ANTIGEN PRESENTATION

T – CELL RECOGNITION

T – CELL ACTIVATION

T – CELL EFFECTOR FUNCTIONS

Lymphocyte subsets

Activate B cellsand macrophagesT HELPER CELLS

Th

Kill virus-infected cells

CYTOTOXIC TLYMPHOCYTES

CTL

Produce antibodiesPLASMA CELLS

PC

T B

T CELLS B CELLS

CLP

Commonlymphoidprecursor

RECOGNITION EFFECTOR CELL

Macrophage activation

Lymphocyte activation

Inflammation

Plasma cell

Antibody production

cytokines

B-lymphocyte

cytokinesBCR + antigen

Cytotoxic T-limfocyte (Tc)

TCR + peptide + MHC-I

Helper T-lymphocyte (Th)

TCR + peptide + MHC-II

Cell killing

Effector cell retains specific receptor

Effector cells secrete cytokines

Peptides of endogenous proteins (virus, tumor) bind to class I MHC

molecules

Tc

Endogenous Ag

RECOGNITION OF EXOGENOUS AND ENDOGENOUS ANTIGENES BY T-LYMPHOCYTES

Exogenous Ag

Th

Peptides of exogenous proteins (toxin, bacteria, allergen) bind to class II MHC

molecules

How can 6 invariant molecules have the capacity tobind to 1,000,000,000,000,000 different peptides?

The number of different T cell antigen receptors is estimated to be

1,000,000,000,000,000 (1015 - 17)

A flexible binding site?

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 receptorwith the T cell antigen receptor• prevent exchange of the peptide with others in the extracellular milieu

A binding site that is flexible enough to bind any peptide?

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.

Floppy CompactAllows 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

Venus fly trap

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?

Golgi

ER

citoplazma

THE ENDOGENOUS ANTIGEN PROCESSING PATHWAY

Tc-cell

ProteasomeLMP2/LMP7

PROTEIN

SELF

ANTIGEN

TAP1/2gp96 calnexin

α-chain

α-chain+β2m MHC+peptide

MHC-I + Ag peptide

MHC-I +self peptide

CLOSEDFLEXIBLEcytoplasm

MHC-I, LMP2/7, TAP

IFN induced coordinated expression

ER membrane

Lumen of ER

Cytosol

Transporters associated withantigen processing (TAP1 & 2)

Transporter has preference for longer than 8 amino acid peptideswith hydrophobic C termini.

TAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

Peptide

ER membrane

Lumen of ER

Cytosol

TAP-1 TAP-2

Peptide

ATP-binding cassette(ABC) domain

Hydrophobictransmembranedomain

Peptide antigensfrom proteasome

Endoplasmic reticulum

Calnexin bindsto nascent

class I chainuntil 2-M binds

TAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

TAP-1 TAP-2

PeptideTAP-1 TAP-2

Peptide

B2-M binds and stabilises

floppy floppy MHCMHC

Tapasin, calreticulin, TAP 1 & 2 form a complex with

the floppy MHCfloppy MHC

Cytoplasmic peptides are loaded onto the

MHC molecule and the structure becomes

compact

Maturation and loading of MHC class I

Golgi

ER

CLIP

MCII

CIIV

DMA/B

li

M H C IIli

Th-cell

INVARIANT CHAIN (Ii)

1. Chaperone – conformation

2. Inhibition of peptide binding

3. Transport/retention

CLOSEDFLEXIBLEIi+αβ

CLIP

DMA/B

DMA/DMB

1. Support the peptide receptive conformation

2. Exchange of CLIP for exogenous peptides

MHC-II + Ag peptide

MHC-II +self peptide

THE EXOGENOUS ANTIGEN PROCESSING PATHWAY

GENERATION OF MHC – II EPITOPESGENERATION OF MHC – I EPITOPES

Viral protein

B27

A2

B35

C42

HLA-A,B,C binding

The Tc response is focused to few epitopes

ENSURE RECOGNITION OF ANY PATHOGENIC PROTEIN

The Th response is directed to overlapping epitopes

ENSURE RECOGNITION OF ALL PROTEINS

HLA-DR1/HLA-DR4

Overlapping peptides

HLA-DQ2/HLA-DQ7

TARGETS OF EPSTEIN-BARR VIRUS-SPECIFIC TARGETS OF EPSTEIN-BARR VIRUS-SPECIFIC Tc (CTL) RESPONSESTc (CTL) RESPONSES

• A poliklonális CTL válasz elsősorban a litikus antigének és azA poliklonális CTL válasz elsősorban a litikus antigének és az EBNA3,4,6 nukleáris fehérjék ellen irányulEBNA3,4,6 nukleáris fehérjék ellen irányul• Erősen fókuszált egy adott MHC - peptid kombinációraErősen fókuszált egy adott MHC - peptid kombinációra• Az endogén EBNA1 nem processzálódik és így nem ismerhető felAz endogén EBNA1 nem processzálódik és így nem ismerhető fel

EBNA3EBNA3EBNA5EBNA5 EBNA2EBNA2

WWWW WWWW WWWW WWWW WWWW WWWWZZZZWWWW WWWW WWWW WWWW WWWWCCCC YYYYHHHH FFFF QQQQUUUUPPPPOOOO MMMM SSSS LLLL EEEE RRRR KKKK BBBB DDDD TTTTXXXXVVVV IIII AAAAGGGG NNNNhhhheeeettttNNNNhhhheeeetttt

EBNA6EBNA6EBNA1EBNA1LMP2LMP2

EBNA4EBNA4LMP1LMP1

--

BZLF1BZLF1BMLF1BMLF1BMRF1BMRF1

BHRF1BHRF1 BARF0BARF0

++ ± ± (?)(?) ±±++++ ++++ ++++

++

++++++++ ++++ ++++

LYTIC ANTIGENS

LATENT ANTIGENS

MHC class I MHC class II

Bound peptide 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

Generation of peptide

site cytoplasm vesicles, endo/lysosomes

enzyme proteasomeLMP-2, LMP-7 regulatory subunits

vesicular acidic proteases cathepsins

transport TAP - size and C-terminal dependentcytoplasm ER

no

MHC transport no Ii - target, retentionER vesicular systemspecial compartment

MHC - peptide interaction

site ER vesicles, CIIV

chaperons calnexin, toposin Ii - CLIP, DMA/B

MHC - peptide complexes In the cell surface

stable complexes reflecting the endogenous environment of the cellfew instable empty molecules

stable complexes reflecting the exogenous/endogenous environment of the cellfew re-circulating molecules complexed with CLIP

JAK1 JAK1

P– P–

STAT-dimer STAT-dimer

IRF-1IRF-1 CIITA

Co-aktivátorp58

ISREA B CAATCCAAT

TATATATA

MHCIIMHCI

JAK2 JAK2

IFNg

IFNRgTNF

TNFRI

TRAFI Bk

NFBk

IKKp65p55 p65p55

TRADD

a ab b

YP–Y–P YP–

Y–P

YP–Y–P

YP–Y–P

YP–Y–P

YP–Y–P

Y YP P

X2bpRFXW/S

X1 X2 Y

NF-Y

REGULATION OF MHC CLASS I AND II SYNTHESIS

REGULATION OF CLASS I AND II MHC MOLECULES

IFNγ

IFNγR

Type II immune IFNγ increases MHC expressionInflammatory 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, particlesAny 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 determinantSsequential determinant

MHC-peptide complex

Antigen recognizing receptor on the cell surface

Variable BCRligand (antigen) – spcificbivalent

Variable TCR MHC + peptide pecificmonovalent

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 genesActivation molecules, production of lymphokines, TCR on the cell surface

Possibililties of cell activation FULLplasma cell, antibody PARTIALfuncional anergy

APOPTOSIS

FULLVarious lymphokines PARTIAL functional anergycertain lymphokinesAPOPTOSIS

Co-receptors CD19, CD21, CD4, CD8, CD28/CTLA4, CD2, CD38