Download 10mb ppt - UCLA.edu

Immune Responses to Viral
Infection


Non-Specific Responses
(Innate Immunity)



Interferon
Natural Killer Cells
Complement and
“Natural” Antibodies


Specific Responses
(Adaptive Immunity)


Humoral (antibodies)
Cell-mediated (e.g. CTLs)
Interferons

Interferon effects are mostly
indirect



Type I IFNs




Induction of antiviral proteins (e.g Mx)
Augmentation of cellular immune
response (upregulation of MHC Class I)
a, b, , t
Induced by dsRNA, virus infection, IL1/IL-2/TNFa
Produced by all cells
Type II IFNs (IFN-g)



Mediator of Ag-specific response
Induced by IL-12
Produced by T cells, NK cells
Significance of IFN response


“Knock-out” mice
IFN a/b knock-outs (Type I)


IFN g knock-outs (Type II)


Increased susceptibility to most viral infections
Slight increase in susceptibility to some viruses
Interpretation:


Type I is more crucial than Type II IFN response
Type I (secreted by all cells) is essential first line
defense, Type II IFN is only one part of
multicomponent effector immune response
Natural Killer Cells

Large Granular Lymphocytes Type I
(LGL)/NK Cells
IFNs




Perforin (causes membrane
pore formation)
Granzymes (apoptosis)
MHC Class I on target cells
bind to KIR on NK cells and
inhibits NK mediated lysis
Virus Infected Cells

MHC Class I
(late)
MHC Class I
(early)
(Inhibitory)
(Activating)
KIR
Early (MHC Class I
downregulation)


Virus-infected
cell
Sensitive to NK cell lysis
Late (MHC Class I
upregulation)

Resistant to NK cell lysis but
sensitive to CTL lysis
LGL
Non-specific precedes specific
immune responses




IFN secretion
NK Cell response
Effector CTL
Humoral (Ab)
immunity
(LCMV Infection)
Complement and “NaturalAbs

Complement cascade
results in MAC--->cytolysis



Initiated usually by Ag-Ab
complex
Usually, acts as effector
mechanism for adaptive
immune response
May also act as “natural”
antiviral

p15e protein on some
retroviruses binds C1q
and activates complement
cascade without effector
antibodies
p15e
Complement and “Natural” Abs




Gal (a1-->3) Gal
Digalactose moiety not found in humans and Old World primates
due to lack of a1--->3 galactosyl-transferase (a1--->3 GCT)
Viruses grown in other mammalian cells can be neutralized by
human or old-world primate sera (that have never seen the virus)
due to high titer anti- Gal (a1-->3) Gal antibodies
anti- Gal (a1-->3) Gal antibodies are pre-existing “natural”
antibodies

anti- Gal (a1-->3) Gal antibodies responsible for hyperacute rejection
during xenotransplantation (e.g. using pig organs)
Adaptive Immune Response
B cell response
T cell response
Humoral
“Cellul ar”
B lymphocyte
CD8 CTLp
CD4 cytokine p
Plasma cell
CD8 CTL
CD4 (cytokine)
Immu nog lobuli ns (Igs)
Perforins,
gra nzymes,
cytokines
Persistence of effectors
YES
NO
Ana mnestic (memory)
response
YES
YES
Type of immuni ty
Precursor (memory) cell
Effector cell
Mediator molecules
B Cell Responses
IL-4
T Cell Responses
IL-2,
IFN-g
Seeks out virally infected cells
with viral peptides presented in
context of MHC Class I
Antibody Response

Measurement




Effector Functions




Functional (Neutralization titers)
Quantitative (ELISA)
Qualitative (Western Blot)
Viral Coating (inhibition of attachment, infection)
Complement activation
Opsonization (Virus-Ab complex removed by phagocytosis
via Fc rceeptors on macrophages)
Kinetics
Neutralization Ab Titers
12
10
Ctrl Ab
Neut. Ab
PFU/ml
8
6
4
2
0
1/10,000
1/1,000
1/100
50% Neutralization titer
1/10
ELISA
substrate
color
Y Y
Y YYY
HRP
Western Blot
Antibody Response

Measurement




Effector Functions




Functional (Neutralization titers)
Quantitative (ELISA)
Qualitative (Western Blot)
Viral Coating (inhibition of attachment, infection)
Complement activation (Fc portion binds C1q and initiates
complement cascade)
Opsonization (Virus-Ab complex removed by phagocytosis
via Fc receptors on macrophages)
Kinetics
Poliovirus Ab Titer
(Reciprocal)
Kinetics of Ab Response
IgA
--mucosal antibodies
--IgA secreting plasma cells
home into gut via CCR10;
gut epithelium secretes MEC,
which is the ligand for CCR10
--other chemokines can skew Ig
response
Time course and localization of Plasma
Cells (Antibody Secreting Cells)
Serum Ab
Marrow ASC
Ab titer is maintained for
A long while (as opposed to
Ag-specific CD8 effector cells)
Measurement of Cellular Immune Response
ssay
Fresh or
cultured cells
Target cell
or marker
Readout
DA
miti ng dilution
LDA
say)
Cultured
Cell presentin g epitope
bound to syngeneic Class
I MHC
51
TL
CTL
ytolytic T cells)
Fresh
Cell presentin g epitope
bound to syngeneic Class
I MHC
51
etra mer
Fresh
Fluorescent complex
with epitope bound to
syngeneic Class I MHC
FACS (fluore scent
activated ce ll sorter)
Intracellular
ytokine
Cytokine
trace llul ar
Fresh
Fluorescent complex
bound to intra cellular
cytokine
FACS (fluore scent
activated ce ll sorter)
LISPOT
ELISPOT
Fresh
Secreted cytokine
Monocellul ar focus of
released cytokine
Tetramer
Cr release from targe t
cells
Cr release from targe t
cells
Tetramer Staining
Y Y
Y YY Staining using
E (Effector Cell)
CTL
a-perforin Abs
SAV
TCR
HIV-specific
CTL
Viral Antigen
MHC Class I
51Cr
T (Target Cell)
Effector Functions of CD8
Lymphocytes



Perforin and granzyme secretion upon recognition of
Peptide/MHC I complex by TCR
 Perforin:pore formation, cytolysis
 Granzyme: tiggers apoptosis
Cytokine secretion(IFN-g, TNF-a,IL-2)
 Activation induced apoptosis, viral purging(?)
Relative contribution of CTL effector functions to viral
clearance is virus specific
 E.g. clearance of LCMV is CTL dependent, while
clearance of HBV is more cytokine dependent
Wt Mice infected
with HBV
Adoptive Transfer of
CD8+ T cells (CTLs)
HBV Transgenic mice
HBV-speciifc CTLs
can clear HBV in liver
of transgenic mice
Pre-incubation of CD8+ T cells
with anti-IFNg or TNFa abrogates
ability of CTLs to clear HBV
RT-PCR for HBV RNA
Since 100% of hepatocytes (liver cells)
in trasngenic mice carry HBV genome,
clearance of viral RNA obviously cannot
Involve cell death
Kinetics of Cellular Immune Response:
Effector vs Memory T Cells


Effector CTLs
appear rapidly but
wane by 3-6 weeks
post-infection
Memory T cells
persist for life time;
maintained by
homeostatic
proliferation
Neut. Ab Titer
% Paralyzed
Ab response:
Protection against Re-infection
Anamnestic Ab response
Immmunity as host defense


CTL response most important in
controlling primary infection
Ab response most important in
protecting against re-infection