Antigen presentation in a nutshell
ANTIGEN-SPECIFIC T – CELL ACTIVATION
PARTNERS
Antigen presenting cell carrying antigenic peptides bound to MHC – pre-formed MHC – peptide complexes – INDEPENDENT OF T CELLS
Self MHC with captured antigenic peptide interacts with antigen-specific T lymphocytes selected from
the available T cell repertoire
INTERACTION
MHC – peptide complex (ligand)
T cell receptor
T-sejt
TCR
APC
MHC
T-sejt T-sejt
TCR TCR
APC
MHC
APC
MHC
MHC RESTRICTION
One single T-cell receptor can recognize a given MHC – peptid complex
The TCR-specific peptide is recognized only when its presented with an MHC on which the TCR had been selected during its development in the thymus
If the peptide binds to another MHC molecule no T-cell recognition occurs
If the same MHC molecule binds another peptide, no T-cell recognition occurs
MMOUSEOUSE YY
Virus AVirus A T -T - CELLS CELLS
TT
TTTT
TTTT TT
Virus BVirus B+ + YY cellscells
TT
Virus AVirus A+ + YY cellscells
TT
MMOUSEOUSE X X
Virus AVirus A+ + X X cellscells
TT
Virus AVirus A+ + X X cellscells
TT
TT
THE EXPERIMENT OF DOHERTY & ZINKERNAGEL 1976
The virus infected cell must derive from the same strain as the T cell
They have to be MHC identical
Specific for self and virus
Normal cell Infected cell
T
RECOGNITION OF CORRECT MHC – PEPTIDE COMPLEXES BY THE SPECIFIC T-CELL
APC AND T CELL INTERACTION
IS IT SUFFICIENT FOR T CELL ACTIVATION?
WHERE AND WHEN CAN OCCUR?
HOW IS IT INDUCED?
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CDR1 CDR2 CDR3
-chain
-chain
CDR1 CDR2 CDR3
V C
-CHAIN
Diszulfid hidak
CDR1 and CDR2 are not hypervariable
NO SOMATIC HYPERMUTATION
Variability of CDR3 is the result of joining variability
NH2
COOH
VARIABILITY AND ORIENTATION OF CDR IN THE T CELL RECEPTOR
N
N
C
CMHC
MHC
N
N
C
CMHC
MHC
N
N
C
CMHC
MHC
1
2
3 1
2
3
INTERACTION OF THE T - CELL ANTIGEN RECEPTOR WITH AN MHC – PEPTIDE COMPLEX
1. The TCR is monovalent, binds a single MHC – peptide complex
2. The affinity of the TCR – peptide – MHC interaction is low 10-5 - 10-6 M/l
3. A defined MHC – antigenic peptide complex is displayed in the cell membrane together with various other MHC – peptide complexes (DILUTED LIGAND) most complexes are MHC/peptide complexes
4. How many MHC – peptide complexes are needed for T cell signaling?
TCR - MHC1
TCR - MHC1
CDR3 - peptide
APC T
THE IMMUNOLOGICAL SYNAPSE
25.6_immuno_synapse.mov
THE IMMUNOLOGICAL SYNAPSE
T CELL
ANTIGEN PRESENTING CELL
CD48
CD2
ICAM-1
LFA-1
B7
CD28CD4
SIGNALING COMPLEX
adaptor
ACTIVATEDT CELL
ICAM – Intercellular Adhesion Molecule
Antigen
BCR
Antigen
MHC
TCR
CD3
APC
s s
ss
ss
s
ss
V V
C C
s
α βss
ss
ss
ss
CD3
s s
ε δ ε γζ ζ
D/E X7 D/E X2 X7 YXXL/I YXXL/IP P
ITAMImmunoreceptor Tyrosine-based
Activation Motif
ACTIVATION
T CELL RECEPTOR MEDIATED SIGNALING
Multisubunit Immune Recognition Receptors
MIRR
7-1_TCR_Signaling.mov
TCR signalling
Fyn
APC
T cell
interaction recognition
1 2 3 4
5 6 7 8
stabilization separation
Negulescu P.A. et. al. Immunity 4: 421-430, 1996
THE INTERACTION OF T CELLS AND ANTIGEN PRESENTING CELLS
Role of transcription factors in T-sejt activation
TCR signaling
?
C D 4 5 R O
C D 5
C D 4
C D 3
C D 2
C D 2 8
C D 1 5 2 ( C T L A - 4 )
C D 4 9 d / 2 9 ( V L A - 4 )
C D 1 5 4 ( C D 4 0 L )
C D 4 0
C D 2 2
C D 7 2
M H C I I
C D 5 8 ( L F A - 3 )
C D 5 9
C D 8 0 ( B 7 - 1 )
C D 8 6 ( B 7 - 2 )
C D 2 0
C D 4 3
C D 1 0 6 ( V C A M )
C D 5 4 ( I C A M - 1 )C D 1 1 a / 1 8 ( L F A - 1 )
C D 1 0 2 ( I C A M - 2 )
C D 5 0 ( I C A M - 3 )
C D 1 9
C d 7 9bC d 7 9a
s I g M
C D 2 1 ( C R 2 )
C D 8 1 ( T A P A )
C D 2 3 ( F c R I I )e
M H C I
C D 8
BCR
TCR
THE CONTACT OF APC AND T CELLS IS STABILIZED BY ADHESION MOLECULES
*
*
*
*
*
B CELL T CELL
MHCI – CD8
MHCII – CD4
CD40 – CD40L
B7 – CD28
KINETICS OF LYMPHOCYTE ACTIVATION
ANTIGEN SIGNAL1.
co-receptorAdhesion molecule
Cytokines SIGNAL2.
Resting lymphocyte G0PTK activation RNA synthesis Free Ca++ Protein synthesis Protein phosphorylation DNA synthesis
Lymphoblast
0 10sec 1min 5min 1hr 6 hrs 12 hrs 24 hrs
Nyugvó limfocita G0
G1
G2
M
Ssejtosztódás
DNA synthesis
Effector cell Memory cell
Transport Membrane changeRNA and protein synthesis
Resting lymphocyte G0
CONVERGING SIGNALING PATHWAYS IN T CELL ACTIVATION
CD4/CD8 costimulationCD28 costimulation
INTERACTION OF THE TCR WITH MHC-PEPTIDE COMPLEXES IS ESSENTIAL BUT NOT SUFFICIENT
FOR T-CELL PRIMING
INVOLVEMENT OF ADHESION AND CO-STIMULATORY MOLECULES
Lck
ss
ss
ss
ssV4
V1
V2
V3
Helper T-cell
CD4
CD4 T-sejt+
MHCII+
peptid
TCR CD4
APC
p56lck
CD8TCR
MHCI+
peptid
APC
CD8 T-sejt+
p56lck
THE ADHESION AND CO-STIMULATORY MOLECULES CD4 AND CD8
SIGNAL
2
1
2
1
PROFESSIONAL APC
CD8
b
ss
a
ss
LckCytotoxic T-cell
α β
TARGET CELL
1
3
2
2m
1
3
2
2m
MARKERS OF T CELL SUBPOPULATIONS
ADHESION MOLECULE
BINDS TO MHC
SIGNALING MOLECULE
THE RATIO OF CD4+/CD8+ T CELLS IS STABLE IN HEALTHY INDIVIDUALS
CD4+ : CD8+ = 1.6
Normal CD4+ T-cell counts = 600 – 1400/ l
HIV infection AIDS = CD4+ T cell count <200/l
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