t cell receptor (tcr) & mhc complexes-antigen presentation pin ling ( 凌 斌 ), ph.d. ext 5632;...
TRANSCRIPT
T Cell Receptor (TCR) & MHC Complexes-Antigen Presentation
• Pin Ling ( 凌 斌 ), Ph.D.
ext 5632; [email protected]
• References:
1. Abbas, A, K. et.al, Cellular and Molecular Immunology (6th ed., 2007), Chapter 5-7
2. Male D., J. Brostoff, D. B Roth, and I. Roitt Immunology (7th ed., 2006), Chapter 5 & 7
QuestionQuestion
Ans: 1. VDJ gene recombination - => V regions => Ag binding 2. Somatic hypermutation -
3. Isotype switching => Fc portion => Effector function
What are the mechanisms to generate Ab diversity?
OutlineOutline• Structures & Features of T-cell antigen Structures & Features of T-cell antigen
receptor (TCR)receptor (TCR)
• Structures & Features of Major Histocompatibility Complex (MHC)
• Antigen Presentation to T cells
• Summary & Question
Antibody, TCR & MHCAntibody, TCR & MHC
Key Concepts in T-cell Receptor (TCR)
1. T-cell antigen receptor (TCR) is similar to the F(ab) of Ab but only located on the surface of T cells => No secreted form => Two major types: TCR and TCR
2. TCR functions to recognize Ag peptide and then to activate T cells => Adaptive immunity
3. Ag recognition by TCR requires Ag presented by Major Histocompatibility Complex (MHC). => consider both Ag peptide & MHC => Cell-Cell interaction
4. The Ag-binding site region of the TCR is formed by the V and V regions.
Similarities & Differences between T-cell Receptor (TCR) and Ab
The Structure of T-cell Receptor (TCR)The Structure of T-cell Receptor (TCR)
T-cell Receptor (TCR) vs. AbT-cell Receptor (TCR) vs. Ab
Binding of a TCR to a peptide-MHC cBinding of a TCR to a peptide-MHC complexomplex
Front Side
TCR & Accessory Molecules
Accessory Molecules-Help T cells in
response to a specific Ag
1. CD3 () and
chains associates w/ TCR => intracellular signaling transduction
2. CD4/CD8: CD4 MHC-II CD8 MHC-I
3. CD28: a co-stimulatory receptor
4. Integrin: Adhesion & co-stimulation
The TCR/CD3 ComplexThe TCR/CD3 ComplexTCR/CD3 Complex:
1. TCRdimer + multiple CD3
dimers - CD3dimer - CD3 dimer
- CD3 dimer
2. The ITAM motif on CD3 => Signaling
Transduction
TCR/CD3 Complex vs BCR/IgTCR/CD3 Complex vs BCR/IgComplexComplex
Interaction between innate and& adaptive immunity
1. Innate immunity => Ag presentation (by Dendritic cells)
2. Adaptive immunity => Ag recognition (by T & B lymphocytes)
Interactions of Accessory molecules Interactions of Accessory molecules between T cells & APCsbetween T cells & APCs
OutlineOutline• Structures & Features of T-cell antigen
receptor (TCR)
• Structures & Features of Major HisStructures & Features of Major Histocompatibility Complex (MHC)tocompatibility Complex (MHC)
• Antigen presentation to T cells
• Summary & Question
Key Concepts in Major Histocompatibility Complex (MHC)
1. Ag presentation to TCR is mediated by Two classes of MHC molecules. - Class-I MHC => peptides from cytosolic (intracellular) proteins => CD8 T cells - Class-II MHC => peptides from extracellular (exogenous) proteins from phagocytosis => CD4 T cells
2. In humans, the MHC is also called as the HLA (Human Leukocyte Antigen).
3. MHC genes are the most polymorphic genes present in the genome and co-dominantly expressed in each individual.
4. MHC molecules express on the cellular surfaces of only in presence of Ag-peptides. Class-I => all nucleated cells Class-II => APCs (DC, Macrophages & B cells)
TCR-Ag w/ Histocompatibility Complex (MHC)
The Discovery of Major Histocompatibility Complex (MHC)
Histocompatibility genes: George Snell in 1940s
=> tumors or tissues => same strain, OK => foreign strains,
No
For their work leading
to the discoveries of MHC (mouse) and
HLA (human).
- Immune recognition
=> The foundation of adaptive immunity
- Transplantation
Schematic maps of human & mouse MHC loci
Class-I vs. Class-II MHC moleculeClass-I vs. Class-II MHC molecule
Structure of Class-I MHC moleculeStructure of Class-I MHC molecule
domains are polymorphic and form the peptide-binding cleft.
domain is conserved among all MHC class-I, and folds into an Ig domain for CD8 binding.
Structure of Class-II MHC moleculeStructure of Class-II MHC molecule
domains are polymorphic and form the peptide-binding cleft.
domain is conserved among all MHC class-II, and folds into an Ig domain for CD4 binding.
Polymorphic residuePolymorphic residues s of MHC moleculesof MHC molecules
In Class-I, polymorphic residues => the peptide-binding cleft formed by domains
In Class-II, polymorphic residues => the peptide-binding cleft formed by domainsIn this case HLA-DR, polymorphism is on doma
in
MHC genes are highly PolymorphiMHC genes are highly Polymorphicc
Expression of MHC alleles is co-dominantExpression of MHC alleles is co-dominant
Polymorphism & Polygeny both coPolymorphism & Polygeny both contribute to the MHC diversityntribute to the MHC diversity
Gene conversion Gene conversion creates new alleles creates new alleles in MHC genesin MHC genes
=> Copying sequences => Copying sequences from from one MHC gene to one MHC gene to
anotheranother
Gene recombination creates new Gene recombination creates new alleles in MHC genesalleles in MHC genes
MHC MHC expression expression on cells-Ion cells-I
MHC MHC expression expression on cells-IIon cells-II
Expression of MHC molecules is increased by cytokines produced during innate & adaptive immune cells, e.g. IFN
Features of Peptide-MHC interactions
1. MHC molecules show a broad spectrum for peptide binding,
in contrast to the fine specificity of Ag recognition by Ab.
2. Peptide-MHC interactions are non-covalent and mediated by
residues both in the peptides and in the clefts of MHC molecules.
3. Each MHC molecule binds one peptide at a time but can bind
many “different peptides”.
4. MHC molecules DO NOT discriminate between “Foreign Peptides” & “Self Peptides”.
OutlineOutline• Structures & Features of T-cell antigen
receptor (TCR)
• Structures & Features of Major Histocompatibility Complex (MHC)
• Antigen presentation to T cellsAntigen presentation to T cells
• Summary & Question
Key Concepts in Ag presentation between APCs & T cells
1. Most T cells recognize only peptides, whereas B cells can recognize peptides, lipids, nucleic acids,….etc. NK-T cells can recognize lipids.
2. T cells only recognize peptides displayed by MHC molecules on Ag-presenting cells (APCs).
3. APCs are responsible for capturing and displaying different Ags to T cells.
4. APCs serve two key functions for T cell activation: 1st function => process protein Ags to small peptides => form & present the peptide-MHC complex to T cells 2nd function => provide 2nd co-stimulatory signals, e.g. Cytokines & Surface Molecules
Features of Ag recognition by T cells
T cells require APCs to respond to a specific Ag
Functions of different APCs
Features of different APCs
Dendritic Dendritic cells –cells –The Most The Most effective effective APCsAPCs1. Located at common
sites of entry of microbes
2. Express receptors to capture microbes.
3. Migrate preferentially to T- cell zones in LNs.
4. Mature DCs express high levels of costimulators => T-cell activation.
Overview of Dendritic cells in Overview of Dendritic cells in Ag capture & presentationAg capture & presentation
MHC Restriction of MHC Restriction of cytotoxic T cellscytotoxic T cells
MHC Restriction-IIMHC Restriction-II
For their work leading to the
discoveries regarding the specificity of cell
mediated immunity=>MHC-restriction for T
cell recognition => Adaptive immunity
Class I vs Class II MHC pathway
The Class II MHC pathway of Ag Presentation
The Class I MHC pathway of Ag Presentation
Pathogen presentation by MHCsPathogen presentation by MHCs
Ag Presentation to different T cell subsets
SUMMARY1. TCR functions to recognize Ag peptides presented by MHC complexes => Ag peptide specificity => MHC restriction
2. Two classes of MHC molecules. - Class-I MHC => peptides from cytosolic (intracellular) proteins => CD8 T cells - Class-II MHC => peptides from extracellular (exogenous) proteins from phagocytosis => CD4 T cells
3. APCs serve two key functions for T cell activation: 1st function => process & present Ag peptides w/MHC to
T cells 2nd function => provide 2nd co-stimulatory signals, ex. cytokines & surface molecules
QuestionsQuestions
What is the Bare LymphocyteSyndrome?
What is the advantage of MHC Polymorphism? Is that good if MHC is as diverse as Ig or TCR?