chapter 11 antigen presenting cells and antigen presenting
DESCRIPTION
Chapter 11 Antigen Presenting Cells and Antigen Presenting. B. B. B. B. B. B. B. B. B. Y. Y. Y. Y. Y. Y. Y. Y. Y. Y. T. T. Y. Y. T cells do not recognise native antigens. Y. Y. Y. Y. Y. Y. Cross-linking of surface membrane Ig. - PowerPoint PPT PresentationTRANSCRIPT
Chapter 11
Antigen Presenting Cells and
Antigen Presenting
T cells do not recognise native antigens
YY Y Y YYY
BY
T
Y
T
Proliferation and antibody production
No proliferationNo cytokine release
Cross-linking of surface membrane Ig
Y
B
Y
B Y
B
Y
B
Y
B Y
B
Y
BYY
B
Cell surfacepeptides
of Ag
Antigens must be processed in orderto be recognised by T cells
YT
T cellresponse
No T cellresponse
No T cellresponse
No T cellresponse
No T cellresponse
Solublenative Ag
Cell surfacenative Ag
Soluble peptides
of Ag
Cell surface peptides of Ag presented by cells that
express MHC molecules
ANTIGENANTIGENPROCESSINGPROCESSING
APCAPC
Contents
Part Introduction--conceptsⅠ Part Characteristics of APCs Ⅱ Part Ag Processing and presentation Ⅲ
Part Introduction--conceptsⅠEndogenous Ags: antigens synthesized within cells, including
self and unself protein----class MHC molecules.ⅠExogenous Ags: antigens comes outside the cells, including
self and unself protein----class MHCⅡ molecules.
Antigen processing: the conversion of native proteins to peptides which can combine with MHC molecules.
Antigen presentation: the course of formation and display of
peptide-MHC complexes on the surface of APCs and the course of peptide-MHC complexes recognition by T cells.
Ag capturing----Endocytosis (internalization)
Phagocytosis, Pinocytosis, Receptor-mediated endocytosis
Production of endogenous Ags and exogenous Ags
YThe site of pathogen replication or mechanism of antigen uptake
determines the antigen processing pathway used
Y
Cytosolic compartmentEndogenous processing(Viral, tumor antigens )
Vesicular CompartmentContiguous with extracellular fluid
Exogenous processing(Streptococcal, tumor antigens)
INTRACELLULAR REPLICATION
EXTRACELLULAR ORENDOSOMAL REPLICATION
Cell surfacepeptides
of Ag
Antigens must be processed in orderto be recognised by T cells
YT
T cellresponse
No T cellresponse
No T cellresponse
No T cellresponse
No T cellresponse
Solublenative Ag
Cell surfacenative Ag
Soluble peptides
of Ag
Cell surface peptides of Ag presented by cells that
express MHC antigens
ANTIGEN PROCESSING
APCAPC
Antigen-Presenting Cells (APC)
APC (Accessory cells) : A group of cells play important roles in the immune response which can uptake, process antigens and present peptide-MHC complexes to T cells.
Professional APC: express classⅡMHC molecules Dendritic cell Macrophage B lymphocyte Facultative APC: endothelial cells, epithelial cells,
fibroblast, etc
APC
• Express class , MHC moleculesⅠ Ⅱ and co-stimulatory molecules
• Uptake, process endogenous/exogenous antigens and present peptide-MHC to T cells
• Including dendritic cells, macrophages and B cells
Part Characteristics of APCsⅡ
Dendritic cell (DC) Macrophage B lymphocyte
1. Dendritic cell (DC)
• History: DCs were first found by Steinman in 1973 , named for their special spinelike projections. DCs were cultured successfully in vitro in 1993 by Inaba.
• Characteristic: The most efficient APC, can present antigens to naive T cells to elicit primary immune response.
Fig2-4 Mature DC suspended in media by colony ( ×400 )
Fig2-5 scattered mature DC ( ×400 )
Scanning electron micrograph
1. Dendritic cell (DC)
(1) Identification of DC: Typical morphology—spinelike projection MLR—stimulate naïve T cells activation Surface markers : CD1a, CD11c, CD83(human) high expression of classⅡMHC co-stimulatory molecules--CD80,CD86 others—CKs, CAMs, R(2) Source of DC: pluripotent hematopoietic stem cells myeloid DC myeloid progenitor lymphoid DC lymphoid progenitor
GM-CSF, IL-4
1. Dendritic cell (DC)
(3) Classification of DC : DC in lymphoid tissue:
Interdigitating DC (IDC) ,
Folicular DC (FDC) DC in non lymphoid tissue:
Langerhans cell (LC) DC in body fluid: Veiled cell, Blood DC
Interdigitating DC( IDC )
Express high level of class , MHC molecules and B7Ⅰ Ⅱ , lack of FcR and CR, can stimulate T cells.
FDC
B cell
Folicular DC ( FDC )
Lie in follicle of LN, no expression of class ⅡMHC, high level of FcR and C3bR.
Langerhan’s cells(LC)—Birbeck particle
Lie in the epithelia of the skin, gastrointestinal and respiratory tracts, express FcR and C3bR. After uptaking antigens, migrating to draining LN and becoming IDC.
1. Dendritic cell (DC)
(4) Development and Maturation of DC
Pre-DC phase
Immature DC ( iDC ) phase
Migration phase
Mature DC ( mDC ) phase
Pre-DCBlood
Non-lymphoid tissueDifferentiation
ImmatureDC
DistributeWidely distributed in the body
Possess ability of Ag capture and process
Cytokines and Ag
DC mature and move into lymphoid tissue
Ability of Ag capture and processing decreases while its ability of Ag presenting increases
Difference between iDC and mDC
• Ability of uptaking and processing antigens decreases.
• Ability of antigen presentation increases.• Express high level of MHC, co-stimulatory
molecules(CD80,CD86), CAMs(ICAM-1).• Ability to stimulate naïve T cell activation
increases.
1. Dendritic cell (DC)
(5) Antigens capturing:
• Phagocytosis—cell, bacteria
• Pinocytosis—soluble antigen
• Receptor-mediated endocytosis
FcγRⅡ, C3bR, mannose receptor
(6) Function of DC :
• Capture, process, present antigens—APC
• Stimulate T or B lymphocytes—mature DC
• Induce immune tolerance—immature DC
1. Dendritic cell (DC)
2. Macrophage ( MФ)• Stem from monocytes in blood
• Have strong phagocytosis (big phagocyte)
• Can not stimulate naïve T cells
• Capture antigens by phagocytosis, pinocytosis, receptor-mediated endocytosis
Function : • Phagocytosis
• Presentation of antigens Unactivated macrophage
Activated macrophage:
Class MHC molecules Ⅱ and co-stimulatory molecules
2. Macrophage ( MФ)
3. B cells
Functions
• Mediate humoral immune response
• Immunological regulation
• Present antigens to T cell
Soluble Ag--pinocytosis
Specific receptor-mediated endocytosis
The three kinds of professional APC
Cell surfacepeptides
of Ag
Antigens must be processed in orderto be recognised by T cells
YT
T cellresponse
No T cellresponse
No T cellresponse
No T cellresponse
No T cellresponse
Solublenative Ag
Cell surfacenative Ag
Soluble peptides
of Ag
Cell surface peptides of Ag presented by cells that express MHC antigens
ANTIGEN PROCESSING
APCAPC
Part Ag Processing and PresentationⅢ
Class MHC pathway ------exogenous antigensⅡ
Class MHC pathway ------endogenous antigensⅠ
Cross – presentation of antigen
Section Class MHC pathwayⅠ Ⅱ 1. Capture of exogenous Ag
2. Processing of Ag
3. Synthesis and transportation of class Ⅱ MHC molecules
4. Peptide loading of classⅡ MHC molecules
5. Presenting to CD4+T cells
1. Capture of exogenous Ag
• Endocytosis:
Phagocytosis: particles or granules
Pinocytosis: soluble antigens
Receptor-mediated endocytosis:
• Form endosome
Y Y
Pinocytosis
Phagocytosis
Membrane Igreceptor mediateduptake
Y
Uptake of exogenous antigens
Complement receptormediated phagocytosis Y
Fc receptor mediated phagocytosis
2. Processing of Ag
endosome + lysosome
Ag antigen peptides(10-30aa) Cathepsin
Endosomes
Exogenous pathway
Cell surface
To lysosomes
UptakeProtein antigens
In endosome
Cathepsin B, D and L proteases are activated by the decrease in pH
3. Synthesis and transportation of class MHC Ⅱmolecules
Synthesis of class MHC molecules in ERⅡ
Ii chain --- class MHC moleculeⅡ (Ii3α3β3 ) ①Promote formation of class Ⅱ MHC dimer ②Preventing endogenous peptide from combining with
classⅡMHC molecules within ER
③Leading classⅡMHC molecules into endosome from ER
Endosome (MIIC)
*Ii chain: Ia-associated invariant chain
A peptide of the invariant chain blocks the MHC molecule binding site.This peptide is called the CLass associated Ⅱ Invariant chain Peptide (CLIP)
Invariant chain CLIP peptide
and b chains of MHC class II molecules
CLIP
Need to prevent newly synthesised, unfolded self proteins from binding to
immature MHC
Invariant chain stabilises MHC class II by non- covalently binding to the
immature MHC class II molecule and forming a nonomeric complex
In the endoplasmic reticulum
MHC class II maturation and invariant chain
Ii c
hain
CLIP
4. Peptide loading of class MHC moleculesⅡ
Ii - class MHC moleculesⅡ
protease Ii chain cleaving
CLIP - class MHC moleculesⅡ
HLA-DM CLIP releasing
Antigen peptide - class MHC complexesⅡ
Endosomes
Cell surface
Uptake
Class II associated invariant chain peptide (CLIP)
(inv)3 complexesdirected towardsendosomes byinvariant chain
Cathepsin L degrades Invariant chain
CLIP blocks groove in MHC molecule
MHC Class IIcontaining vesiclesfuse with antigen
containing vesicles
Removal of CLIP
?
How can the peptide stably bind to a floppy binding site?
Competition between large number of peptides
HLA-DM catalyses the removal of CLIP
MIIC compartment
HLA-DM
Replaces CLIP with a peptide antigen using a
catalytic mechanism (i.e. efficient at sub-
stoichiometric levels)
Discovered using mutant cell lines that failed to
present antigen
HLA-DO may also play a role in peptide exchange
Sequence in cytoplasmic tail retains HLA-DM in endosomes
HLA-DMHLA-DR
5.Presenting to CD4+T cells
Antigen peptide-class MHC molecuelsⅡ presented on cell membrane by exocytosis
MIIC compartment sorts peptide-MHC complexes for surface expression orlysosomal degradation
Surface expression of class II MHC -peptide complexes
Exported to the cell surface (t1/2 = 50hr)
Sent to lysosomes for degradation
CD4+T cells
Section class Ⅱ MHC pathwayⅠ
1. Processing of endogenous Ag
2. Transporting of antigen peptide into ER
3. Peptide loading of class MHC moleculesⅠ
4. Presenting to CD8+T cells
1. Processing of endogenous Ag
• Proteosome : 20S, 26S
• Low molecular weight polypeptide (LMP) :
LMP2, LMP7 , LMP10
• Ag antigen peptides (6-30aa)
Degradation in the proteasome
The components of the proteasome include LMP2, LMP7, MECL-1 ( LMP10 )
*MECL-1 : Multicatalytic endopeptidase complex subunit
Cytoplasmic cellular proteins, including non-self proteinsare degraded continuously by a multicatalytic protease
Binding ubiquitin
2. Transporting of antigen peptide into ER
TAP(transporter associated with antigen processing):
Consisting of TAP1 and TAP2 ATP dependent transporter
Selective transporting (8-15aa)
ENDOPLASMIC RETICULUM
CYTOSOL
Peptide antigens produced in the cytoplasm are physically separated from newly formed class I MHC
Newly synthesisedclass I MHC molecules
Peptides needaccess to the ER in
order to be loaded onto class I MHC molecules
ER membrane
Lumen of ER
Cytosol
Transporters associated withantigen processing (TAP1 & 2)
Transporter has preference for >8 amino acid peptideswith hydrophobic C termini.
TAP-1 TAP-2
Peptide
TAP-1 TAP-2
PeptideTAP-1 TAP-2
Peptide
TAP-1 TAP-2
PeptideTAP-1 TAP-2
Peptide
TAP-1 TAP-2
PeptideTAP-1 TAP-2
Peptide
TAP-1 TAP-2
PeptideTAP-1 TAP-2
Peptide
TAP-1 TAP-2
Peptide
ER membrane
Lumen of ER
Cytosol
TAP-1 TAP-2
Peptide
ATP-binding cassette(ABC) domain
Hydrophobictransmembranedomain
Peptide antigensfrom proteasome
3. Peptide loading of class MHC moleculesⅠ ER: antigen peptide—class MHC complexesⅠ
Endoplasmic reticulum
Calnexin bindsto nascent
class I chainuntil 2-M binds
TAP-1 TAP-2
Peptide
TAP-1 TAP-2
PeptideTAP-1 TAP-2
Peptide
TAP-1 TAP-2
PeptideTAP-1 TAP-2
Peptide
TAP-1 TAP-2
PeptideTAP-1 TAP-2
Peptide
TAP-1 TAP-2
PeptideTAP-1 TAP-2
Peptide
TAP-1 TAP-2
PeptideTAP-1 TAP-2
Peptide
B2-M binds and stabilises
floppy MHC
Tapasin, calreticulin, TAP 1 & 2 form a complex with
the floppy MHC
Cytoplasmic peptides are loaded onto the
MHC molecule and the structure becomes
compact
Maturation and loading of class I MHC
4. Presenting to CD8+T cells Antigen peptide-class Ⅰ MHC molecuels presented on cell membrane by exocytosis
Fate of class I MHC
Sent to lysosomes for degradation
Exported to the cell surface
Ag(cytosolic protein)
Proteasome proteolytic degradation
Ag peptide
TAP complex transporting into ER
antigen peptide-class Ⅰ MHC complexes
Golgi complex exocyotsis
Presenting to CD8+T cells
CD8+T cells
CD8+T cells
CD4+T cells
Section Cross-presentation of antigensⅢ
Cross-priming:
• Class MHC molecules also present exogenous Ⅰantigens to CD8+T cells
• Class MHC molecules also present endogenous Ⅱantigens to CD4+T cells
CD4+T cell(Th) CD8+T cell(Tc)
T cellReceptor
Peptide
MHCClass II
T cellReceptor
Peptide
MHCClass I
Antigen PresentingCell
Target cell
CD4 CD8