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T CELL RECEPTOR MEDIATED SIGNALING
Multisubunit Immune
Recognition Receptors
APC
MIRR
MHC
Antigen
Antigen
TCR
BCR
αβ
s
V s
s
sV
s
C s
s
sC
ss
P
P
D/E X7 D/E X2 YXXL/I X7 YXXL/I
ITAM
Immunoreceptor Tyrosine-based
Activation Motif
ACTIVATION
CD3
CD3
εδ
s s
s s
εγ
s s
s s
ζζ
s s
INTERACTION OF THE TCR WITH MHC-PEPTIDE
COMPLEXES IS ESSENTIAL BUT NOT SUFFICIENT
FOR T-CELL PRIMING
INVOLVEMENT OF ADHESION AND COSTIMULATORY MOLECULES
CONVERGING SIGNALING PATHWAYS IN T CELL
ACTIVATION
CD4/CD8 costimulation
CD28 costimulation
THE ADHESION AND CO-STIMULATORY MOLECULES CD4 AND CD8
APC
MARKERS OF T CELL
SUBPOPULATIONS
MHCII
+
peptid
ADHESION MOLECULE
TCR
CD4
APC
MHCI
+
peptid
TCR
BINDS TO MHC
p56lck
p56lck
SIGNALING MOLECULE
+
CD4 T-sejt
CD8
CD8+ T-sejt
TARGET CELL
PROFESSIONAL APC
CD8
1
s
s
2
V4
2
s
s
s
s
α β
Lck
Helper T-cell
SIGNAL
Lck
a b T-cell
Cytotoxic
1
V3
2m
s
s
3
V2
CD4
s
s
3
s
s
2m
V1
2
1
2
1
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
TCR signaling
Fyn
Role of transcription factors in T-sejt activation
Antigen presentation - T cells are co-stimulated
Signal 1 antigen & antigen
receptor
Th
APC
ACTIVATION
Signal 2
B7 family members (CD80 & CD86)
CD28
Costimulatory molecules are expressed by professional APC including dendritic cells,
monocytes, macrophages, and B cells, but not by cells that have no
immunoregulatory functions such as muscle, nerves, hepatocytes, epithelial cells etc.
ROLE OF CO-STIMULATION IN THE ACTIVATION OF
HELPER T CELLS
Th
Th
Th
CD40L
CD28
CD40
B7
B7
APC
APC
APC
NORMAL TISSUE CELLS DO NOT EXPRESS CD40 OR B7 CO-STIMULATORY
MOLECULES
T CELLS REQUIRE TWO SIGNALS TO GET ACTIVATED
Activated APC
Resting APC
B7
CD28
APC not presenting
antigen
B7
CD4
2 1
T-cell activation
CD4
CD28
1
T-cell anergy
CD4
CD28
2
No effect
ANTIGEN SPECIFIC ACTIVATION, ANERGY OR NEGLECTION
CO-STIMULATION IS ESSENTIAL FOR PRIMING OF
NAIVE T LYMPHOCYTES
The antigen-specific and the co-stimulatory signals have to be
induced in concert to induce T lymphocyte activation
The antigen-specific and co-stimulatory signals can be
delivered simultaneously by professional antigen presenting
cells, only
The antigen-specific and the co-stimulatory singnals has to be
delivered by the same professional antigen presenting cell
Mechanism of co-stimulation in T cells
Antigen
1
IL-2
IL-2
IL-2R
IL-2R
Resting T cells
Express a low affinity
IL-2 receptor and  chains and
produce no IL-2
Signal 1
NFAT binds to the promoter of of the
 chain gene of the IL-2 receptor.
The  chain converts the IL-2R
to a high affinity form
Mechanism of co-stimulation in T cells
Costimulation
Antigen
Signal 2
1
2
Activates AP-1 and NFk-B to increase IL2 gene transcription by 3 fold
Stabilises and thus increases the half-life
of IL-2 mRNA by 20-30 fold
IL-2
IL-2R
IL-2 production increased by 100 fold
overall
Immunosuppressive drugs illustrate the importance of IL-2 in immune responses
Cyclosporin & FK506 inhibit IL-2 by disrupting TcR signalling
Rapamycin inhibits IL-2R signalling
THE HIGH AFFINITY IL-2 RECEPTOR
IL-2
Ligand binding
No signaling
α
β
γ
JAK
Janus kinase
CYTOSKELETON
Gene transcription
Proliferation
STAT
Signal Transducer and
Activatior of Transcription
THE IL-2 RECEPTOR FAMILY – hematopoiesis
α
α β
α β γ
~ 10nM
~ 100pM
~ 10pM
medium
high
medium
no signal
signal
signal
Affinity
low
no signal
α β
γ
IL-2R
α β
γ
IL-15RI
β γ
~ 1nM
γ
γ
γ
IL-7R
IL-9R
IL-4RI
Loss of function mutation of the -chain results in X-linked inherited severe
combined immunodeficiency (X-SCID syndrome)
INITIATION OF T CELL PROLIFERATION
IL-2R
adhesion
IL-2
recognition
IL-2Rα
costimulation
IL-1R
IL-1
IL-2R
G0
IL-2R
low affinity
G1
IL-2
M
G2
IL-2R
high affinity
S
transferrin
IL-2
insulin
PROLIFERATION
AUTOCRINE GROWTH
FACTOR
Anergy
Antigen
Naïve
T cell
1
Signal 1 only
IL-2
IL-2R
Epithelial
cell
Self peptide epitopes presented
by a non-classical APC e.g. an
epithelial cell
The T cell is unable to produce IL-2 and
therefore is unable to proliferate or be clonally
selected.
Unlike immunosupressive drugs that inhibit ALL
specificities of T cell, Signal 1 in the absence of
signal 2 causes T cell unresponsiveness to a
specific antigen
Coreceptors deliver powerful responses
Dangers of triggering strong co-stimulatory signals
Mice are not humans
Cytokine storm in a phase 1 trial of the anti-CD28 monoclonal antibody
TGN1412.
Suntharalingam G,
Panoskaltsis N.
N Engl J Med. 2006 Sep 7;355(10):1018-28.
Six healthy young male volunteers at a contract research organization were enrolled
in the first phase 1 clinical trial of TGN1412, a novel superagonist anti-CD28
monoclonal antibody that directly stimulates T cells. Within 90 minutes after receiving
a single intravenous dose of the drug, all six volunteers had a systemic inflammatory
response characterized by a rapid induction of proinflammatory cytokines and
accompanied by headache, myalgias, (pain in multiple muscles) nausea, diarrhea,
erythema, vasodilatation, and hypotension. Within 12 to 16 hours after infusion, they
became critically ill, with pulmonary infiltrates and lung injury, renal failure, and
disseminated intravascular coagulation. Severe and unexpected depletion of
lymphocytes and monocytes occurred within 24 hours after infusion. All six patients
were transferred to the care of the authors at an intensive care unit at a public
hospital, where they received intensive cardiopulmonary support (including dialysis),
high-dose methylprednisolone, and an anti-interleukin-2 receptor antagonist antibody.
Prolonged cardiovascular shock and acute respiratory distress syndrome developed
in two patients, who required intensive organ support for 8 and 16 days. Despite
evidence of the multiple cytokine-release syndrome, all six patients survived.
Documentation of the clinical course occurring over the 30 days after infusion offers
insight into the systemic inflammatory response syndrome in the absence of
contaminating pathogens, endotoxin, or underlying disease.
Modulation of the CD28 co-stimulatory pathway.
„Extreme response
The drug, an antibody called TGN1412, is being developed by German
company TeGenero with the aim of directing the immune system to fight cancer
cells, or calm joints inflamed by rheumatoid arthritis. The antibody binds to a
receptor molecule called CD28 on the surface of the immune system's infectionfighting T cells. (Nature March 17 2006)
Scientists who work in the field say there are several possible ways that the
drug could have triggered multiple organ failure. It may have stimulated T cells
so much that they released an overwhelming flood of inflammatory molecules
called cytokines. Or perhaps wayward T cells launched an attack on the body's
own tissues, ignoring the safety mechanisms that normally keep this in check.
APC
MHC+antigén
Signal strength, ratio
and duration of various
signals
B7
CD4
T-sejt
receptor
CD28
CD45
  
-P
DAG
PKC
Lck
Fyn
Ca2+
LAT
PLC PI3K
ZAP-70
Csk
PtdIns4,5P2
IkB
Ca2+
PtdIns3,4,5P3
Ca2+
CN
PKC
Vav
Rho/Rac
IP3
Ca2+ 2+
Ca
Ca2+ 2
Ca +
Ca2+
Ras
LAT
Sos
Sos
Grb2
SLP76
Cbl
NF-kB
Raf
P
MAPK
P
IkB
CN
NFAT
P P
NF-kB
NFAT
transzkripciós faktorok foszforilációja
korai génexpresszió
NFAT
AP-1
NF-kB
OCT
Activation of new
genes
How much and which
INTRACELLULAR EVENTS OF T CELL ACTIVATION
SIGNAL TRANSDUCTION
APC
MHC+antigén
Enzimatic modification
(kinases, phosphatases,
proteases)
CD4
T-sejt
receptor
CD28
CD45
Local concentration
(recruitment or
sequestration of
interacting
components
PKC
Lck
Fyn
Ca2+
LAT
PLC PI3K
ZAP-70
Csk
Ras
LAT
Grb2 Sos Sos
SLP76
Cbl
PtdIns4,5P2
IkB
Ca2+
PtdIns3,4,5P3
Ca2+
CN
P
MAPK
NF-kB
NFAT
transzkripciós faktorok foszforilációja
korai génexpresszió
NFAT
AP-1
NF-kB
NF-kB
Raf
CN
NFAT
P P
PKC
Vav
Rho/Rac
IP3
Ca2+ 2+
Ca
Ca2+ 2
Ca +
Ca2+
Timing
(pathway can go to diverse
directions,
first one will be realized)
Allosteric effects
(binding activates or
inactivates)
  
-P
DAG
OCT
NEW GENES
P
IkB
MECHANISM OF THE ACTION OF THE IMMUNE SUPPRESSIVE DRUG
CYCLOSPORIN A AND FK506/PROGRAPH
TCR-CD3
Other
receptors
PLC
Inactive phosphatase calcineurin
PLC
Ca2+
calcineurin
PTP-ase
NF-ATc
P
NF-AT
calcineurin
PTP-ase
CSA
FKBP2 isomerase
NF-ATn
TF
NOT ANTIGEN SPECIFIC
calcineurin
PTP-ase
Dephosphorylation of
cytoplasmic NF-AT induces
translocation to the nucleus
FK506
Cycliphilin A isomerase
NF-ATn
Active phosphatase
Cytokines, activation molecules
IL-2, IL-2R
TGF