Transcript 7-8 lectureTCR_L

A T-cell precursors migrate from the
bone marrow to thymus
Shaping the T-cell repertoire.
Positive and negative selection Thymus
Few TCR reacts with
the MHC (about 2%) most
T-cells die of neglect.
( no survival signals)
α-chain rearrangement can
continue until the assembly of
a functional αβ receptor
has been assembled.
Selection of developing T-cells in the thymus
Bare lymphocyte syndrome
MHCI vagy MHCII deficiency
Lack of CD8+ or CD4+ cells
Role of co-receptors in the
development of single +
T-cells
DC Macrophage in medulla of
Thymus. Special transcription
factor expressed… AIRE.
Tissue spec. Antigens expressed
AIRE mutaton: Autoimmune
polyendocrinopathy
-candidiasis-ectodermal
dystrophy
Multiple stages of T-cell development in the thymus
Dendritic cells take up antigen in the tissues, migrate to peripheral lymphoid
organs, and present foreign antigens to naive T cells.
Changes in the function of dendritic cells following
Activation, migration to the regional lymph node, maturation
Uptake of antigen, maturation
Differentiation/maturation
Antigen prezentation
Red: lizozyme green: MHCII
A naive cells meet dendritikuc cells in the secondary
lymphoid organs
(review)
Phases of T cell response
The site of interaction between T cell and APC is called
The imunological synapse
Clustering of the T-cell receptor and a co-receptor
initiates signaling within the T cell.
(review)
TCR signaling
T CELL ACTIVATION
CHARACTERISTICS OF T-CELL ANTIGEN RECOGNITION
1. The TCR is not able to interact directly with soluble or cell-bound antigen
2. T-cell activation can be induced by antigen in the presence of acessory
cells, only
3. T-cells recognize virus-infected cells
ACCESSORY CELL
ANTIGEN BINDING
NO INTERACTION
V
T-CELL
ACTIVATION
C
Antigen receptor
B-CELL
a/b
T-CELL
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
(review)
Phases of T cell response
(review)
BCR signaling
(review)
TCR signaling
Intracellular (cytoplasmatic) Ca2+ concentration increase
The intracytoplasmatic Ca2+ increase can be monitored by
fluorescent indicator dye. The intensity or the specificity of
fluorescence increase paralelly with the Ca2+ concentration.
Kinetic measurements connected to
signaling (1.)
Homogenous population – single cell property
measured one after the other - timing
Detected in
Detected in single cell
homogenous
population –
measured cell by
cell
Indicator – detection of intracellular Ca2+ signal
fluorescent Ca2+ indicators Fluo-3 or Indo-1
Kinetic measurements connected to
signaling (2.)
Fluo-3 AM – excitable by blue light
Indo-1 AM – excitable by UV light
These indicator dyes connected with apolar groups (e.g. acetoxy-methylester:
AM) – go across the cell membrane. In the cell, estherases cleveage these
groups - the fluorochrome became polar – catched in the cell
for example – ic Ca2+ signal in a single cell
antigen presentation by B cell to T cell
(click)
THE IMMUNOLOGICAL SYNAPSE
APC
T
APC
T CELL
THE INTERACTION OF T CELLS AND ANTIGEN
PRESENTING CELLS
interaction
recognition
1
2
3
4
5
6
stabilization
7
8
separation
Negulescu P.A. et. al. Immunity 4: 421-430, 1996
T-cells need two signals!!!! The role of
co-stimulation
Antigen presentation - T cells are co-stimulated
Signal 1 antigen & antigen
receptor
T
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
Mechanism of co-stimulation in T cells
Antigen
1
IL-2
IL-2
IL-2Ra
IL-2Ra
Resting T cells
Express a low affinity
IL-2 receptorb and  chains and
produce no IL-2
Signal 1
NFAT binds to the promoter of of the
a chain gene of the IL-2 receptor.
The a 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-2Ra
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
INITIATION OF T CELL PROLIFERATION
IL-2R
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 GROTH
FACTOR
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
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
Anergy
Antigen
Naïve
T cell
1
Signal 1 only
IL-2
IL-2Ra
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
Dendritic cells are sensors, gatekeepers and messengers
Activation induces a phenotype essential for
the initiation of the adaptive immune response
ACTIVATION AND MIGRATION OF DENDRITIC CELLS
TISSUE
LYMPH NODE
LYMPH
Activated DC
TISSUE
Effector and memory T
cells
Inflammation
Pathogen
Naive T cells
ANTIGEN
Tissue DC
INTERACTION OG
DC AND T CELL
T CELL
ACTIVATION
BLOOD
DENDRITIC CELL T LYMPHOCITE
INTERACTION IN THE
LYMPHOID ORGANS
Activated dendritic cells in the
lymphatic tissues act as antigen
presenting cells
Tight contact with specific T cells
DENDRITIC CELL-T CELL INTERACTIONS IN THE T-CELL
AREAS OF LYMPH NODES
NUCLEUS
T CELL
T CELL
CYTOPLASM
Cell-surface molecules of the immunoglobulin superfamily
initiate lymphocyte adhesion to professional
antigen-presenting cells
B. Transient interactions are stabilized by Ag-binding
A.
A
Initial contact
Rapid DC Migration in the Subcapsular
Space
Bone-marrow derived DCs (green)or (50
µM Cell Tracker Blue, blue) were injected
into the footpad of a C57BL/6 mouse,
followed 18 hours later by intravenous
injection of freshly isolated T cells ( red)
Capture of an Ag-Specific T Cell by an
Ag-Bearing DC
Bone-marrow derived DCs (yellow) were
pulsed with 1 µM Ova 4 peptide and 10 µM
Ova for 1 hour at 37oC, then injected into the
footpad of a C57BL/6 recipient. This was
followed 6 hours later by i.v. co-injection of
CD8+ T cells (green) and CD4+ T cells (red).
Huang et al Immunity 2004
The stages of activation of CD4 T cells.
Different cytokine environments drive the differentiation
of CD4 T cells that make different cytokines and have
different functions.
Responses to Mycobacterium leprae are sharply
differentiated in tuberculoid and lepromatous leprosy.
Granulomas develop when intracellular
pathogens resist elimination
Long term persistance of infectious
agent in a separated envitonment
The three types of effector T cell produce distinct
sets of effector molecules.
TH1 CD4 cells activate macrophages
to become highly microbicidal.
TH2 cells stimulate the proliferation and
differentiation of naive B cells.