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

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

Jelátviteli utak T-sejtekben

Fyn

Transzkripciós faktorok szerepe a T-sejt aktivációban

Antigen presentation - T cells are co-stimulated

APC Th

Signal 1 antigen & antigenreceptor

Signal 2

B7 family members (CD80 & CD86) CD28

ACTIVATION

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.

Th

ROLE OF CO-STIMULATION IN THE ACTIVATION OF HELPER T CELLS

Th

CD40

CD40L

B7B7

CD28

Th

NORMAL TISSUE CELLS DO NOT EXPRESS CD40 OR B7 CO-STIMULATORY MOLECULES

APC APC APC

Activated APC Resting APCAPC not presenting

antigen

T-cell activation T-cell anergy No effect

CD4CD4 CD28CD28CD28 CD4

B7 B7

2 1

1

2

T CELLS REQUIRE TWO SIGNALS TO GET ACTIVATED

ANTIGEN SPECIFIC ACTIVATION, ANERGY OR NEGLECTION

IL-2

IL-2R

Express a low affinity IL-2 receptor-

and chains andproduce no IL-2

Mechanism of co-stimulation in T cells

Signal 1

NFAT binds to the promoter of of the chain gene of the IL-2 receptor.

The chain converts the IL-2Rto a high affinity form

IL-2

IL-2R

1

Antigen

Resting T cells

IL-2

IL-2R

1

Antigen

2

Costimulation

Signal 2Activates AP-1 and NF-B to increase IL-2 gene transcription by 3 fold

Stabilises and thus increases the half-life of IL-2 mRNA by 20-30 fold

IL-2 production increased by 100 fold overall

Mechanism of co-stimulation in T cells

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

Gene transcriptionProliferation

IL-2

CYTOSKELETON

β γα

THE HIGH AFFINITY IL-2 RECEPTOR

Ligand bindingNo signaling

STATSignal Transducer and

Activatior of Transcription

JAKJanus kinase

~10nM ~10pM ~1nM~100pMAffinity low medium high medium

no signal no signal signal signal

α α β α β γ β γ

α βγ

α βγ γ γ γ

THE IL-2 RECEPTOR FAMILY – hematopoiesis

IL-2R IL-15RI IL-7R IL-9R IL-4RI

Loss of function mutation of the -chain results in X-linked inherited severe combined immunodeficiency (X-SCID syndrome)

adhesion

costimulation

recognition

INITIATION OF T CELL PROLIFERATION

IL-2R

G1

S

M

G0

G2

IL-1R

IL-2R

IL-2Rα

IL-2Rlow affinity

IL-2Rhigh affinity

IL-1

IL-2

transferrin

insulin PROLIFERATION

IL-2

IL-2

AUTOCRINE GROWTH FACTOR

IL-2

IL-2R

1

Antigen

Epithelialcell

NaïveT cell

Signal 1 only

Anergy

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

Self peptide epitopes presentedby a non-classical APC e.g. an

epithelial cell

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

Coreceptors deliver powerful responsesDangers 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, 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.

„Extreme responseThe 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 infection-fighting 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.

Modulation of the CD28 co-stimulatory pathway.

calcineurin

NF-ATn

NF-ATc NF-AT

Ca2+

NF-ATn

TF

calcineurinPTP-ase

calcineurinPTP-ase

calcineurinPTP-ase

P

PLC PLC

FK506CSA

Cytokines, activation molecules IL-2, IL-2R TGF

Cycliphilin A isomerase FKBP2 isomerase

Inactive phosphataseAktive phosphatase

Dephosphorylation of cytoplasmic NF-AT induces translocation to the nucleus

MECHANISM OF THE ACTION OF THE IMMUNE SUPPRESSIVE DRUG CYCLOSPORIN A AND FK506/PROGRAPH

TCR-CD3Other

receptors

NOT ANTIGEN SPECIFIC