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ANTIGEN PRESENTATION
Lymphocyte subsets
CLP
T CELLS
B CELLS
Common
lymphoid
precursor
T
Th
Activate B cells
and macrophages
T HELPER CELLS
CTL
Kill virusinfected cells
CYTOTOXIC T
LYMPHOCYTES
B
PC
Produce antibodies
PLASMA CELLS
RECOGNITION
EFFECTOR CELL
Plasma cell
B-lymphocyte
BCR + antigen
cytokines
Cytotoxic Tlimfocyte (Tc)
Antibody production
Cell killing
TCR + peptide + MHC-I
Effector cell retains specific
receptor
cytokines
Helper Tlymphocyte (Th)
TCR + peptide + MHC-II
Effector cells secrete cytokines
Macrophage activation
Lymphocyte activation
Inflammation
RECOGNITION OF EXOGENOUS AND ENDOGENOUS
ANTIGENES BY T-LYMPHOCYTES
Tc
Th
Exogenous Ag
Endogenous
Ag
Peptides of endogenous proteins
(virus, tumor) bind to class I MHC
molecules
Peptides of exogenous proteins (toxin,
bacteria, allergen) bind to class II MHC
molecules
The number of different T cell antigen receptors
is estimated to be
1,000,000,000,000,000 (1015 - 17)
How can 6 invariant molecules have the capacity to
bind to 1,000,000,000,000,000 different peptides?
A flexible binding site?
A binding site that is flexible enough to bind any peptide?
At the cell surface, such a binding site would be unable to
• allow a high enough binding affinity to form a trimolecular
complex with the T cell antigen receptor
• prevent exchange of the peptide with others in the extracellular milieu
A flexible binding site?
A binding site that is flexible at an early, intracellular stage of maturation
formed by folding the MHC molecules around the peptide.
Venus fly trap
Floppy
Compact
Allows a single type of MHC molecule to
• bind many different peptides
• bind peptides with high affinity
• form stable complexes at the cell surface
• Export only molecules that have captured a
peptide to the cell surface
MHC molecules
• Adopt a flexible “floppy” conformation until a peptide binds
• Fold around the peptide to increase stability of the complex
•The captured peptides contribute to the stabilization of the
complex
• Use a small number of anchor residues to tether the peptide
- this allows different sequences between anchors
and different lengths of peptides
WHERE PEPTIDE BINDING OCCURS?
INTRACELLULAR COMPARTMENTS ISOLATED BY MEMBRANSE
1) cytosol 2) vesicular system
THE ENDOGENOUS ANTIGEN PROCESSING PATHWAY
Tc-cell
MHC-I +
Ag peptide
MHC-I +
self peptide
α-chain+β2m
cytoplasm
citopla
zma
FLEXIBLE
MHC+peptide
CLOSED
Golgi
MHC-I, LMP2/7, TAP
ER
TAP1/2
α-chain
gp96 calnexin
IFN induced coordinated
expression
SELF
PROTEIN
Proteasome
LMP2/LMP7
ANTIGEN
CYTOSOL-DERIVED PEPTIDES ARE
PRESENTED BY MHC-I FOR T-CELLS
Degradation of endogenous proteins in
(immune) proteasomes
TAP: Transporter associated
with antigen processing
Transporters associated with
antigen processing (TAP1 & 2)
Hydrophobic
transmembrane
domain
Lumen of ER
Peptide
ER membrane
Cytosol
Peptide
Peptide
Peptide antigens
from proteasome
ATP-binding cassette
(ABC) domain
Transporter has preference for longer than 8 amino acid peptides
with hydrophobic C termini.
PEPTIDE-MHC INTERACTION IS SUPPORTED BY MULTIPLE
PROTEINS IN THE ENDOPLASMIC RETICULUM
TRIMMING OF PEPTIDES FOR OPTIMAL SIZE
BY BY ERAP
THE EXOGENOUS ANTIGEN PROCESSING PATHWAY
Th-cell
MHC-II +
Ag peptide
MHC-II +
self peptide
CLIP
DMA/B
Ii+αβ
MCII
CLIP
DMA/B
C IIV
Golgi
li
li
MHCII
ER
FLEXIBLE
CLOSED
INVARIANT CHAIN (Ii)
1. Chaperone – conformation
2. Inhibition of peptide binding
3. Transport/retention
DMA/DMB
1. Support the peptide receptive
conformation
2. Exchange of CLIP for
exogenous peptides
THE INVARIANT CHAIN PROTECTS THE MHC CLASS II
BINDING SITE UNTIL REACHING THE APPROPRIATE
COMPARTMENT
DMA/DMB
INVARIANT CHAIN LÁNC (Ii)
1. Chaperon – Conformation
2. Inhibition of the peptide binding
site
3. Transport and retention
1. Stabilization of peptide accessable
conformation
2. Exchange of CLIP to peptides
derived from exogenous proteins
GENERATION OF MHC – I EPITOPES
GENERATION OF MHC – II EPITOPES
HLA-DR1/HLA-DR4
Viral protein
B35
A2
C42
B27
HLA-DQ2/HLA-DQ7
HLA-A,B,C binding
Overlapping peptides
The Tc response is focused to few
epitopes
The Th response is directed to
overlapping epitopes
ENSURE RECOGNITION OF MANY
PATHOGENIC PROTEIN
ENSURE RECOGNITION OF ALL
PROTEINS
TARGETS OF EPSTEIN-BARR VIRUS-SPECIFIC
Tc (CTL) RESPONSES
LATENT ANTIGENS
+
LMP2
± (?)
EBNA5
±
EBNA2
++
++
++
EBNA3 EBNA4 EBNA6
-
+
EBNA1
LMP1
Nhet C W W W W W W H F QU PO M S L E ZR K B G D
W WW W W Y
LYTIC ANTIGENS
BHRF1
++
BMLF1 BZLF1
BMRF1 ++
++
A Nhet
TXV I
BARF0
++
• A poliklonális CTL válasz elsősorban a litikus antigének és az
EBNA3,4,6 nukleáris fehérjék ellen irányul
• Erősen fókuszált egy adott MHC - peptid kombinációra
• Az endogén EBNA1 nem processzálódik és így nem ismerhető fel
Bound peptide
Generation of
peptide
MHC class I
MHC class II
source
self or foreign proteins
self or foreign proteins
size
8-10 amino acids
13-21 amino acids
heterogenity
limited
overlapping set of peptides
natural
cytoplasmic and nuclear proteins
~70% MHC derived,
membrane and extracellular proteins
site
cytoplasm
vesicles, endo/lysosomes
enzyme
proteasome
LMP-2, LMP-7 regulatory subunits
vesicular acidic proteases
cathepsins
transport
TAP - size and C-terminal dependent
cytoplasm  ER
no
no
Ii - target, retention
ER  vesicular system
special compartment
site
ER
vesicles, CIIV
chaperons
calnexin, toposin
Ii - CLIP, DMA/B
stable complexes reflecting the
endogenous environment of the cell
few instable empty molecules
stable complexes reflecting the
exogenous/endogenous environment of
the cell
few re-circulating molecules
complexed with CLIP
MHC transport
MHC - peptide
interaction
MHC - peptide
complexes In
the cell surface
REGULATION OF CLASS I AND II MHC MOLECULES
IFNg
TNF
a
a
b
JAK1
TRADD
TRAF
JAK2
p65 p55 IKK
P
IFNγ
JAK1
IFNγR
P–Y
Ik B
b
IFNgR
TNFRI
JAK2
P–Y
P
Y–P
P– Y
Y–P
P– Y
p65 p55
STAT-dimer
STAT-dimer
Y–P
P– Y
NFkB
A
IRF-1
Y–P
P– Y
Y–P
P– Y
IRF-1
Co-a ktivátor
Y–P
p58 P– Y
ISRE
CIITA
B
W/S
CAAT TATA
RFX X2b p NF-Y
X1
MHCI
X2
Y
CCAAT TATA
MHCII
Type II immune IFNγ increases MHC expression
Inflammatory cytokines and IFNγ induces MHC class II expression in certain tissue cells
(endothelial, astrocyte, microglia)
Co-ordinated upregulation of MHC-I, TAP, LMP and MHC-II, DM, Ii
B-cell
T-cell
Appearance of antigen
Soluble, particles
Any cell surface molecule
Cells carrying self MHC-peptide
complexes
Nature of the antigén
Natíve proteins,
carbohydrate, lipids, metals,
any structure
Processed protein fragments = peptides
Ligand
Conformational determinant
Ssequential determinant
MHC-peptide complex
Antigen recognizing receptor on
the cell surface
Variable BCR
ligand (antigen) – spcific
bivalent
Variable TCR
MHC + peptide pecific
monovalent
Soluble antigen recognizing
receptor
antibody
-
Collaboration of other cells
-
Antigen processing and presenting cells
APC – interaction of two cells
Antigen processing, presentation
-
Intracellular enzymatic degradation,
peptide or MHC transportation
Result of full activation
Production of effector
molecule antibody = soluble
BCR
Activation of new genes
Activation molecules, production of
lymphokines, TCR on the cell surface
Possibililties of cell activation
FULL
plasma cell, antibody
PARTIAL
funcional anergy
APOPTOSIS
FULL
Various lymphokines
PARTIAL
functional anergy
certain lymphokines
APOPTOSIS
CD19, CD21,
CD4, CD8, CD28/CTLA4, CD2, CD38
Co-receptors