Transcript Haemophilus influenzae

Retroviruses and AIDS
Dr Amanj Saeed
MB.CH.B, MSc, PhD
[email protected]
Discovery of retroviruses
• Retroviruses possess a unique enzyme known as RT
(reverse transcriptase)
• RT uses viral RNA as a template for making DNA copy
which integrate in to the chromosome of the host cell and
serves either as basis for viral replication or as oncogene.
• Howard Temin and David Baltimore received Nobel Prize
for discovery of RT enzyme.
Discovery of HIV
• In 1981 new clinical syndrome characterized by
profound immunodeficiency was recorded in male
homosexual and termed AIDS.
• Unusual prevalence of Pneumocystis carinii
pneumonia in in a group of young previously healthy
male homosexual.
Kaposi’s sarcoma (rare cancer) in
previously healthy male
homosexual??
Discovery of HIV
First isolation of HIV-1 made by Luc Montagnier and BarreSinoussi at Pasteur institute in Paris in 1983.
This observation is confirmed by Robert Gallo in the USA.
Discovery of HIV
HIV-2 isolated from mildly immunosuppressed patient n
west Africa.
5000 cases of HIV-1 cases per Day?
41 million people have been infected world wide.
HIV-2 account for 4.5% of HIV cases.
Retroviridae
HIV-1
Le nt iv ir us
Visna
MMTV
Be t a
SRV-1
HERV-K
Alpha
RSV
HTLV-I
HTLV-II
De lt a
BLV
MLV
Ga m m a
FLV
WDSV
Ep s i l o n
FFV
Sp u m a v ir u s
SFV
Lentiviruses
Primates infected
with lentiviruses
Human
Chimpanzee
Bonobo
Gorilla
Orangutan
Gibbon
Sykes's
Vervet
Grivet
Tantalus
Sabeaus
Patas
L'Hoest's
Sun-tailed
Preussi's
Mandrill
Drill
Sooty mangabey
Agile mangabey
Macaque
Yellow baboon
Chacma baboon
Colobus
Langur
> 30 species of African
primates naturally infected
with SIV
SIV infections:
natural
acquired
not known
Natural infections:
• >50% of adults
• nonpathogenic
Chimpanzee the only ape
25
0 my
Primate Lentiviruses
HIV-2
Photograph by Karl Ammann
Photograph by Karl Ammann
Properties of HIV
Classification
The family Retroviridae is named for RT.
(Retro= Backwards)
Seven genera is now recognised (only two of them cause
disease in human):
Lentivirus: containing HIV-1 and HIV-2, characterised by:
Cone shaped Nucleocapsid, absence of oncogenicity, and
the lengthy and insidious onset of clinical signs.
Properties of HIV
BLV-HTLV retroviruses: contain HTLV-I and II:
characterised by ability to cause tumours rather than
immunosuppression.
Spumavirus : Causes characteristic foamy appearance in
infected primate cell culture. (they are not pathogenic).
Global estimates for adults and children  2010
People living with HIV
34.0 million [31.6 million – 35.2 million]
New HIV infections in 2010
2.7 million [2.4 million – 2.9 million]
Deaths due to AIDS in 2010
1.8 million [1.6 million – 1.9 million]
Adults and children estimated to be living with HIV  2010
Eastern Europe
Western &
Central Europe & Central Asia
840 000
1.5 million
[770 000 – 930 000][1.3 million – 1.7 million]
North America
1.3 million
East Asia
[1.0 million – 1.9 million]
790 000
Middle East & North Africa
Caribbean
200 000
[170 000 – 220 000]
Latin America
1.5 million
[1.2 million – 1.7 million]
[580 000 – 1.1 million]
470 000
[350 000 – 570 000]
South & South-East Asia
4.0 million
Sub-Saharan Africa
[3.6 million – 4.5 million]
[21.6 million – 24.1 million]
Oceania
22.9 million
54 000
[48 000 – 62 000]
Total: 34.0 million [31.6 million – 35.2 million]
Estimated number of adults and children
newly infected with HIV  2010
Eastern Europe
Western &
Central Europe & Central Asia
30 000
[22 000 – 39 000]
North America
58 000
160 000
[110 000 – 200 000]
[24 000 – 130 000]
Middle East & North Africa
Caribbean
12 000
[9400 – 17 000]
Latin America
100 000
[73 000 – 140 000]
East Asia
88 000
[48 000 – 160 000]
59 000
[40 000 – 73 000]
South & South-East Asia
270 000
Sub-Saharan Africa
1.9 million
[1.7 million – 2.1 million]
[230 000 – 340 000]
Oceania
3300
[2400 – 4200]
Total: 2.7 million [2.4 million – 2.9 million]
Estimated adult and child deaths from AIDS  2010
Eastern Europe
Western &
Central Europe & Central Asia
9900
[8900 – 11 000]
North America
20 000
90 000
[74 000 – 110 000]
East Asia
[16 000 – 27 000]
56 000
Middle East & North Africa
Caribbean
9000
[6900 – 12 000]
Latin America
67 000
[45 000 – 92 000]
[40 000 – 76 000]
35 000
[25 000 – 42 000]
South & South-East Asia
250 000
Sub-Saharan Africa
1.2 million
[1.1 million – 1.4 million]
[210 000 – 280 000]
Oceania
1600
[1200 – 2000]
Total: 1.8 million [1.6 million – 1.9 million]
Children (<15 years) estimated to be living with HIV  2010
Eastern Europe
Western &
Central Europe & Central Asia
1400
[<1000 – 1800]
North America
4500
17 000
[14 000 – 23 000]
East Asia
[4000 – 5800]
16 000
Middle East & North Africa
Caribbean
16 000
[12 000 – 19 000]
Latin America
42 000
[30 000 – 54 000]
[11 000 – 21 000]
40 000
[27 000 – 52 000]
South & South-East Asia
160 000
Sub-Saharan Africa
3.1 million
[2.8 million – 3.5 million]
[110 000 – 210 000]
Oceania
4600
[3600 – 5800]
Total: 3.4 million [3.0 million – 3.8 million]
Estimated number of children (<15 years)
newly infected with HIV  2010
Eastern Europe
Western &
Central Europe & Central Asia
<100
[<200]
North America
<100
2200
[1700 – 2900]
East Asia
[<200]
2100
Middle East & North Africa
Caribbean
1200
[<1000 – 1700]
Latin America
3500
[2100 – 5000]
[<1000 – 3800]
6800
[4800 – 8800]
South & South-East Asia
20 000
Sub-Saharan Africa
[14 000 – 28 000]
[300 000 – 410 000]
Oceania
350 000
<1000
[<500 – <1000]
Total: 390 000 [340 000 – 450 000]
Estimated deaths in children (<15 years) from AIDS  2010
Eastern Europe
Western &
Central Europe & Central Asia
<100
[<200]
North America
<100
1200
[<1000 – 1800]
East Asia
[<200]
1100
Middle East & North Africa
Caribbean
1000
[<1000 – 1300]
Latin America
2400
[1300 – 3500]
[<1000 – 1700]
3900
[2700 – 5000]
South & South-East Asia
14 000
Sub-Saharan Africa
[8300 – 20 000]
[200 000 – 260 000]
Oceania
230 000
<500
[<500 – <500]
Morphology of HIV
HIV particle is 100-150 nm in diameter.
Outer envelope of lipid penetrated by 72 glycoprotein spike
(the lipid envelope protein)
The envelope protein is composed of two subunits: the outer
glycoprotein knob (gp120) and transmembrane protein
(gp41)
The receptor binding site for CD4 is present on gp120 as
well as very important antigen such as V3 loop.
Morphology of HIV
The inner surface of virus lipid envelope is lined by matrix
protein (p17)?.
There is also abundant cellular proteins in the lipid envelope
(MHC class I and II) antigens.
In HIV-1 the lipid envelope encloses an icosahedral shell of
protein (p17), within which is a vase or cone shaped
protein core (p24, p7, and p9) containing two molecules
of positive sense ssRNA
The RNA genome is associated with several copies of RT,
integrase, and protease.
HIV genome
Positive sense ssRNA genome
The genome is approximately 10kb in size
The genome contain control genes which can enhance viral
replication:
rev: regulator of virus
tat: transactivation.
vif: viral infectivity
repressor genes:
nef: negative factor
HIV genome
The genome is flanked at each end by LTR
3’ LTR has the polyadenylation signal and 5’LTR has the
enhancer promotor sequence for viral transcription.
The pol gene code for RT, integrase and protease.
The HIV-1 genome
rev
vif
tat
nef
5’ LTR
vpr
gag
p17 matrix antigen
p24 capsid antigen
p6/7 nucleocapsid
pol
reverse transcriptase
protease
integrase
3’ LTR
vpu
env
envelope glycoprotein (gp120)
transmembrane
glycoprotein (gp41)
HIV genome
HIV binds to specific receptor on the surface of CD4+ T
lymphocytes (T-helper cells)
It also infects:
•
B lymphocytes
•
Macrophages
•
dendritic cells
•
brain cells.
Second subsidiary receptor belongs to chemokine receptor
family CXCR4 on the T-cells and CCR5 on the surface of
macrophages.
Retroviruses
HIV lifecycle
virus binding
maturation
fusion
virion assembly and release
ssRNA (+)
reverse transcription
dsDNA
translation of viral proteins
nuclear transport
integration
nucleus
transcription
cytoplasm
HIV life cycle
After attachment the virus penetrate the cell by fusion from
without (Mediated by gp21 and gp41)
Synthesis of viral cDNA starts when the virion enters the cell
cytoplasm.
The viral RT enzyme directs the synthesis of cDNA strand
(the minus strand) using host positive RNA as a primer
and the viral genomic RNA as a template.
Viral RNAse enzymatically remove the viral RNA while the
RT synthesize the second DNA strand (plus strand).
HIV life cycle
Viral dsDNA will enter the Nucleolus of the host cell as a
pre-integration complex (compose of viral protein M,
Vpr, integrase, and dsDNA)
the integration of dsDNA to the host chromosome occurs
(forming pro-viral DNA)
After integration viral and cellular factors are needed to
activate HIV transcription.
Initial expression of viral RNA is stimulated by vpr and
further stimulated by cellular transcription factors .
HIV life cycle
The primary RNA transcript is spliced to give 30 plus strand
viral mRNAs.
Viral and cellular factors are required for early and late viral
protein expression.
Early viral gene product include (tat, rev, and nef),
accessory viral proteins (vif, vpr, and vpu)
Late viral gene products include (gap, pol and. env).
HIV life cycle
Assembly of new virion can begin by proteolytic cascade by
viral proteases.
Different viral structural proteins begin to assemble with the
p24 as a core and p7 enclosing viral RNA.
Viral genome assemble in the cytoplasm.
Retroviruses including HIV are release from the infected
cells by budding from the infected cells.
The pro viral DNA may reside quietly in the
chromosome for years.
Genetic Variability
RT has NO proof-reading mechanism therefore mutations
(point point mutations and deletions/insertions) occur
Quasispecies = swarm of genetically distinct yet related
viruses
Effects of Variability
Immune escape by changing/masking antigenic determinants
• CTLs and Abs
Resistance to anti-retroviral drugs
• Point mutations in enzymatic proteins
- RT - resistance to nucleoside and non-nucleoside analogues
- Protease - resistance to protease inhibitors
Altered cytopathogenicity
• Env and particularly V3 mutations alter co-receptor usage
- Different cell tropism, eg. Macrophages, T-cells, glial cells,
langerhans cells etc.
- Different tissue tropisms, e.g. brain
Integration
Double stranded cDNA (provirus) migrates to nucleus
Can exist extra-chromosomally as linear or circular form
Can integrate via the enzyme integrase
Activation
Once integrated the provirus responds to cellular nuclear
factors e.g. SP1, NF-kB
Mediated through control regions in the 5’ LTR
Once active viral factors take over
Transactivation then control of RNA splicing events
Translation
Translation I.e.viral protein production
Virus release via budding on cell membrane
Morphological characteristics of budding virus is used for
classification
• type C, Type D morphology refers to morphology of budding/maturing
virus
Summary
HIV member of the Retroviridae family (reverse
transcriptase)
Entry mediated by CD4 plus co-receptor
Reverse transcription leads to errors
Virus can become integrated into chromosome (can
be latent)
Transcription – short (spliced) then long RNAs
New virus buds at surface
Three main targets for therapy