Download M261 MHC class I antigen presentation April 17, 2000

M261
ANTIGEN PRESENTATION/MHC CLASS II
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Pete Sieling
Phone: 825-6964
email: [email protected]
Office: 52-127 CHS
• Reading for Wednesday (4-20) and Friday (4-22)
lectures: Chapter 5 (pp169-198), Janeway et al.
6th edition.
ANTIGEN PRESENTATION
MHC CLASS II
• Importance of dendritic cells to T cell
activation.
• Compare and contrast MHC I and MHC II
peptide binding.
• MHC class II antigen processing and
presentation pathway.
• Mechanisms of immune evasion.
• Cross-presentation.
• CD1 antigen presentation pathway.
• Translational therapies targeting MHC
antigen presentation pathways.
MOLECULES OF T LYMPHOCYTE RECOGNITION
CD8 T-CELL
CD4 T-CELL
a b
TCR ab
CD4
b1
MHC
CLASS II
b
CD3
b2
a1
a
CD8
15 aa
peptide
a2
ANTIGEN PRESENTING CELL
a b
TCR ab
a2
MHC
CLASS I
CD3
a3
a1
9 aa
peptide
b 2m
ANTIGEN PRESENTING CELL
WHAT DISTINGUISHES MHC CLASS I FROM
MHC CLASS II ANTIGEN PRESENTATION?
Expression:
Source of Ag:
T cell co-receptor:
MHC protein:
Salient characteristic:
MHC class I
MHC class II
all nucleated cells
endogenous
CD8
single chain (heavy)
peptide transporter
professional APCs
exogenous
CD4
two chains (a and b)
peptide loading comp.
DENDRITIC CELLS INITIATE T CELL
RESPONSES BY PRESENTING ANTIGENS
TO NAÏVE T CELLS
Text Figure 8.14
TWO SIGNAL HYPOTHESIS OF NAÏVE T CELL
ACTIVATION
(e.g. mature dendritic cell)
TWO SIGNALS ARE
REQUIRED FOR A NAÏVE T
CELL TO BECOME
ACTIVATED, OTHERWISE
ANERGY
(UNRESPONSIVENESS) IS
INDUCED
CONSERVATION OF STRUCTURE IN MHC
MOLECULES AND PEPTIDE-BINDING GROOVE
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The a1 and a2 portions of MHC class
I and a1 and b1 of MHC class II form
mirror images of each other to
create the peptide binding groove.
Despite modest sequence homology,
MHC class I and II have evolved to
create similar, though not identical
binding grooves from a single chain
(MHC I) or two chains (MHC II).
STRUCTURE OF MHC MOLECULES AND
PEPTIDES BOUND TO THE GROOVE
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•
MHC class I molecules bind 8-10 amino acid peptides whereas MHC class II
bind 12 or longer peptides.
MHC class II more promiscuous about length of peptide bound.
Mouse H2Kb
Mouse I-Ak
Human HLA-DR3
STRUCTURE OF MHC MOLECULES AND
PEPTIDES BOUND TO THE GROOVE
MHC class I
+ peptide
MHC class II
+ peptide
MHC CLASS II ANTIGEN PROCESSING
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MHC class II molecules present antigens taken up by the cell through endocytosis.
MHC polypeptides (a and b) are synthesized on ER and are chaperoned to a
specialized antigen loading compartment by invariant chain (Ii); invariant chain
serves two purposes, it functions as a chaperone and occupies the peptide binding
groove to stabilize MHC class II and prevent other peptides (self) from binding until
MHC arrives in the loading compartment.
Invariant chain is cleaved by acid proteases until it leaves only the peptide-binding
portion (CLIP) in MHC.
Endocytosed antigens are also cleaved by acid proteases; low pH requirement for
proteases to become activated.
HLA-DM catalyzes the removal of CLIP and binding of antigenic peptide.
pH 7
Text Figure 5.10
pH 5
pH 5
pH 5
THE ROLE OF PROTEOLYSIS IN MHC
CLASS II PRESENTATION
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Proteolysis for MHC class II antigen presentation occurs in
endocytic vesicles by proteases that are active at low pH.
Cysteine proteases such as the cathepsins degrade
proteins into short peptides for MHC class II presentation.
Invariant chain is also degraded by cathepsins into CLIP.
THE ROLE OF CATHEPSINS IN MHC CLASS
II ANTIGEN PRESENTATION
• Cathepsin L is especially
important in thymic
epithelial cells, which
present antigen for
positive selection of
thymocytes.
• Cathepsin S seems to be
especially important in B
cells and dendritic cells,
less so for macrophages.
Nakagawa et. al.,
Immunity 10:207, 1999
I-Ab
Ii
CLIP
Nakagawa et. al.,
Science 280:450,
1998
ROLE OF HLA-DM IN THE MHC CLASS II
PATHWAY
Sloan, et. al., Nature 375:802, 1995
• HLA-DM facilitates the
removal of CLIP and
binding of antigenic
peptide into the MHC class
II binding groove.
• HLA-DM activity is pHdependent.
Biotinylated
peptide
b1
a1
b2 a2
MHC class II
b1
Protein concentration
Streptavidin
fluorescent tag
a1
b2 a2
HLA-DM or
control protein
Anti-MHC in
microtiter plate
Fluorescence measurement
pH
MHC CLASS II PROTEINS ARE LOADED
WITH PEPTIDE IN A SPECIALIZED
ENDOCYTIC COMPARTMENT (MIIC)
• MHC class II proteins are enriched in multilamellar vesicles called
MIICs (MHC class II compartments) that are distinct from other
intracellular vesicles.
MHC class II
Late
endosome
Tulp et. al., Nature
369:120, 1994
Early
endosome
Amount (arbitrary units)
12
Lysosomes
Plasma
membrane
lysosome
10
MHC class II
8
particle
6
4
Golgi
2
ER
0
0
5
10
15
20
Fraction number
Text Figure 5.9
MECHANISMS OF IMMUNE EVASION (MHC
CLASS II)
• Mycobacteria prevent
acidification of
endosomes.
• Inhibition of acidification
will prevent proteases
from being activated.
• Without proteases,
mycobacterial proteins
won’t be processed or
loaded into MHC class II.
Mycobacteria
Control
Leishmania
Control
Sturgill-Koszycki, et. al.,
Science 263:678, 1994
pH
HOW DO NAÏVE CD8 T CELLS BECOME
ACTIVATED WHEN THE INFECTED CELL IS NOT
A PROFESSIONAL APC?
BONE MARROW CHIMERAS
•
Used to determine the function of
certain immune cells of one
background against the nonimmune cells of another
background. Irradiate recipient
mouse (kills hematopoietic cells
from which immune cells are
derived) and inject bone marrow
cells from donor mouse. In this
way, you populate a mouse of
one genetic background with the
immune system from a mouse of
another genetic background.
CROSS PRESENTATION
• CTL immunity to virus-infected non-hematopoietic cells
requires presentation of exogenous antigen. Question
addressed: Do non-hematopoietic cells infected with virus
activate CTLs to kill infected cells or do hematopoietic cells
take up exogenous peptides from environment, present them
to T cells?
gPVR
gPVR-expressing
cell (recipient)
Polio-OVA
Peptides
Hematopoietic
cell (donor)
Sigal, et. al., Nature 398:77-80, 1999.
CONTROL OF CROSS PRESENTATION BY
THE MHC CLASS I CYTOPLASMIC DOMAIN
Transfected
fibroblasts/CTL
Transgenic mice
Lizee, et. al., Nature Immunol 4:1065-1073, 2003.
ER-PHAGOSOME FUSION CREATES A
CROSS PRESENTATION COMPARTMENT
OVA
Guermonprez, et. al., Nature 425:397-402, 2003
TAP2
MHC class I
CROSS PRESENTATION PATHWAY
Houde, et. al., Nature 425:402-406, 2003.
THE POWER OF MHC TETRAMERS
• MHC heavy chains are
engineered with linker to
create tetramer.
• Peptide is added in solution
or engineered to covalently
bind to MHC binding groove.
• HLA-A2 tetramers are labeled
with a fluorescent tag that
allows one to use flow
cytometry to determine the
frequency of antigen-reactive
T cells; previously this was
evaluated by limiting dilution
analysis.
Altman, et. al.,
Science 274:94, 1996
HLA AND DISEASE ASSOCIATION
• Some diseases are
associated with
specific MHC
alleles, though the
role that MHC plays
in the disease isn’t
clear.
MOLECULES OF T-LYMPHOCYTE RECOGNITION
CD4 T-CELL
a b
CD4
CD3
a b
TCR ab
CD8
CD3
a b
MHC
CLASS I
b 2m
ANTIGEN PRESENTING CELL
CD3
TCR ab
TCR ab
9 aa
peptide
15 aa
peptide
MHC
CLASS II
T-CELL
(ALL PHENOTYPES)
CD8 T-CELL
lipid
CD1
b 2m
DIFFERENT CD1 MOLECULES TRAFFIC TO
DISTINCT INTRACELLULAR LOCATIONS IN
HUMAN DC
CD1
LAMP
CD1+LAMP
CD1a
CD1b
CD1c
Sugita, et al.
Immunity
2000
Sugita, et al
Traffic 2000
MYCOBACTERIAL ANTIGENS THAT
ACTIVATE CD1-RESTRICTED T CELLS
Mycobactin
CD1a antigen
Mycolic
acid
Phosphatidylinositol
mannoside
Glucose
monomycolate
Mannosyl-b1phosphoisoprenoid
CD1b antigens
CD1c antigen
EXAMPLES OF MHC II EPITOPES THAT
REQUIRE PROCESSING IN DISTINCT
SUBCELLULAR COMPARTMENTS
Antigen:
Early Endosome:
MIIC:
46-61
-

35-45

-
116-129

-
17-31

-
308-319
-


-
HEL (Zhong et al. 1997)
S. pyogenes M5 (Delvig et al. 1998)
Influenza Virus (Pinet et al. 1998)
HA H3 307-318
TRANSLATIONAL
THERAPIES TARGETING
MHC ANTIGEN
PRESENTATION PATHWAYS
CD4+
T-CELL 1
TCR
CD4
LATE ENDOSOME/
LYSOSOME/M II C
Ag
Classical Pathway
Alternative Pathway
MHC II
?
EARLY
ENDOSOME
?
?
GOLGI
M II C
TCR
CD4+
T-CELL 2
TRANSLATIONAL THERAPIES TARGETING MHC
ANTIGEN PRESENTATION PATHWAYS
Leader
Ag
LAMP-1
Immunize with DNA
Measure
immunological
functions
Challenge with
microbial pathogen and
measure survival
% survival
120
100
IFN-g
IFN-g
80
CD4
Unimmunized
60
Immunized
40
Unimmunized
20
CD4
Immunized
0
0
5
10
15
Time (weeks)
20
25
CD8+ T-CELL
TCR
MHC CLASS I
PATHWAY
CD8
Ag
PROTEOSOME
CD4+
T-CELL
TAP
TCR
ER
MHC CLASS I
M II C
CD4
MHC CLASS II
pH<5
GOLGI
Ag
MHC CLASS II
PATHWAY
ENDOSOME