Linking innate and adaptive immunity Flashcards
(103 cards)
1
Q
2 types of DC
A
Plasmacytoid dendritic cell
Conventional dendritic cell (cDC)
2
Q
pDC
A
Only involved in innate immune response
Very high level of PRRs
Stay at the site of infection
Capable of producing large amounts of type I IFN (antiviral cytokines)
Amplify local response
3
Q
cDC
A
Travel to lymphoid tissue once activated
Activate T cells in lymphoid tissue
Classic APC
4
Q
Activation of DC
A
Interaction between PAMPs and PRRs activates DCs
5
Q
unactivated(immature) DC
A
Many dendrites
Phagocytosis
6
Q
Activated DC in lymphatic vessel
A
No longer phagocytic
Increase the expression of receptors and adhesion molecules target DC to lymphatics and lymphoid tissues (migration)
Travel via lymphatic vessels
7
Q
Activated DC in secondary lymphoid tissue
A
Increases processing of antigen
Express peptide:MHC and costimulatory molecules
Interacts with T cells to activate them
8
Q
secondary lymphatic organ
A
lymph node, spleen, Peyer’s patch
9
Q
Priming naïve T cells
A
first contact the T cell with their antigen
10
Q
and 2 types of T cells
3 signals to activate T cells
A
CD4 and CD8
pMHC:TCR (MHC with processed pathogen peptide bind with TCR)
Costimulation (B7.1 and B7.2 bind with CD28)
Cytokines (determine the differentiation of T cells)
11
Q
entry the lymph node
A
DCs enter lymph node via afferent lymphatics
T and B cells enter through High Endothelial Venules (HEV) from blood circulation
HEV: post-capillary venules found in lymph nodes
11
Q
exceptions
DC antigen presenting in lymph node
A
If the antigens from the virus rapidly kill the DCs, they can transfer the antigen to resident DCs in the lymph nodes
If cDCs are absent, tissue-resident macrophages with DC morphology (LCs) are responsible for initial uptake and transport and can then transfer the antigen to resident DCs in lymph node
12
Q
T cells in lymph node
A
Naïve lymphocytes are constantly scanning for their specific Ag that they can respond to
13
Q
if T cells encounter the antigen
A
stay in lymph node
Get activated, then proliferates and differentiates until the whole process complete
Effector T cells exit lymph node via efferent lymphatics
Chemokine receptors and adhesion molecules lead them home to infected tissue
14
Q
If there is no match antigen for T cells
A
exit and return to the blood to restart the search
leave via efferent lymphatics
15
Q
PRR signaling and antigen presenting of DC does not happen all in the same place or time
A
16
Q
general process and key molecule
T cell entry into lymph node
A
chemokine and adhesion molecues
selectin （Rolling）–> chemokine （activation）–> integrins （tight binding）–>chemokine （diapedesis）
17
Q
selectin
A
adhesion molecule
binding →rolling along the endothelial surface targeting them to lymphoid tissue
light attachment between T cells and HEV
Different tissues express different molecule
18
Q
Chemokine in T cells migration
A
binding chemokine receptor
CCL19 & CCL21 bind to CCR7 on T lymphocytes lead to activation of integrins
19
Q
integrin
A
adhesion molecule
binding causes tight binding and lymphocyte to migrate
20
Q
rolling
A
mediated by selectins
21
Q
activation
A
by chemokines, activate integrin
22
Q
arrest and tight binding (adhesion)
A
mediated by integrin interaction
23
Q
diapedesis
A
transendothelial migration
cross the endothelium and enters the lymph node
24
in lymph node, () scan for (), DC secrete () to attract () to them
T cells, antigen, chemokines, T cells
25
long T cell/DC interaction
Naïve T cells arrest their movements after engaging Ag:MHC
Kinetics of early encounters depends on quality, quantity, availability of Ag and activation state of a DC
T cells become involved in committed, long-term (8 hours or more) relationships with DCs
26
immunological synapse
interaction between 2 immune cells
27
timing of events
early hours: innate immune response, APC activation
minutes to 24 h: antigen entry
1-24h: T cell/APC interactions (T cells can spend 1 –24 hrcirculating and looking for their antigen)
1-4 days: T cell proliferation and differentiation (T cells can experience proliferation and differentiation over the following ~ 4 days)
3-4 days: egress(使外出) of effector cells
## Footnote
DC can be surveyed by more than 5000 T cells per hour
28
immune system is dynamic
production of cytokine and NK cells function and T cells function can have overlap (happen paralell)
Balancing cell generation in primary lymphoid organs with activation, proliferation and differentiation in secondary lymphoid organs
Constantly dealing with microinjury, tissue repair and microbiota
## Footnote
Many events happening in parallel. Many of the processes overlap over time, can change locations & influence each other
29
T cells
Types of lymphocytes
Arise in the thymus from bone-marrow progenitors
Most adaptive immune responses require activation of T cells
T cells can **ONLY** recognize peptide fragments of the Ag bound to **selfmolecules** of the Major Histocompatibility Complex (MHC)
These peptide-MHC complexes are expressed on the plasma membrane of Antigen-Presenting Cells (APC)
30
clusters of differentiation
Lymphocytes appear very similar, but different sets carry different clusters of differentiation (CD) co-receptors on their surface
31
CD8+ T cells
become effector Cytotoxic T lymphocytes (CTLs)
recognize antigens on MHC I
32
CD4+ T cells
Helper T cells
can be divided into distinct subsets
recognize Ag on MHC II
at least 5:
TH1
TH2
TH17
TREG
TFH
Each produces a distinct cytokine profile and regulates distinct activities within the body
33
link between type of PAMP and type of T cells is going to arise
The activation signals sent to T cells are highly dependent on the PAMP that the dendritic cell has been exposed to.
Will influence the type of cytokines produced, leading to the type of effector T cell that will arise
34
TCR complex
TCR
CD3
z (zeta) chain
ITAMs
35
ITAMs
immunoreceptor tyrosine-based activation motif
36
# just the TCR part
TCR recognition subunit
heterodimer
transmembrane
not secreted
2 types:
alpha, beta (major)
delta, gama (<10%)
has a variable (top) and a constant region (bottom)
37
# gene segments, position
BCR and TCR undergo DNA rearrangement
gene segments: V, D, C, J
Variable, diversity, joining segments, and constant genes
alpha chain: V, J, C domain
beta chain: V, D, J, C domain
TCR rearrangment occurs in the thymus
38
somatic recombination or gene rearrangement
recombination of gene segments in T cell receptor genetic loci to produce functional gene
39
interaction between TCR and pMHC
TCR recognize both the peptide and the MHC complex
40
types of APC
**professional APC**: DCs, macrophages, activated B cells
1.express MHC class I and II
2.express costimulatory molecules when activated
**non-professional APC**: all nucleated cells in the body
1.express MHC class I under normal conditions
2.do not express costimulatory molecules
41
MHC class I
bind and present peptides generated within the cell (including self protein)
ie. endogenous peptide
activate CD8+ T cells (cytotoxic function)
1 alpha chain (transmembrane, 3 domains), 1 beta microglobulin (non-transmembrane and invariant, constant, hydrophobic interaction, no covalent binding)
42
MHC class II
bind and present peptides of extracellular origin
ie. exogenous peptide
activate CD4+ T cells (helper function)
alpha chain (2 domain) and beta chain (2 domain), both transmembrane
43
peptide binding in MHC
MHC first bind the peptide and them express on the cell surface
44
# overall structure
general features of MHC （I）
Each chain of the MHC has **several Immunoglobulin (Ig)-like domains**
– A modular secondary structure shared among many molecules of the immune
system (adhesion molecules, T cell receptors)
– Consists of a domain of ~100 amino acids, **alpha helices (peptide binding part)**, beta sheets, stabilized by **intrachain disulfide bonds**
45
# each part
general features of MHC （II）
**Ag peptide-binding cleft or groove facing out**
**More conserved area facing the cell membrane**
MHC have allele-specific differences in their primary sequence: **these differences are located mostly around in the peptide-binding cleft**
Peptide binding groove of both MHC-I and II have alpha helices and beta sheets
46
Peptide binding to MHC
MHC class I molecules bind short peptides of 8-10 amino acid
MHC class II can bind a peptide that at least 13aa long
difference due to the shape difference (MHC I shape is close off, limit the size)
47
co-receptors
TCR-pMHC interaction is a rather low affinity interaction
co- receptors (CD 4 and 8) physically interaction with the MHC molecules (**the constant region**)
48
CD4
Single chain Transmembrane protein
4 Ig-like domains
49
CD8
Heterodimer
Linked by disulfide bond
Each chain has 1 Ig-like domain
Both chains are Transmembrane proteins
50
function of coreceptor
initiating the intracellular signaling for TCR (signal 1)
bind MHC and enhance the affinity of the TCR-pMHC interaction
51
# general + endogenous processing
MHC I antigen processing and prestatation pathway
requires cytosolic or endogenous processing
endogenous pathogens: mediate their own entry into cell (wants to get into the cell)
ex. virus, intracellular bateria and parasite
peptide generated by proteasomes (ubiquitin labeled protein digest by proteasomes) (**polyunibiquinaiton**)
also process self protein to inhibit the activity of NK cells
52
# pathogen
MHC II antigen processing and prestatation pathway
requires cytosolic or exogenous processing
pathogens are taken up by immune cells by phagocytosis or endocytosis by engulfment
entry of these pathogens is mediated by the immune cells
(ex. bacteria, parasites, fungi)
peptides are generated form internalized antigens in **endocytic vesicles** (taken in within **endosomes**, which fuse with lysosome, contents are degraded)
at the same time MHC II are produced and exported from the ER in vesicles
53
process of MHC I antigen presenting
in the ER
formation of MHC I and generation of peptide happen in parallel
4 steps
54
step 1 of MHC I antigen presenting
MHC class I folding (alpha chain held in place by **calnexin**)
55
step 2 of MHC I antigen presenting
alpha chain released from calnexin
alpha chain interact with beta microglobulin (**calreticulin, ERp57 help**)
partly folded MHC bind to **tapasin** (chaperone) to link it to **TAP**
proteins are tranlated in the cytosol and unbiquitinated (only 30%)
56
Step 3 of MHC I antigen presenting
polyunbiquinated protein get degraded by proteasome in cytosol
**peptide fragments are brought into ER by TAP**
**ERAAP** trims peptide that are too long to bind to MHC
peptide bind with MHC I will allow MHC I properly fold
57
Step 4 of MHC I antigen presenting
Peptide binds to peptide binding groove of MHC I
MHC I folding is complete
pMHC-I released from TAP
pMHC-I targeted for cell membrane
58
MHC II vesicle
MHC II fored in ER
Invariant chain (Ii) binds to peptide groove
59
function of Ii
Ii guides transport of class II MHC molecules to endocytic vesicles
Ii also uses sorting signals in its cytoplasmic tail to direct "MHC class II molecule–containing vesicles" to "peptide-containing endocytic compartments"
Ii prevents peptides from binding to the groove too early in the ER
later when the vesicle acidifies, Ii start to break , leaving CLIP bind with MHC II
60
step 1of peptide loading
Ii in complext with MHC II, prevent other peptide binding (**in ER and endocytic vesicle**)
61
step 2 of peptide loading
acidification, Ii degraded, leaving CLIP bound to MHC II
62
step 3 of peptide loading
2 vesicle fuse together, but peptide still can't bind MHC II because CLIP is blocking
63
step 4 of peptide loading
HLA-DM: always in the vesicle from the very beginning
HLA-DM bind with MHC II, **stabilize it and releases CLIP**
peptide then bind to the peptide binding groove of MHC II
pMHC II target cell surface
64
HLA-DM
human leukocyte antigen-DM
MHC class II like molecules, similar structure but no peptide binding groove
65
Exceptions of MHC peptide presenting
1. Cross-presentation
2. presentation of cytosolic peptides by MHC class II
3. allorecognition
66
# which cell, what, examples, how
cross presentation
demdritic cells (only APC do this)
redirect exogenous antigens to endogenous pathway (on MHC I)
examples:
1.virus phagocytosed by DC (exogenous but released in cytoplasm go through endogenous pathway)
2.virally-infected cells (present DAMPs), phagocytosed by other cells, viral peptide presented on MHC I
actual redirection machnism is unclear
exogenous antigen--present on MHC II--activate CD4+ T cell--cytokine--redirect to MHC I -- activate CD8+ T-cell response
67
presentation of cytosolic peptides by MHC Class II
occurs via autophagy
**autophagosome**: specialized double membrane vesicle that contain cytoplasmic content and fuses with lysosomes
autophagosome fuse with MHC II vesicle
example:
1.infected macrophage weaken by pathogens, present MHC II bind with TH1 which activate macrophage to kill to pathogen
2.some viruses prevent presentation on MHC I
68
allorecognition
**recognition of non-self MHC by some T-cells in the body**
1 to 10% of all T cells in an organism can react to allogeneic (non-self) MHC (allo-MHC)
allorecognition is the main mechanism of rejection of transplanted organs between genetically different individuals of the same species
69
MHC restriction
TCRs are not only specific to peptide but also specific to MHC
T cell is able to recognize a **specific peptide** only when bound to a specific **SELF MHC molecule**
70
2 types of allorecognition
**1.direct
T-cells directly recognize the non-self MHC**
Recipient T cell recognition of donor/transplant MHC molecules expressed on the surface of donor cells
**2.indirect
T-cells interact with the non-self MHC that present by a self MHC**
Recognition of processed donor peptides (donar cell pieces and the non-self MHC) presented onto the recipient’s own APCs via self-MHC
71
gene
segment of a chromosome that controls a specific characteristics
(encodes for protein)
72
allele
one specific form of a gene
73
locus
the specific chromosomal location of a gene
74
MHC genetic
MHC molecules are coded by **human leukocyte antigen (HLA) genes**
found in a cluster of genes on **chromosome 6** in human
75
2 main classes of MHC genes
1.MHC class I genes
HLA-A, HLA-B, HLA-C (encode alpha chian)
2.MHC class II genes
HLA-DR, HLA-DQ, HLA-DP, HLA-DM, HLA-DOA, HLA-DOB (encode alpha and beta chian)
76
polygeny
**Multiple genes with the same function, but slightly different structures** (ex. HLA-A, HLA-B, HLA-C)
results in a high degree of variance in MHC expression in the population
77
polymorphism
**Multiple variations (forms), or alleles, exists for each gene**
inherit 3 different MHC-I alleles from each parent, so 6 alleles can be expressed in one individual (HLA-A , HLA-B, & HLA-C allele per chromosome)
many MHC gene have more than 100 different alleles
allele known by number after the locus (ex.HLA-A2, HLA-DR3)
78
Haplotype
Particular combination of MHC alleles found on **a single chromosome**
Each individual inherits one haplotype from each parent
79
MHC alleles are () expressed
**codominantly**
-Both maternal and paternal MHC genes are expressed in offspring cells
-Best chance of presenting all the possible antigen peptides it encounters
80
() makes transplanation difficult
humans are heterozygous at each locus (usually will have different MHC)
81
Peptide Binding Groove Allelic Variation
Differences clustered at amino acid locations within the groove sites:
1. Helps facilitate presentation of different variety of peptides (different peptide binding specificities)
2. If the areas outside of the binding groove were altered too much, it can affect the structure conformation and folding of the MHC molecule
A given MHC molecule can bind numerous different peptides, and some peptides
can bind to different MHC molecules
82
# kinase
2 types of receptors
**intrinsic recetors**
intrinsic kinase activity
have their kinase domain
Signaling initiated by dimerization and transphosphorylation
**extrinsic recetors**
extrinsic kinase activity
recruit kinase
Signaling initiated by recruitment of kinase and dimerization followed by transphosphorylation
83
# binding domain and complex
SH2 domain
found in many proteins
**can recognize phosphorylated tyrosine on other proteins**
**Phosphorylated tyrosine (a.k.a. phosphotyrosines) are binding sites** for
a number of protein-interaction domains.
Formation of multimolecular complexes
around adaptor proteins.
only when complex complete it can have downstream effect
84
Phosphorylation and ubiquitination are key modifications involved in signaling
85
Kinases
proteins that phosphorylate other proteins
86
Phosphatases
proteins that dephosphorylate other proteins
87
How does TCR binding initiate
signaling?
1. pMHC:TCR binding occurs and coreceptor (CD4) binds MHC constant region
2. **Lck** phosphorylate ITAMs
3. **Zap-70** recruited to ITAMs, its SH2 domain bind with phosphorylated ITAM
4. Zap-70 is phosphorylated by Lck
88
Lck
Lymphocyte-specific protein tyrosine kinase
A co-receptor-associated kinase
phosphorylate ITAM and Zap-70
89
TCR signaling complex singal 1 process and effect
**Process:**
1. Co-receptor and TCR binding
2. Lck recruited
3. ITAM phosphorylated
4. Zap-70 recruited
5. Zap-70 binds to phosphorylated ITAMs
6. Zap-70 phosphorylated
7. Downstream signaling
**Effects:**
Many pathways activated in parallel
Leading to transcription of many genes
90
# 是什么做什么 有什么molecule
Signal 2 of TCR
Costimulation is required for T cell activation, survival and proliferation
Costimulatory ligands and receptors:
-**Ligands on APC**:
* CD80 (B7.1)
* CD86 (B7.2)
-**Receptor on T cell**:
* CD28
91
positive and negative costimulatory receptors
Positive costimulatory receptors—facilitate activation
- **CD28**
Negative costimulatory receptors—help turn activation off
- **CTLA-4, PD-1**
- lead to anergic T cells
92
CD28
**Transmembrane glycoprotein** expressed as a **homodimer**
Found on **all naïve T cells at baseline**
Binds B7.1 (CD80) and B7.2 (CD86), also homodimers, both expressed by **activated professional APCs**
non professional APC don't express co-stimulatory molecule
93
CD28 signaling take home
1. Binding to B7 molecules (CD80/86)
2. Triggers phosphorylation of CD28 receptor by a kinase
3. Recruitment of another kinase
4. Additional signaling
94
clonal anergy
absence of costimulation, T cells become anergic (nonresponsive)
Regulation and decrease the probability of autoreactive T cells (preventing uncontrolled proliferation of T cells)
anergic T cells can no longer respond to stimulation. once anergic, it's anergic forever
95
when does HLA-DM know when CLIP should be released
the pH will drop and at a certain low pH, HLA-DM changes conformation of MHC II to release CLIP
96
vesicle fusion specificity for MHC II and peptide vesicle
Ii and SNARE proteins: recognize and binding to proteins on target vesicles
97
IL-2
example of **autocrine type** of cytokine response system here:
T cell produce the cytokine and receptor for it
binding of IL-2 induces a very strong proliferation signal during activation stages
outcome:
activation and robust(强健的) proliferation
production of effector and memory clonal cell population
98
Singal 1 and 2 activate:
transcription of IL-2 gene and IL-2 R alpha gene (CD25, part of the receptor)
when no signal. there is no expression of IL-2 and IL-2 R alpha
IL-2 gene and IL-2 R alpha gene regulate seperately, 2 seperate gene
99
IL-2 R
beta, gamma chians are constitutively expressed on the cell surface. but low affinity for IL-2
IL-2 R alpha is available: higher affinity to IL-2
100
active T cell secrete and responde to IL-2
naive T cell: no IL-2 no IL-2 R alpha
T cell receive signal 1 and 2:
transcription of IL-2 and IL-2R alpha gene
IL-2 secreted
highe affinity to IL-2R expression
101
IL-2 secretion type
primarily autocrine
paracrin fashion for Tregs
Tregs donot produce their own IL-2 but have IL-2R alpha chain on their IL-2R, regulate the proliferation of T cells
102
Signaling from IL-2R results in proliferation and can help modulate T-cell differentiation for some T cell subsets
