Transcript Virus-induced immunosuppression

Virus-induced
immunosuppression

Infections usually
stimulate immune
response, but some
infections can cause
global immune
suppression or
specifically dampen
one arm of immune
system
Mechanism
Virus
Host
Degree of
Immunosuppression
Virusspecific
or broad
Attack on one or more cells
of the lymphoreticular
system
HIV
Human
Marked
Broad
LCMV
Marked
Broad
CDV
Mouse
(adult)
Dog
Marked
Broad
Rubella
Human
Moderate
Specific
LCMV
Mouse
Moderate
Specific
Measles
Human
Moderate
Broad
HSV
Human
Mild
Specific
Vaccinia
Human
Mild
Specific
FLV
Mouse
Moderate
Broad
Fetal infection leading
to tolerance
Perturbation of
cytokine homeostasis
and intracellular signalling
Viral proteins acting as
viroceptors or virokines
Suppressor T lymphocytes
Global immunosuppression
during measles infection
8
6
4
INDURATION(m)
Induration (mm)
Induration
(size of reaction
to tuberculin skin test)
2
0
B
A
S
E
R
A
S
H
1
2
3
4
W
E
E
K
S
A
F
T
E
R
R
A
S
H
Mechanisms of
Immunosuppression



Virus infection and depletion of immune
cells (monocytes, T cells, APCs)
Tolerance induction
Perturbation of immune response thru
secreted viral proteins
Virus infection and depletion of immune
cells (monocytes, T cells, APCs)

HIV infection and CD4 T cell
depletion

HIV replicates primarily in
CD4+ expressing T cells



Destruction of T-helper
and T-effector cells by
direct cytopathic and
bystander effects
Insidiously, Ag-specific
CD4+ T cells appear to be
preferentially infected
monocytes/macrophages
and dendritic cells can
also be infected; noncytopathic infection
(reservoirs?)
HIV-specific CD45RO+ CD4+ T cell
CMV-specific CD45RO+ CD4+ T cell
Total CD45RO+ CD4+ T cell
Douek DC et. al. (2002) HIV preferentially
infects HIV-specific CD4+ T cells.
Nature 417:95
PBMCs from HIV+ patients
(2 X 108 cells)
Stimulate with overlapping peptide pools
that span entire HIV proteome
Stimulate with CMV peptides
Ag specific clones will be activated when stimulated by cognate peptide,
and will upregulate CD69 (activation marker) and secrete IFNg
FACS sort for CD3+, CD4+, CD69+, IFNg positive cells
Real-time PCR to quantify the amount of HIV DNA present
Real-time PCR
Taq
F
Q
Primers and probe anneal to target
Taq
Taq begins to displace 5’ end
of probe as extension proceeds
Taq
5’ nuclease activity of Taq cleaves off
5’ fluorophore on probe
Probe begins to fluoresce as it separates
fromQuencher, fluorescence builts up as
PCR products accumulate
Virus infection and depletion of immune
cells (monocytes, T cells, APCs)

HIV infection and CD4 T cell
depletion

HIV replicates primarily
CD4+ expressing T cells


Destruction of T-helper
and T-effector cells by
direct cytopathic and
bystander effects
Insidiously, Ag-specific
CD4+ T cells appear to be
preferentially infected
Mechanism??
HIV-specific CD45RO+ CD4+ T cell
monocytes/macrophages
and dendritic cells can
also be infected; noncytopathic infection
(reservoirs?)
CMV-specific CD45RO+ CD4+ T cell


Total CD45RO+ CD4+ T cell
Douek DC et. al. (2002) HIV preferentially
infects HIV-specific CD4+ T cells.
Nature 417:95
HIV
Direct transfer of virus
captured on cs via DC-SIGN?
MHC Class II
CD4
TCR
DC-SIGN: A Conduit for Transfer
of HIV to Lymphoid Organs?
Geijtenbeek, T.B.H. et al, Cell 100: 594
Virus infection and depletion of immune
cells (monocytes, T cells, APCs)
Alveolar macs
LCMV and APCs
Clone 13 preferentially
infects and destroys
macrophages and DCs

APCs are destroyed first
before cognate antigen
presentation can take place
Armstrong strain is
immunogenic and thus wellcontrolled by responding
immune system
Immune
clearance
Virus titer

Virus titer

Virus titer

Virus infection and depletion of immune
cells (monocytes, T cells, APCs)

LCMV and APCs



Clone 13 preferentially
infects and destroys
macrophages and DCs
Armstrong strain is
immunogenic and thus wellcontrolled by responding
immune system
Clone 13 strain of LCMV is
globally immunosuppressive

Tolerance induction when
newborns are infected
CTL response (lytic unit s) on target cells infected with
Infection with
fection
with
clone 13
at age
Herpes
simplex
Influenza
Vaccinia
LCMV
Immunosuppression
Not infected
ot infected
389
586
4000
16246
None
1 day
378
628
5769
0
LCMVspecific
0
56
159
0
Broad
one 13 at age
< 1 day
6 weeks
weeks
Mechanisms of
Immunosuppression



Virus infection and depletion of immune
cells (monocytes, T cells, APCs)
Tolerance induction
Perturbation of immune response thru
secreted viral proteins
Tolerance Induction:
Virus as Self

Tolerance

Required for prevention of autoimmunity (we are tolerant of
self-antigens)



Thymic deletion of “forbidden” clones; T-cell clones are
“educated” in the thymus during development
Peripheral exhaustion of “forbidden” clones
Characteristic of tolerogenic viral infections




Most easily induced during fetal development
Most readily induced if viral replication produces high levels of
viral antigens
Virus specific
Leads to viral persistence
LCMV and tolerogenic Infections


Neonatal mice infected with
LCMV (clone 13) are tolerant
only to LCMV but responds
well to other viruses
Thymic deletion:

LCMV infects immature
thymocytes; T cells being
educated in the presence of
LCMV expressing T cells in
the thymus are thus tolerant
(LCMV reactive clones are
deleted)
CTL response (lytic units) on target cells infected with
Infection with
fection
with
clone 13
at age
Herpes
simplex
Influenza
Vaccinia
LCMV
Immunosuppression
Not infected
ot infected
389
586
4000
16246
None
1 day
378
628
5769
0
LCMVspecific
6 weeks
weeks
0
56
159
0
Broad
one 13 at age
< 1 day
LCMV and tolerogenic Infections

Peripheral exhaustion of
reactive clones


CTL induction is faster with a higher
viral innoculum but vast majority of
activated CTLs apoptose rather than
self-renew and differentiate into effector
cells
Virus-induced high-dose tolerance
produces virus-specific
immunosuppression
LCMV-tolerized mice still capable of raising
vaccinia-specific response
C TL activi ty, l ytic uni ts (X 1000) pe r sple en
on target cel ls infe cted with
LCMV CMV
(Docile
strain)
Doci
le strain)
102 2PFU
PFU
ot i n fe cted
Not Infected
107 7PFU
PFU
7
PFU
107 PFU
LCMV
Vacci n ia
Virus
Un i nfected
Not i n fe cted
In fe cted
228
ND
ND
31
ND
0.3
Not i n fe cted
In fe cted
<0.2
<0.2
ND
26
<0.2
0.1
Vacci n ia virus
Mechanisms of
Immunosuppression



Virus infection and depletion of immune
cells (monocytes, T cells, APCs)
Tolerance induction
Perturbation of immune response thru
secreted viral proteins
Viral Proteins that perturb
immune responses

Effect on lymphocyte proliferation

Immunosuppressive proteins encoded by viruses that reduce
T cell proliferation (eg. P15e of some retroviral envelopes)
Effect on complement


Accessory proteins encoded by HSV (gC and gI) can prevent
complement activation by binding Fc porion of anti-HSV (gC)
antibodies
Se veri ty of virus-induced lesions
Strain of HSV
Wi l dtype
gI-ne gative
gE-ne gative
Epithelium of
corne a
C orne al
stroma
Brain
(encephalitis)
Se vere
moderate
m ini mal
moderate
none
none
fatal
none
none
Viral Proteins that perturb
immune responses

Effect on lymphocyte proliferation

Immunosuppressive proteins encoded by viruses that reduce T cell proliferation
(eg. P15e of some retroviral envelopes)
Effect on complement

Down-regulation of MHC Class I




MHC Class I essential for Ag presentation of viral-derived
peptides
MHC Class I down-regulation prevents CTL lysis of virus
infected cells
Different mechanisms: HIVnef, Adeno E1A, E3
Viral Proteins that perturb
immune responses




Immunosuppressive
proteins encoded by viruses
that reduce T cell
proliferation (eg. P15e of
some retroviral envelopes)
Effect on complement
Down-regulation of MHC
Class I
Interference with Cytokine
functions

IFN-g receptor homology
(B8R) encoded by
poxviruses blunt effects
of IFN-g secreted by Agspecific T cells
Anti-viral effects of IFNg can be
abrogated by B8R: vesicualr virus
titer in the presence of IFNg +/- B8R
1
0
0
8
0
6
0
4
0
PFU(%CONTROL)
Effect on lymphocyte
proliferation
B
8
R
B
A
C
U
L
O
C
O
N
T
R
O
L
2
0
0
1
1
0
0
8
0
2
3
4
5
4
5
V
A
C
C
I
N
I
A
C
O
W
P
O
X
C
O
N
T
R
O
L
6
0
4
0
PFU(%CONTROL)

2
0
0
1
2
3
M
E
D
I
U
M
(
L
O
G
C
E
L
L
E
Q
U
I
V
A
L
E
N
T
S
)
1
0
Controls: Culture Supernatants from
(1)
Recombinant vaccinia (DB8R8)
(2)
Wt Vaccinia + anti-B8R Ab
(3)
Mock-infected
(B8R)
125I-IFN-g
IFN-gR homolog
IFN-gR
Measure amt of radioactivity bound to cells
In the presence or absence of IFN-gR homologs
Chemical Cross-linking
125I-IFN-g
+ (B8R)
125I-IFN-g


LCMV
Morbilliviruses: Canine
Distemper Virus




Acute febrile & fatal disease in dogs
Encephalitis, pneumonitis, gasteroeteritis
Immunosuppression results in inability to
control bacterial/fungal superinfection
CDV infects lymphocytes, monocytes
resulting in severe leukopenia



Loss of lymphoproliferative
response
Loss of re-call antigen response
Retroviruses:
 MLV/MAIDS
CTL response (% 51Cr release)
Animal Viruses Associated
with Immunosupression
Human Viruses Associated
with Immunosupression
Measles




Lack of lymphoproliferative response
50% decrease in T-cell count
Few monocytes/lymphocytes are actually
infected: immunosuppression must be
indirect
Envelope glycoproteins (F and G proteins)
alone can inhibit T-cell proliferative
response

Binding of F/G complex to measles
virus receptor (CD46) may trigger
intracellular signaling cascades
leading to inhibition

Stimulation Index

T-cells
PHA
proliferation
Expt. and controls?
(DNA synthesis)


Rubella
HV/SIV
3H-thymidine
Stimulation Index: Amt. Radioactivity (+PHA)
Amt. Radioactivity (-PHA)