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Rough working notes, 6/2006,
users.monash.edu.au/~lloyd/tildeStrings/Virus/HBV/index.shtml
The Cast
- Virus:
Its parts in the various stages of its
["life"-cycle].
- Liver:
Hepatocytes, ~ 1012 cells [Lit05].
- [Immune system]:
- TH cells (helper T-cells).
- CTL cells (cytotoxic, killer T-cells).
- B-cells, antibodies.
- Drug(s), ?3TC?, lamiduvine, adefovir, entecavir.
Genome: Incomplete double-stranded DNA
m R N A |
NB. scale is only very approximate! |
3.2K ± |
| | | | | | | .8 |
| | | | | | | 1.6 |
| | | | | | | 2.4 |
| | | | | | | 3.2 |
|
... |
|
+strand DNA... |
|
... |
|
- strand DNA... |
|
...Pre-S2
|
>S> |
|
>Pre-S1
|
>... |
LHB 2.4k |
... |
|
*gp42 (env) ... |
MHB & SHB 2.1k |
... |
*HBsAg (gp27, env) |
|
*gp36 (env) ... |
|
...> |
|
>P... |
pre- gen 3.5k pol & core
|
... |
*DNA-pol ... |
... |
|
RNaseH |
term. prot. |
spacer ... |
|
*HBcAg (core) |
|
|
|
>Pre-C
|
>C> |
|
pre- core 3.5k+ |
|
*HBeAg |
|
|
|
>X> |
|
X 0.7k |
|
HBxAg |
|
|
.1 | | | | | | | .8 |
| | | | | | | 1.6 |
| | | | | | | 2.4 |
| | | | | | | 3.2 |
key: |
* = initiation of transcription(?);
env = envelope;
Ag = antigen
|
- 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
<1 |
(...pre-S2...) <183 (166)
|
<349 |
(344, units=AAs) |
692> |
| (153) 845> |
terminal protein TP
| spacer
|
I(G) |
- |
II(F) |
- |
A L80V/I |
- |
B V173L
L180Ml
A181Ta
S184Ge
|
- |
C
M204V/I/Sl
S202Ie
|
- |
D
N236Ta
M250Ve
|
- |
E |
l lamiduvine,
resist. 70% after 4y.;
a adefovir,
resist. 2% after 2y.;
e entecavir (new);
-- [Loc04] p.8.
|
| RNaseH
|
after [Loc04] p.7, after Angus et al.
|
- Viron in serum.
- Attach; get through membrane.
- Uncoating from the surface proteins.
- Genome & attached Pol. enter nucleus;
- Remove Pol..
Repair to ccc-DNA, covalently closed circular DNA (by cell).
Form mini chromosomes.
- Ccc DNA transcribed to mRNA; exported from nucleus.
-
- 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.
- Packaging of pre-genomic RNA and Pol. in core icosahedron.
- 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?)
- Envelopment of core by surface proteins
after rev. transcription starts;
- Exit cell.
- Hepatocyte ~ a kind of liver cell. ?What other kinds?
- Acute infection
- and viral clearance.
- Chronic infection
- TH2 cells -> antibody prodn but no viral clearance.
Weak CTL response, persistent inflammation, may lead to cancer. [LL04]
- ?Does not remove source of production?
- Adaptive Immunity (TH, 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 TH cells.
- (i)
? APC --[contact antigen & (IL1 or B7)]-> ?
TH1 --[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)]->
TH2 --[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, TH inactivated, ?tolerance? [Alb94 p.1242].)
- Innate Immunity?
- natural killer cells (NK, NKT) attack infected hepatocytes.
Lymphocytes,
2×1012 in human body[Alb94 p.1196]
|
B-cells
Have receptors for free antigens.
Activated by TH cells, make antibodies
(soluble form of B-cell receptors).
5×107/day in mouse [Alb94 p.1198].
|
T-cells
|
Cytotoxic (killer) T-cells (CTL)
Kill infected cells on recognition of antigen on cell's surface.
|
Helper T-cells TH
Receptors bind to antigens on (good) APCs.
Activates B-cells, CTLs and more TH chemically.
AKA CD4+cells or T4-cells.
|
- 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
TH 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", 105.5/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].
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