Download Introduction to Blood

Infection and Immunity
NK cells
APC and antigen presentation
Weilin Chen, Ph.D
Institute of immunology, ZJU
[email protected]
Contents
• NK cells
– Development，receptors and function
• Antigen presenting cells
– Dendritic cells
• Antigen presentation
– Four pathways
Natural killer cells
• Development
• Receptors
• Function
NK cells development
Bone marrow
Blood
- In the bone marrow, a common lymphoid progenitor gives rise to the
antigen-specific lymphocytes of the adaptive immune system (B and
T cells), as well as to a type of lymphocytes that is antigen nonspecific; the Natural Killer (NK) cell lineage (express the NK lineage
marker, NK1.1).
- As NK cells are antigen independent, they belong to the innate
immune system.
- Mature NK cells that circulate in the blood stream are larger than B
and T cells.
- They contain a distinctive granular cytoplasm. The release of the
lytic granules contributes to the killing of cells infected with
distinctive viruses, such as herpes virus.
- NK cells also contribute to the killing of abnormal tumor cells,
without prior immunization or activation.
NK cells development
NK cells development
In vitro
NK cells development
NK receptors
Activation of NK cells is the net effect of inhibitory and activating signals
The “Missing Self” Hypothesis
• States that altered expression/down-regulation of
MHC Class I on target cells leads to spontaneous
NK-mediated destruction of the target cell
• Down-regulation of MHC Class I OR overexpression of NK cell activating molecules leads
to NK cell-mediated killing of target cell
Hypothesis：Non-self ；
induced self
NK receptors: ‘Defense is the best offense”
While both KIRs and KLRs sense the
presence (absence) of MHC class I
molecules, activating as well as inhibitory
receptors are found in both families of
receptors.
- The KIRs are subdivided according to the
number of immunoglobulin-like domains
(2 or 3 domains) and the length of their
cytoplasmic tail: Short tail = activating
receptors
Long tail = inhibitory receptors
- The KLR are heterodimers of CD94
associated with a NKG2 molecule. Six
distinct NKG2 isoforms exist in humans.
NKG2C/CD94 = activating receptor
NKG2A/CD94 = inhibitory receptor
NKG2B/CD94 = inhibitory receptor
NKG2D homodimer = activating receptor.
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Functions
Release of cytotoxic granules at the site of contact with infected cells
NK cell
Target cell
- First contact between a CTL or NK cell with infected cells is via non-specific binding of adhesion
molecules (LFA-1 (blue) on T and NK cells with ICAM-1 or ICAM-2 (brown) on target cells). This makes
a channel between the target and the cytotoxic cell.
- Specific antigen/MHC class I recognition by TCR on CTL, or engagement of the NK’s natural
cytotoxic receptors (NCR) (green) by non-MHC ligands (orange) on the surface of the target cell. This
results in a polarization of the cell: the actin cytoskeleton (green staining in the immunofluorescence
microscopy) at the site of contact is reorganized as to aligning the microtubule-organizing center
(MTOC), as well as the secretory apparatus, including the Golgi (GA). The GA-derived lytic granules
(stained in red in the photomicrograph) are specifically directed onto the target cell.
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- The content of the granules is directly released onto the target cell.
Why are NK cells prominent tumor killers?
Similar to many pathogens, tumor
cells can escape the adaptive
immune system, by downregulating
the expression of MHC class I.
This makes them more susceptible
to NK cells.
- The regression of transplanted tumors in a normal mouse model (blue line) is largely due to the action of CTLs recognizing
tumor antigens presented on MHC class I (right panel). Albeit the presence of NK cells, this regression is absent in nude mice (red
line) in which CTLs do not develop.
-Tumor variants that express low levels of MHC class I become susceptible to NK cells, especially in nude mice (have higher levels
of NK cells than wild type mice). Thus tumors that are sensitive to NK killing grow less well in nude than normal mice (central
panel).
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- Transfection of MHC class I genes resulting in high expression of this protein restores NK cell resistance but susceptibility
CTL in normal mice (left panel; blue line).
Antigen presenting cells and
antigen presentation
Antigen presenting cell, APC
A variety of cell types which carry
antigen in a form that can stimulate
lymphocytes.
professional APC:MΦ,DC,B
non-professional APC
Target cells
The 3 types of professional APCs
Constitutively express a
high level of MHC II
and the co-stimulatory
protein,B7. the most
effective APC
must be activated by
the process of
phagocytosis before
expressing class II
MHC and B7.
Constitutively express
class II MHC but must
be activated to
produce B7.
Dendritic cells (DC)
Dendritic cells were first described
by Paul Langerhans (Langerhans
cells) in the late nineteenth
century. It wasn't until 1973,
however, that the term "dendritic
cells" was coined by Ralph M.
Steinman.
Sources of DCs
多能造血干细胞
HSC
Lymphoid progenitor
Myeloid髓系前体细胞
progenitor
淋巴系前体细胞
DC
髓系DC
Mo
单核细胞
PMN
中性粒细胞
GM-CSF
TNF-a
IL-4
NK
T
NK细胞 T细胞
B
DC
B细胞 淋巴系DC
DC
髓系DC
巨噬细胞
macrophage
Subset of DCs
Conventional DCs ，cDC
Plasmacytoid DCs，pDC：anti viral infection
Maturation of DCs
LPS
IL-1,TNFα
B
Menu
F
Function of DCs
antigen presentation, immune activation, immune tolerance
Antigen presenting cells
mononuclear phagocyte system, MPS
1.Differentiation and distribution
2. Surface markers
3. function
Differentiation and distribution of MPS
Bone marrow
HSC
Myeloid
progenitor
Pre-monocyte
monocyte
Blood
monocyte
tissues
macrophage
Mononuclear phagocyte system, MPS
1. Surface markers:
MHC-I/Ⅱmolecules
CKR: M-CSFR
CAM: LFA-1,ICAM-1,B7,CD40
FcR, CR1/3/4
2. secretion：
-enzymes: lysosome , myeloperoxidase
-cytokines (IL-1,TNF,IL-12)
-complement:C1～C9, Bf
-coagulation factor, PG, LTs, ACTH, etc.
Biological functions of MPS
 Phagocytosis
 antitumor：indirect or direct killing, ADCC;
 participating in immune response：
-Ag presenting, providing the second signal；
-CMI
 participating in immune regulation:
-positive regulation：secrete IL-1/12，TNF-α
-negative regulation：PG, TGF-β
 Mediating inflammation: phagocytosis, secrete
inflammation medium
phagocytosis
B Cells (BCR)Take Up Antigen into
Vesicles
andpresenting
Present Peptide
Antigen
cells
Fragments from Proteins
B cells
in MHC-II
The properties of various APCs
Antigen presentation
• Definition
• Ag presentation
-MHC class I molecule pathway
-MHC class II molecule pathway
- Cross-presentation pathway
- CD1 molecule pathway
Antigen capturing
• Phagocytosis
• Pinocytosis
• Receptor-mediated endocytosis
Antigen processing
The conversion of an antigen into
a form in which it can be
recognized by lymphocytes.
Antigen presentation
The process by which certain cells in the
body (APC) express antigen peptideMHC molecule complex on their cell
surface
in
lymphocytes.
a
form
recognize
by
sources of antigens
* exogenous antigen
* endogenous antigen
The site of pathogen replication or mechanism of antigen uptake
determines the antigen processing pathway used
Y
Extracellular or
Endosomal replication
Vesicular Compartment
Contiguous with extracellular fluid
Exogenous processing
(Streptococcal, Mycobacterial antigens)
Intracellular replication
Cytosolic compartment
Endogenous processing
(Viral antigens)
Distinct mechanisms of antigen generation are used to raise
T cells suited to the elimination of endogenous or exogenous pathogens
Pathogens in Cytosol/Vesicles
The pathway of MHC I -associated endogenous
Ag presentation
endogenous antigen（such as virus Ag, tumor Ag)
cytoplasm
degraded by proteasome
antigen peptide（8-13 AA）
transported to endoplasmic reticulum by TAP
Peptide/MHC-I molecule complex
to surface of APC
submit to CD8+T
Degradation in the proteasome
Cytoplasmic cellular proteins, including non-self proteins
are degraded continuously by a multicatalytic protease of 28 subunits
Transporters associated with
antigen processing (TAP1 & 2)
Hydrophobic
transmembrane
domain
Lumen of ER
Peptide
ER membrane
Cytosol
Peptide
Peptide
Peptide antigens
from proteasome
ATP-binding cassette
(ABC) domain
Transporter has preference for >8 amino acid peptides
with hydrophobic C termini.
Maturation and loading of MHC class I
Peptide
Peptide
Peptide
Endoplasmic reticulum
Calnexin binds
to nascent
class Ia chain
until 2-M binds
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
B
Menu
F
B
Menu
F
The pathway of MHC II -associated exogenous Ag
presentation
Exogenous antigen
newly synthesised MHC class II molecule
Phagocytosis, pinocytosis,
（in the endoplasmic reticulum ）
FcR-phagocytosis
early endosome
li binds in the groove of MHC class II molecule
lysosome
late endosome
protease MIIC
li
degrade
protease
Degrade into 1318AA peptide +
MHC class II molecule
Ag peptide/MHC class II molecule complex
transport to the surface of APC, recognized by CD4+T
Uptake of exogenous antigens
Membrane Ig
receptor mediated
uptake
Y
Phagocytosis
Complement receptor
mediated phagocytosis
Pinocytosis
opsonization
Y
Fc receptor mediated phagocytosis
Exogenous pathway
Uptake
Protein antigens
In endosome
Endosomes
Increase
in acidity
To lysosomes
Cathepsin B, D and L proteases are activated by the decrease in pH
Proteases produce ~24 amino acid long peptides from antigens
Drugs that raise the pH of endosomes inhibit antigen processing
The functions of Ii:
 involve in the assembling and folding of MHC class
II molecule;
 Block the groove of MHC class II molecule;
 Lead the assembled class II molecule to MⅡC.
CLIP：class II-associated invariant chain peptide
B
Menu
F
B
Menu
F
Cross-presentation
• Class I MHC molecules present exogenous Ags
to CD8+ T cells
• Class II MHC molecules present endogenous
Ags to CD4+ T cells
• Cross-presentation of Ags by DC plays an
important role in anti-viral infection and antitumor immunity.
NKT cells.
CD1 molecular pathway
Antigen presentation
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