How T cells recognize antigen: Identifying the TCR: The T...
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1 How T cells recognize antigen: The T Cell Receptor (TCR) Lecture 11, MCB 150 Laurent Coscoy 2 Identifying the TCR: Why was it so hard to do? •By the early 1980s, much about T cell function was known, but the receptor genes had not been identified •Recall that Ig was purified as soluble myeloma protein •There is no soluble form of T Cell Receptor 3 Monoclonal antibody approach (Allison and colleagues 1982) Probed with cDNA clone 1 Probed with cDNA clone 2 T cell clones Liver cells B cell lymphoma Hedrick & Davis strategy: Subtractive cDNA cloning
Transcript of How T cells recognize antigen: Identifying the TCR: The T...
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How T cells recognize antigen:The T Cell Receptor (TCR)
Lecture 11, MCB 150Laurent Coscoy
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Identifying the TCR:Why was it so hard to do?
•By the early 1980s, much about T cell functionwas known, but the receptor genes had not beenidentified
•Recall that Ig was purified as soluble myelomaprotein
•There is no soluble form of T Cell Receptor
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Monoclonal antibody approach
(Allison and colleagues 1982)4
Probed with cDNA clone 1
Probed with cDNA clone 2
T cell clones
Live
r cel
lsB
cell
lym
phom
a
Hedrick & Davis strategy: Subtractive cDNA cloning
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TCR: Anαβ
heterodimer
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A second type of TCR
• Hetero dimer of γ and δ chains (like α and βchains)
• Expressed on a rare subset of T cells withfascinating properties (more later)
αβ T cells γδ T cells
CD4 T cells CD8 T cells
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Comparison of TCR and BCR (Ig)
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T cell receptor lociAnalogous to B cell receptor loci
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Generation of the T cell receptor
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TCR structure
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TCR:Peptide/MHC I
Interaction
Constant domains
Variable domains
CDR3’s
Peptide
Binding groove
C C
V
V
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Class I Class II
Peptide Binding Grooves of MHC Molecules
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Soluble peptide/MHC complexes: aprobe to detect specific T cells
Ig HC Fc Region
MHC I
Made by geneticengineering; doesnot exist in nature
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HTLV-I and tropical spastic paraparesis
HTLV-I:- human retrovirus, persistent infection- 20 millions people are infected worldwide- encodes the oncogene Tax
TSP:- progressive inflamatory disease of the CNS- pathogenesis not fully understood
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FollowingAntigen-Specific T
Cells
CD8 16
CD4 and CD8:Co-receptors for
the TCR
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What’s with these “CD” names?
• “CD” stands for cluster of differentiation
• Many labs generated monoclonal antibodies against cell-surface proteins --> naming of antibodies and their targetswas a mess
• Conference was called to “clean up” the naming business
• Target of monoclonal ab directed against the same surfaceprotein or complex was given a number, as in CD3, CD4,etc.
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Co-receptors bind to non-polymorphicregions of MHC I (CD8) or II (CD4)
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CD4 and CD8 mark mutuallyexclusive subsets of mature T cells
Anti-CD8
Ant
i-CD
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Anti-CD3
Ant
i-B22
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Flow cytometry of spleen
Anti- TCR
Ant
i-CD
4 &
Ant
i-CD
8
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Contrast how B and T cells see antigen
B Cell
T Cell APC
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TCR affinity is quite low
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Mysteries in T cell antigen recognition
• About 105 copies of each MHC molecule oncell surface
• Frequency of any particular Peptide:MHCcomplex may be as low as 0.01%
• How does the TCR sort through all thoseincorrect complexes and find ones withwhich to trigger?�
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Co-receptor and adhesionmolecules improve avidity
CD2 LFA-3
LFA-1 ICAM-1
TCR
CD4 or CD8
MHCT cell target cell
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Immunological Synapse: A model
T cell T cellT cell
APC APC APC
Red: adhesionGreen: Antigen
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Immunological “synapse”
Peptide-MHC complexes
Adhesion molecules (ICAM-1)
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The synapse in real-time
T-Cell
B-Cell(Peptide-pulsed )
8 minutes in 20 seconds of video
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The synapse in real-time
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TCR Signal Transduction
Why do we care?
It helps us understand T cell function
It gives us molecular targets for immunotherapy
It is an amazing example of biological complexity
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Consequences of T cell activation
How is TCR:peptide:MHC binding linked to these events?
ProliferationCell cycle entry and cell divisionClonal expansion
DifferentiationSecretion of cytokines (helper cells)Activation of killer functions (cytotoxic cells)Acquisition of effector functionMemory
DeathImportant for down-regulation of immune response
TCR signaling induces changes in gene expression
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Example of T cell activation
TCR binds peptide:MHC
Induces expression of genes
T cells divides many times creatingmore T cells with the same TCR
T cells differentiate andacquire new characteristics
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Signal Transduction
Transmission of external signals across themembrane and conversion of these signals intointracellular biochemical events
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TCR
Peptide:MHC
Changes in gene expression
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RECEPTOR
?
? ?
?? ?
Alterations inGene expression
TCR signaling: Big Picture
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How does the TCR transduce signals with such a little tail?
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TCR associates with the CD3 Complex
Analogous to the Igαand Igβ proteins thatassociate with BCR onB cells
