HTLV-1 Flashcards
(156 cards)
1
Q
How is HTLV-1 transmitted?
A
breastfeeding; sexual contact; blood transfusion
2
Q
What type of virus is HTLV-1?
A
complex human retrovirus
3
Q
What is the result of HTLV-1 infection for >90%?
A
asymptomatic
4
Q
Waht are the clinical manifestations of HTLV-1?
A
adult T-cell leukaemia/lymphoma ; chronic inflammatory disease of the nervous system
5
Q
What are the symptoms of HTLV-1- associated myelopathy?
A
spasticity/weakness of the legs; hyperreflexia; bladder dysfunction; lumbar pain; constipation; impotence
6
Q
What is the median survival of patients with adult t-cell leukaemia?
A
<1 year
7
Q
What is the closest correlate of risk of disease with HTLV-1?
A
proviral load
8
Q
What are the 2 routes of replication?
A
infectious route via RT; mitotic route via host cell polymerase
9
Q
How does HTLV-1 get passed around in the infectious route?
A
not via free cell particles, but directional cell-cell spread via vriological synapse triggered by cell contact
10
Q
What is the main route by which HTLV-1 persists in the host?
A
mitotic route ( when cell divides, provirus is replicated)
11
Q
What suggests that mitotic route is main persistance route for HTLV-1?
A
get oligoclonal bands, not polyclonal bands detected on southern blot—small number of HTLV-1 clones as mitotic route doesn’t use RT
12
Q
What suggests that HTLV-1 is latent in vivo?
A
virions; viral mRNA and proteins are usually undetectable in fresh PBMCs
13
Q
What is the effect of CTLs on HTLV-1?
A
reduce the proviral load and risk of -HAM– granzymes and perforin are higher in patients with low proviral load; anti-tax CTL avidity correlates with low proviral laod and expression
14
Q
What are CTLs mainly directed against in HTLV-1?
A
Tax
15
Q
How can HTLV-1 escape CTLs?
A
through spontaneous Tax mutations
16
Q
What mutations are associated with protection against HTLV-1 in s. Japan? Why?
A
HLA-A2 and -Cw08–present peptides to CTLs ( further evidence of importance of this cell type)
17
Q
What is the difference between the CTL responses generated by Tax and HBZ?
A
Tax- strong, persistently activated CTL response vs HBZ which is a weak CTL immunogen
18
Q
what is the equivalent of tax in HIV?
A
tat
19
Q
What is the function of Tax protein and HBZ?
A
drive proliferation of hte infected cell
20
Q
What aspect of hte CTL response determines the host ability to control the proviral load efficiently?
A
response to HBZ (all hosts respond to Tax- reponse has no correlation with proviral laod)
21
Q
What is the importance of HLA genotype in protection against HTLV-1?
A
possession of strong HBZ-binding alleles prevents aroudn 50% of potential cases of HAM in Japan; by looking at the strength of HBZ binding alone you can correctly classify 55% of cases of HAM
22
Q
What cells does HTLV-1 infect?
A
CD4 t cells
23
Q
What determines a T cell clones abundance and pathogenicity?
A
genomic integration site- as it regulates switch between proviral latency and expression
24
Q
What defines a clone?
A
the unique genomic integration site of hte HTLV-1 provirus
25
How does clonality correspond to proviral load?
proviral load is correlated with total number of clones but not with oligoclonality
26
How many proviral copies do HTLV-1 infected cells carry?
one
27
How many HTLV-1 T cell clones are there in an asymptomatic carrier?
10,000
28
how many HTLV-1 T cell clones are in a patient with HAM?
30,000
29
what is the pathogenic significance of oligoclonal proliferation?
none
30
How does HTLV-1 integrate?
targets specific transcription factor binding sites
31
What is the difference between expression of HBZ and tax?
HBZ is persistently expressed- at low levels but tax is frequently silent - some clones express lots of tax but not all
32
On what strand is HBZ?
- strand
33
What strand is tax found on?
+ strand
34
Why is HBZ more important than tax in terms of immune repsonse?
anti-tax cells will only target some infected cells but antiHBZ targets all infected cells
35
What is foudn at the 3' end of hte HTLV provirus?
selectively unmethylated
36
What creates the chromatin loops?
CTCF protein which bind at 2 loci, dimerize and then form a loop
37
Waht is the function of chromatin loops?
regulate promoter-enhancer contacts
38
What is the effect of HTLV-1 on CTCF?
CTCF can bind HTLV-1 provirus which can cause dimerisation in the wrong place forming abonromal loops
39
What can abnormal chromatin looping cause?
increases risk of insertional oncogenesis- proviral CTCF site makes long-range interactions with host chromatin brinding viral enhancer near host genes
40
What genes are over-expressed in individuals with HAM?
interferon-stimulated genes; p53 signalling
41
How is HBZ implicated in leukaemia?
persistent clonal proliferation--replicative mutations
42
What are the 2 mechanisms of insertional mutagenesis with HTLV-1?
local- flanking provirus; distant- via chromatin looping
43
How is Tax implicated in leukaemia?
acceleration into mitosis; inhibits DNA repair and promotes genome instability
44
What does HBZ stand for?
HTLV-1 basic zipper factor
45
What genus and subfamily does HTLV-1 belong to?
deltaretrovirus; orthoretrovirinae
46
Which host genes does Tax transactivate?
IL-2 receptor a chain (CD25); IFNy and ICAM1
47
What mediate the cell-to-cell contact which allows HTLV-1 spread?
ICAM1 on infected cell to LFA-1 on target cell
48
What is the specialised structure which transmits budding of the virus towards the cell contact area?
virological synapse
49
What happens when HTLV-1 is expressed in a cell?
the cell becomes activated- large and irregularly shaped with upregaulted ICAM1
50
When does the HTLV-1 pre-integration complex gain access to the host genome?
when the nuclear envelope dissassembles during mitosis
51
What are the 2 stages in pathology in HAM?
first- inflammatory phase and then neurodegerative phase
52
What is seen in the initial inflammatory phase of HAM?
perivascular lymphocytic infiltration
53
which coutnires have the highest numbers of HTLV-1 infected individuals?
Japan and Brazil
54
Where are the inflammatory infiltrates of mononuclear cells found most frequently?
upper thoracic spinal cord
55
What is the makeup of the mononuclear infiltrate in HAM?
CD4 predominate in early active lesions with the proportion of CD8 cells increasing progressively as the lesion progresses
56
How is HTLV-1 proviral load measured?
number of HTLV-1 DNA copies per peripheral blood mononuclear cell
57
What happens to the proviral load after the acute phase of infection?
reaches a stable value- set point
58
What determines the set point proviral load?
quality of that individuals T cell response to the virus
59
Why is proviral load not the only factor in HAM?
50% of asymptomatic carriers have proviral loads of >1% which is when the exponential increase in prevalence of HAM occurs
60
What is the most common TLV-1 genotype worldwide?
A
61
What does the HLA class I genotype of an individual determine?
the specificity and efficacy of their CD8 T cell repsonse to a virus
62
When is hte peak incidence of HAM in age?
fifth decade of life
63
Which gender is more susceptible to HAM?
femailes (4:1 in US)
64
why is IFNy thought to play a pathogenetic role in HAM?
HTLV-1 Tax protein induces a Th1-like state and IFNy expression in einfected CD4 T cells
65
What is the effect of type I IFNs a and b on HTLV1?
impair HTLV-1 replication
66
What is the abundance of HTLV-1 specific CTLs proportional to?
HTLV-1 proviral load
67
What suggests that HTLV-1 is not latent in vivo but is expressed persistently or at frequent intervals?
CTLs are chronically activated
68
what suggests that CD4 cells are important in HAM?
HTLV-1 infected CD4 cells secrete IFNy and predominate early in HAM lesions; frequency of IFNy secreting CD4 cells is higher in HAM pts than in asymptomatic carriers with a similar proviral load
69
What is a possible mechanism for tissue damage in HAM?
IFNy secreted by infected CD4 cells causes astrocytes to secrete CXCL10 which recruits more cells, reuslting a high local conc. of IFNy and neural damage
70
what other cell type is implicated in HAM?
FOXP3 cells
71
What causes the high frequency of FOXP3 cells in HAM?
HTLV-1 Tax protein
72
How does Tax increase FOXP3 cells?
induces Cd4 t cells to produce chemokine CCL22 which prolongs durvival of Tregs by binding to CCR4 which is characteristically expressed on Tregs
73
Why does HTLV-1 increase Tregs?
Tregs impair the efficiency of the CTL response to HTLV-1
74
What is the effect of antibodies against HTLV-1?
reduce the efficiency of HTLV-1 transmission by breastfeeding; reduce propagation in mice models
75
Waht is thought to be the mechanism behind HAM developmnet?
neurons and glial cells are damaged by toxic or inflammatory products released from the HTLV-1 infected T cells and the repsonding CTLs prsent
76
What are flower cells?
HTLV-1 infected lymphocytes with a characteristic mulilobular nuclei
77
What were the only clinical correlates of the diagnosis of HAM in a Japanese study?
brisk patellar tendon relfelxes and presence of flow cells
78
What is hte median time from onset to use of a unilateral walking aid?
6 years
79
What are correlates of a fasster HAM disease progression?
older age at onset (>50 years); high proviral load
80
What is required for diagnosis of HAM?
detection of HTLV-1 antibodies
81
how should a psotivie HTLV-1 ELISA be confirmed ?
thourhg western blot analysis or detection of viral nucleic acid
82
Why is there a high concentration of beta2 microglobulin in patietns with HAM?
reflects high freq of Cd8 cells (beta2 microglobulin is bound MHC-I to the cell
83
What drugs form the mainstay of HAM treatment?
PO/IV steroids
84
Why might there be a lack of goof results with pharmacological studies of HAM treatment?
tx is started in the late phase of hte disease when infalammation has subsided-- clinical trials should take into account the pahse of the illness
85
What receptor, not HLA enhances HLA class I mediated protection in HTLV1?
KIR2DL2
86
why are biomarkers for HAM important to develop?
can lead to more accurate diagnosis and prognostication; as well as allowing clinical trials to assess treatment effects faster as HAM is very slow progressing
87
What chemokine receptor is expressed on a majority of HTLV infected T cells?
CCR4
88
What are teh cellular receptors for HTLV-1?
neuropilin-1 and GLUT1
89
What are the 4 factors which govern HTLV-1 integration?
integration is mainly in open, transcriptionally-active chromatin; places where certain proteins eg STAT1 are bound; protien phosphatase 2A binds the integration complex; targetd to a primary DNA sequencce motif
90
Why does increasing the number of infected cells in the host augment transmission of HTLV1?
transmits through cell-to-cell contact, therefore transmission needs living infected cells
91
Why is breast-milk and semen infectious with HTLV1?
HTLV1 increases the migratory capacity of infected T ells into the breast milk and semen for transmission
92
What are the 2 broad viral strategies for HTLV1?
host cell prolioferation and cellular motility
93
What 2 regulatory genes does HTLV1 have?
tax and rex
94
What is the only gene found on the minus strand of the provirus?
HBZ - transcribed frmo the 3' LTR
95
Which type of transcription is Tax able to heavily influence?
from the 5' LTR (sense transcripts)
96
What protein is critical for the constant expression of HBZ?
SP1
97
What other protein enhances the trnascription of HBZ by cooperating with SP1?
JunD
98
What suggests that CTLs suppress Tax expression?
when CD8 cells are removed in vitro Tax expression increased
99
Why does mitotic replication generate much less sequence diversity than infectious replication?
mitotic route uses DNA Pol2 rather than RT
100
What is the relationship between clonality and proviral load?
it is the clonal diversity not that degree of oligoclonal proliferation that correlates with proviral load
101
Which cell type are infected with 95% of the HTLV1 proviral load?
CD4 T cells
102
What type of cell does HTLV2 mainly infect?
CD8
103
What is the equivalent of HBZ in HTLV2?
APH-2
104
Waht is the equivalent of Tax in HTLV2
Tax-2
105
What is the function of SAMHD1?
limits the supply of nucleoside triphosphates for virion replication, inhibits HTLV1 infection of macropahges
106
What is the function of APOBEC3G in HTLV1 infection?
generates nonsense mutations but targets the plus strand genes so spares HBZ, this sustained expression of HBZ may favour viral persistence
107
How does HTLV1 reduce type I IFN production?
induces the cytokine suppressor SOCS1 and Tax-mediated inhibition of RIG1 and MDA5
108
which IFN does Tax induce?
IFNy
109
What demonstrates that HTLV1 is persistenyl expressed in vivo?
HTLV1 infected pts have high freq of persistently activated HTLV1 specific CTLs- indicates recent exposure to newly synthesised viral antigen
110
What enhances the protective and pathogenic effects of HLA class I alleles in HTLV1?
KIR2DL2
111
what type of cell is much higher in patients with HAM than in asymptomatic carriers?
HTLV-1 specific CD4 cels
112
Which cytokine does Tax induce CD4 cells to secrete?
CCL22
113
How does Tax maintain a high freq of CD4 FOXP3 cells?
induces secretion of CCL22, CCR4 which is the receptor for CCL22 is found on FOXP3 cells
114
How does HTLV1 mainly increase the proviral load?
driving proliferation of infected cells- mitotic division
115
What indicates the de novo infection does not contribute significantly to the proviral load in the chonic phase?
RT inhibitors and integrase inhibitors don't change the proviral load in HTLV-1 infected individuals
116
How does HBZ inhibit apoptosis of hte infected cells?
perturbs the location and function of FoxO3a which is a transcriptional activatro for genes encoding Bim and Fas ligand; interacts with the Rb/E2F-1 complex; its RNA which stays in the nucleus inhibits apoptosis
117
How does HBZ change the immunophenotype of infected cells?
induces cell surface expression of TIGIT and CCR4
118
How does Tax inhibit apoptosis?
activates NFkB which leads to expression of anti-apoptotic gene c-FLIP
119
How does Tax promote vell proliferation?
activates PI3K/Akt
120
What protein is thought to play a role in the differential expression of plus and minus strands ?
CTCF
121
What is the normal function of CTCF?
form chromatin loops- organise the chromatin structure and to bring enhancers near their cognate promoters
122
Why will each infected T cell clone have its own characteristics of proviral expression?
the genomic integration site influences the expression of the provirus - whichi s unqie to each clone
123
What happens when a host promoter is in the same trancriptional sense upstream of hte 5'LTR?
transcriptional silencing of hte HTLV1 plus strand
124
What happens when a host promoter is upstream of the 3'LTR (same sense as the proviral negativ strand)?
activation of plus strand expression
125
The immune system puts a constant pressure on the virus selecting for clones withan optimal pattern of proviral expression, what is this expression?
minimal but persistent HBZ expression, and bursts of plus-strand expression that may be driven by cellular stress
126
What is the function of the plus strand being expressed during cellular stress?
cellular stress eg when lymphocytes are transferred between individuals, so expression would promote viral transmission
127
Why was Tax thought to be necessary and suggicient for malignant transformation of HTLV1 infected cells?
transduction of Tax-expressing vectors can immortalise T cells in vitro; transgenic expression of Tax induced cancers in vivo- different cancers based on the promoter causing Tax expression
128
What suggests that Tax is not as important in oncogenesis as previously thought?
half of ATL cells dont express Tax whereas all ATL cells express HBZ
129
What are the 3 mechanisms to inactivate Tax expression?
nonsense mutations of hte tax gene; DNA methylation of hte 5'LTR; deletion of hte 5'LTR
130
Why is transcription of the sense strand finally silenced during the natural course of infection?
DNA methylation of hte 5'LTR naturally accumulates
131
What role may CTCF play in preventing methylation of the 3'LTR?
CTCF binding region in pX region which may account for the arrest of DNA methylation before pX and 3'LTR
132
What suggests taht multiple genetic and epigenetic alterations are needed for ATL?
long latent period is necessary before onset of ATL
133
Where are the genetic alterations foudn in ATL cells generally foudn?
in the genes assocaited with pathways that Tax and HBZ infect-- clones persistent and proliferate by actions of Tax and HBZ during carriage thereafter genetic and epigenitc alterations fix or potentiate these changes
134
Give an example of a mutation found in 20% of ATL cells in a HBZ targeted pathway?
gain of function mutation in CCR4 (HBZ induces expression)-increased migration and proliferation of infected cells
135
What genetic mutation is involved in the Tax pathway?
expression of miR31 enhances NFkB in ATL cells even in the absenec of Tax
136
What are the 4 subtypes of ATL?
acute; lymphoma-type; chronic and smouldering
137
How does HBZ induce CCR4 expression?
enhanced GATA3 trancription
138
What receptor promotes viral entry but isn't bound by the env proteins?
heparan sulphate proteoglycans
139
What is the function of Rex?
regulation of nuclear RNA export
140
How did most patients with ATL get the virus?
breastfeeding transmission
141
How does the genotype of HTLV-1 differ between pts with ATL or HAM and asympatomatic carriers?
no difference
142
How does the NK response to HTLV1 differ between pts with HAM and asymptomatic carriers?
frequency of and lytic activity of NK cells was significantly lower in patietns with HAM
143
What is thought to be the mechanism behind using AZT and IFNa to treat chronic ATL?
antiproliferative rather than antiviral
144
What mainly determines whether a host will have a high or low quality CTL response?
host genotypes at the HLA-I and KIR loci and therefore the ability to present epitopes from the HBZ antigen to CTLS
145
what proteins suppress Tax activity?
Wnt transcription factors TCF1 and LEF1
146
What can stop the suppression of Tax activity by TCF1 and LEF1?
T cell activation
147
What genes are overexpressed in models with trangenic expression of Tax?
NFkB pathways genes
148
How does Tax affect NFkB?
directly binds to IKKy and p100, alters the ubiquitination of TRAF6 etc (regulatory proteins)
149
How does Tax induce genetic instability?
thourhg the generation of reactive oxygen species
150
How does HbZ minimise the effect of repeated mitosis on cellular aging ?
enhances expression of the host genes telomerase reverse transcriptase and JunD
151
What infection increases the number of TLV1 clones in a host?
Strongyloides stercoralis
152
Is there an integration spot associated with ATL?
no, but there is evidence that integration close to host genes that frequently dysregulated in otehr leukaemias occurs more frequently than by chance
153
What determines the rate of spontaneous Tax express ion in a given clone?
influenced by the genomic integration site of hte provirus- distance and transcriptional orientation of hte provirus relatige to the nearest host gene
154
Which clones express Tax more frequently?
lower-abundance clones
155
What does CTCF stand for?
CCCTC-binding factor
156
What animal virus is closely related to HTLV1?
bovine leukaemia virus
