4.38 Flashcards
Retroviruses characteristics (5)
• Positive strand RNA viruses (5000-12000 bp)
• Enveloped
• Contain reverse transcriptase enzyme
• Cause chronic disease long after infection
• HIV (human immunodeficiency virus) is a retrovirus
that causes AIDS (acquired immunodeficiency
syndrome)
• Contain reverse transcriptase enzyme
- Copies RNA into DNA
Cause chronic disease long after infection
- Due to integration of viral DNA into host
chromosome
HIV adsorption and penetration
M tropic (initial infection):
Receptor/coreceptor:
cells of macrophage lineage
CD4 and CCR5
HIV adsorption and penetration
T tropic (later during infection):
Receptor/coreceptor:
T cells
CD4 and CXCR4
Viral ENV protein gp120
binds to
cellular receptor
CD4 and to coreceptor
CXCR4 or CCR5
Coreceptor interaction
essential for
gp41 contact
and viral fusion with host
cell
Small number of resistant people
- lack the –
-coreceptors
HIV penetration (due to membrane fusion promoted by —)
gp41
HIV genome replication
Part 1: synthesis of viral DNA copy (2)
Reverse transcriptase (RT) synthesizes one strand of DNA using viral RNA as
the template.
Reverse transcriptase (RT) synthesizes the other strand of DNA using the newly
created viral single DNA strand above as the template.
RT enzyme is the major target for — drugs
anti-HIV
RT enzyme is — prone
error
(1 error every 10000 nts!)
~1 error per genome
Part 1: synthesis of viral DNA copy
Cellular — used as
a primer by reverse
transcriptase
tRNA
Part 1: synthesis of viral DNA copy
Several steps are required to
create a double stranded
DNA copy of the
positivesense, single-stranded RNA
genome
HIV genome replication
part 2: integration of viral DNA copy into host cell genome
Promoted by viral — enzyme
integrase
HIV genome replication
part 3: transcription of integrated viral DNA copy
to create more viral RNA
Viral DNA is transcribed into RNA by host cell RNA polymerase II
HIV protein expression
and viral assembly (2)
Viral RNA serves as mRNA for translation AND Viral RNA serves as the viral genome that is packaged into virions
Viral assembly occurs at
plasma membrane.
Virions acquire their membrane by budding of
— from the plasma membrane
nucleocapsids
Translation creates viral
—
polyproteins
Viral polyproteins get
cleaved to final mature
sizes by viral —
protease
HIV accessory factors (2)
nef
vpu
nef
decreases expression of MHC class I molecules on the surface of an infected cell, preventing killing by cytotoxic T cells
vpu
reduces cell surface CD4 expression and enhances viral release
Long terminal repeats (LTRs) (2)
Transcriptional promoter (upstream LTR) and terminator (downstream LTR) Promoter responds to host cell signals and can also be relatively dormant, creating the latent state that is an important characteristic of HIV
HIV entry (3)
Virus may enter through
microabrasions on mucosal surfaces
needle punctures (IV drug users)
intact mucosal surfaces
HIV entry
Virus may enter as (2)
part of an infected cell (macrophage, lymphocyte, spermatozoa)
free virus
HIV replication during the — phase of infection
after burst of viral replication that occurs during — infection
chronic
initial
HIV replication during the chronic phase of infection
after burst of viral replication that occurs during initial infection (2)
Note initial contact is with macrophage lineage cells. Infect/stick to dendritic cells transport to lymph node - contact with CD4 T cells DTH
DTH=delayed-type
hypersensitivity (Type IV hyper.)
-important for controlling (2)
DTH is mediated by
fungal
and intracellular pathogens
(bacterial and viral)
CD4 T cells
HIV
Neurological symptoms
basis is not well understood (2)
- possibly due to viral infection of neurons - possibly release of substances by other cells that promote inflammation in brain
<— CD4 T-cell/mm3 is the
criterion for AIDS.
200
Patients with higher CD4 Tcell counts are also
considered to have AIDS if
they display AIDS indicator
conditions (see next slide).
AIDS-Indicator Conditions (Centers for Disease Control) (7)
Candidiasis of the bronchi, trachea, or lungs
Candidiasis, esophageal
Kaposi sarcoma
Mycobacterium avium complex (MAC) or Mycobacterium kansasii, disseminated or extrapulmonary
Mycobacterium tuberculosis, pulmonary or extrapulmonary
Mycobacterium, other species or unidentified species, disseminated or extrapulmonary
Pneumocystis jiroveci (formerly carinii) pneumonia (PCP)
HIV
Transmission occurs by
direct exposure of persons bloodstream to body
fluid containing virus. HIV is found in the blood, semen, or vaginal fluid of
someone who is infected with the virus.
HIV is not transmitted by
casual contact (touching, etc.) (or even kissing, sneezing, bug bites, etc.)
HIV
There is a risk for health care workers
but
transmission even through
needlestick is poor
(less than 1% of exposures show
seroconversion)
AIDS characteristics (2)
• progressive destruction of CD4+ cells leads to collapse of immune
system
• patient susceptible to opportunistic infections
Central nervous system disease also
associated with AIDS
dementia
AIDS-related cancers
• Kaposis sarcoma
– caused by human herpesvirus 8
HIV
treatment involves:
– antiviral agents (3)
- nucleoside analogue reverse transcriptase (RT) inhibitors
- nonnucleoside RT inhibitors
- protease inhibitors
- Fusion-penetration inhibitors (target gp41)
HIV
Prevention and control
• search for vaccine is ongoing
A recombinant virus assay was used to characterize in detail neutralizing
antibody responses directed at circulating autologous HIV in plasma. Examining serial plasma specimens in a matrix format, most patients with primary HIV infection rapidly generated significant neutralizing antibody responses to early (0-39 months) viruses, Plasma virus continually and rapidly evolved to escape neutralization, indicating that neutralizing antibody exerts a level of selective pressure that has been under-appreciated based on earlier, less comprehensive characterizations. These data argue that
neutralizing antibody responses account for the extensive variation in the envelope gene that is observed in the early months after primary HIV infection.
Plasmid for producing HIV virions from within cultured
cells (only the part of the plasmid encoding HIV is shown)
(4)
- HIV DNA on plasmid is transcribed into HIV RNA.
- HIV RNA is translated into HIV proteins, which assemble
into nucleocapsids. - HIV RNA is also packaged into the nucleocapsids.
- HIV virions are created when the nucleocapsids bud
through the cell membrane.
The HIV DNA on the plasmid lacks the envelope gene
(env), which has been replaced with a luciferase gene.
1. This allows for HIV env genes from the patient serum
samples to be used for creation of —. The
patient env genes are expressed from a second plasmid in
the cells. Because the virions contain separately supplied
env proteins they are called —.
HIV virons
pseudovirions
- The — present within HIV is used to detect
subsequent infection by the — produced in
this study. If cells become infected they will express
—, which is easily detected using a light-based
assay
luciferase
pseudovirions
luciferase
Pseudovirions created
in a
producer cell
Mixing pseudovirions with patient
serum samples:
different combinations
of each were used, representing virus
and antibodies present at different
times in the study
Pseudovirions unaffected by
the antibody incubation will
infect test cells. Infection is
monitored by
luciferase
activity.
Pseudovirions are artificial virions containing —. In this case the envelope proteins (2) come
from viral envelope genes amplified from patient serum samples. A collection of pseudovirions was generated that represented the
HIV population present in each of the monthly serum samples taken during the 39 month study.
altered envelope proteins
gp41 and gp120
HTLV
human T-cell lymphotropic viruses (HTLVs) -I, -II, -III, and -IV
HTLV-I
causes adult T-cell leukemia and lymphoma
HTLV-II, -III, and –IV
no known diseases associated with these viruses
