & attached Pol. enter nucleus;
5. Remove Pol.. Repair to ccc-DNA, covalently closed circular DNA (by cell). Form mini chromosomes.
6. Ccc DNA transcribed to mRNA; exported from nucleus.

7. Pre-S1 RNA -> long surface.

   Pre-S2 RNA -> medium and short surface.

   Pre-genomic RNA -> core and Pol..

   Pre-core RNA -> pre-core protein.

   X RNA -> X.

8. Packaging of pre-genomic RNA and Pol. in core icosahedron.
9. Pregenomic RNA (3.5K) reverse transcribed (RT) to DNA inside viral capsule.

   (i)  RNA, 3' to 5', -> DNA -ve strand (and RNA degraded).

   (ii) DNA -ve, 3' to 5' -> DNA +ve synthesised.

   The (incomplete) strands are attached to Pol..

   ? RT seems to get just one chance per viron at doing its job? ?3K (?6K) choices to make. Good target.

   ? How active, how specific, is RT during RNA -> DNA?

   "mutn rate 1.4 to 3.2×10^-5 mut./site/y", [Loc04 p.6], "10× most DNA viruses" (still seems quite specific -LA).

   NB. Some capsules re-cycled into nucleus to boost ccc-DNA. (At what stage?)

10. Envelopment of core by surface proteins after rev. transcription starts;
11. Exit cell.

HBV infection

Hepatocyte ~ a kind of liver cell. ?What other kinds?

Acute infection

and viral clearance.

Chronic infection

T_H2 cells -> antibody prodn but no viral clearance. Weak CTL response, persistent inflammation, may lead to cancer. [LL04]

?Does not remove source of production?

Immune System

Adaptive Immunity (T_H, CTL, antibodies, B-cell).

Antigen Presenting Cells (APCs): A misc. collection of cells inc. dendritic, B-cells and macrophages [Alb94, p.1240]; present antigens to T_H cells.

(i)  ? APC --[contact antigen & (IL1 or B7)]-> ? T_H1 --[IL2 γ-interf.]-> CTL cells [LL04 p.302] [Alb94 p.1245],
CTLs recognise antigen displayed by infected hepatocytes, kill them, removing source of production.

(ii) APC --[contact antigen & (IL1 or B7)]-> T_H2 --[contact match & IL4, IL5]-> B-cell which v.specifically make antibodies which bind to free particles -> "complement" proteins mop them up.

(If only 1 signal, T_H inactivated, ?tolerance? [Alb94 p.1242].)

Innate Immunity?

natural killer cells (NK, NKT) attack infected hepatocytes.

An antibody is specific to an antigen; made by a B-cell clonal family, binds to matched free antigen; neutralizes antigen.

Human makes >10¹⁵ different antib. molecules [Alb94 p.1221]. ?quantity or variety?

An infected cell, displaying an antigen (12-15 AAs) on its surface, may be targetted for attack by CTLs.

APCs (good) present antigens to T_H cells which signal CTLs and B-cells.

Sources

[Alb94] B. Alberts et al. The Molecular Biology of the Cell. Garland, 3rd edn 1994.

Ch.23 p.1195-1254, the immune system.

[BTC04] A. Bartholomeusz, B. G. Tehan, D. K. Chalmers. Comparisons of the HBV and HIV polymerase, and antiviral resistance mutations. Antiviral Therapy, 9, pp.149-160, 2004.

3TC -> rtM204I/V, rtL180M, p.150; (rtL80I/V or rtL82M) & rtM204I, p.153; adefovir -> rtN236T, ±rtA181V/T

[HHL00] C. Hannoun, P. Horal, M. Lindh. Long-term mutation rates in the hepatitis B virus genome. J. General Virology, 81, pp.75-83, 2000.

3 mothers, total 10 adult children, avg 26.5y	HBeAg +ve (pre-core)	chronic	9mutn(×1)
		mild	0-2mutn, v.stable
	HBeAg - ve	severe	19,27mutn
		mild	15,19,20mutn

and 10⁸/ml "high", 10^5.5/ml "moderate". p.77 p.78 re pre-core (HBeAg) `stop' mutations.

p.76 & p.77, v. NCBI genomes, B: D00329 - D00331, D23678, D23679, D50521, D50522, M54923, X97851, X9807. D: J02203, L27106, M32138, U95551, X02496, Z35716, X68292, X85254, X80925.

[LL04] J. Y. Lee, S. Locarnini. Hepatitis B virus: pathogenesis, viral intermediates, and viral replication. Clin. Liver Dis., 8, pp.301-320, 2004.

lamiduvine -> rtM205I/V, rtL180M; famciclovir -> rtL180M; adefovir -> rtN236T; --p.313.

[Lit05] S. Litwin, E. Toll, A. R. Jilbert, W. S. Mason. The competing roles of virus replication and hepatocyte death rates in the emergence of drug resistant mutants: Theoretical considerations. J.Clinical Virol., 34(S1), s96-s107, 2005.

... 10¹² hepatocytes... human liver.   mutn rate ~ 10^-4 mut./site/year.

[Loc04] S. Locarnini. Molecular Virology of Hepatitis B Virus. Seminars in Liver Dis., 24 (S1), pp.3-10, 2004.

mutn rate 1.4 to 3.2×10^-5 mut./site/y., load can be ~ 10¹¹virions/ml, half-life in serum ~ 1-2 d, production ~ 10¹¹v/d,

[Wie05] S. F. Wieland & F. V. Chisari. Stealth and Cunning: Hepatitis B and Hepatitis C Viruses. J.Virology, 79(15), pp.9369-9380, Aug. 2005

HBeAg has been shown to suppress the antibody & T-cell response... (HBsAg) might also suppress immune elimination of infected cells... HBx protein has the potential to inhibit antigen processing... as many as 10**11 hepatocytes can be infected

Wikipedia [2006], [Liver], [Hepatocyte], [Hepatitis], [HBV], [immune-system],

Liver 1.3-3.0kg, "Hepatocytes make up 60-80% of the cytoplasmic mass of the liver", ">95% of people who become infected as adults or older children will stage a full recovery", "[HBV] one of a few known non-retroviral viruses which employ reverse transcription".

Also see [Bibliography].