10. Lymphocyte signalling 2 Flashcards
(54 cards)
1
Q
Why are receptors drug targets?
A
Because you don’t have to get things through the plasma membrane.
2
Q
What principles from the CD28 receptor family can be applied to other receptors?
A
- Receptors come in families
- There are activating and inhibitory receptors.
- Receptors contain protein interaction motifs like ITAM or ITIM.
- Signalling moves downstream through protein recruitment like TCR to Lck to ZAP70
3
Q
What is the structure of the BCR?
A
- It is simpler then the TCR
- It is a surface immunoglobulin that has the same light and heavy variable chains as the antibody it will produce.
- It has a short transmembrane anchor that doesn’t extend into the cytoplasm.
- It has 2 conserved signalling chains called Iga and Igß that contain 1 ITAM each and transduce the antigen recognition signal.
4
Q
What is the signalling mechanism of the BCR?
A
- Cross-linking of antigen recognition region causes the recruitment of src family kinase called Lyn or Fyn.
- Lyn phosphorylates the ITAMs.
- This recruits Syk family kinases.
- Syk provides the enzymatic activity associated with BCR activation.
5
Q
What are immunoglobulin superfamily receptors?
A
- This is the family that the TCR and BCR belong to.
- It is named for the immunoglobulin fold within the receptor structure.
- Other receptors in this family is FcR and NK cell receptors.
6
Q
What is the Fc Receptor?
A
- It binds the Fc domain of an antibody.
- It can activate or inhibit the cell it binds to.
- FcR are expressed on every innate cell for activation and on B cells to provide negative feedback.
- A function of Fc receptors includes opsonisation of pathogens to aid phagocytosis
7
Q
Where is the FcR expressed?
A
Innate immune cells:
1. Macrophages
2. Neutrophils
3. Eosinophils
4. Mast cells
5. NK cells
8
Q
Why are there lots of different Fc receptors?
A
To recognise different antibody classes.
9
Q
How do activating Fc receptors work?
A
- Function the same as BCRs and TCRs.
- They have separate signalling chain called the FC gamma chain.
- Fc gamma contains an ITAM.
10
Q
How do inhibitory Fc receptors work?
A
- Only on B cells
- For negative feedback
- This allows the B cell response to be terminated once the infection is cleared.
- Contains ITIMs that recruit phosphatases.
11
Q
What is the conserved signalling mechanism in the FcR?
A
- Activated by the antigen/antibody complex crosslinking the receptor.
- This causes the recruitment of Src kinases usually Lyn.
- Lyn phosphorylates the ITAMs.
- This causes the recruitment of Syk kinases called Syk.
- Syk provides the enzymatic activity for the FcR.
12
Q
How are Fc receptors used in drug design?
A
- When making anti-CTLA4 antibodies you bind 2 anti-CTLA4 to an Fc antibody fragment.
- The primary function of this is to bind to CTLA4 to prevent it binding CD80/86. This keeps T cells active.
- The secondary function is the anti-CTLA4 antibodies coat the surface of Treg cells meaning the Fc fragment faces outwards and is free to bind.
- This triggers APCs to undergo antibody dependant cellular cytotoxicity and delete Treg cells.
- This enhances the immune response.
- But it needs to be considered when you design drugs if you want the Fc region to be exposed
13
Q
What 2 signals are needed to activate NK cells?
A
- Activating receptors that engage stress proteins expressed on cells.
- inhibitory receptors that bind MHC1 and need to be released to activate an NK cell.
14
Q
How do the inhibitory receptors on NK cells work?
A
- It binds MHC1.
- They are critical to prevent damage to healthy cells. All healthy nucleated cells express MHC1.
- This means the default state of NK cells is inhibited.
- When a cell is not expressing MHC1, it means it has intracellular problems eg cancer or viral infection.
- This loss of MHC1 releases the inhibition of NK cells.
15
Q
How do the activating receptors on NK cells work?
A
- If the MHC1 is lost and the inhibitory receptor is released, the NK cell can be activated.
- A stress ligand expressed on the same cell can engage the activating receptor.
- This causes the full activation of the NK cell.
16
Q
How can you distinguish the activating and inhibitory receptors?
A
The activating receptors contain ITAMs and contain a positively charged transmembrane residue.
17
Q
What is the function of the positive residue in the NK cell receptor transmembrane region?
A
- It allows the NK receptor to associate with its signalling chains.
- The signalling chains are either DAP10 or DAP12.
- DAP10 and DAP12 have negative charges in their transmembrane domains.
18
Q
What is the signalling motif and protein recruited of DAP10?
A
Signalling motif: tyrosine X X methionine - YXXM (This is the same in CD28 and ICOS).
This recruits the lipid kinase PI 3-kinase.
19
Q
What is the signalling motif and protein recruited of DAP12?
A
Signalling motif: tyrosine X X Leucine/Isoleucine - YXXL/I.
This recruits a Syk family kinase.
20
Q
What is conserved signalling in Nk cells DAP12 associated receptors?
A
- Receptor activation.
- Recruitment of a Src family kinase to phosphorylate the ITAMs.
- This recruits a Syk family kinase.
21
Q
What is conserved signalling in Nk cells DAP10 associated receptors?
A
- Receptor activation.
- Recruitment of a Src family kinase to phosphorylate the ITAMs.
- This recruits PI 3-kinase.
22
Q
What are integrins?
A
- Adhesion receptors that are expressed on pretty much every cell type.
- They are important for sensing and transient adhesion to other cells or the RCM and communicating the mechanical functions needed in response to what is detected
- It plays a key role on connecting the cell exterior to the cytoskeleton.
- Not always active but needs to be turned on.
23
Q
What are the 2 main type of integrin receptors?
A
- ß1 integrins that are expressed on essentially every cell and communicate with the ECM.
- ß2 integrins that are mainly expressed on immune cells and important for interactions between them
24
Q
What is a secondary function of ß2 integrins?
A
- They are key markers of immune cells for identification.
- eg. aMß2 integrin is a key identifier of macrophages.
25
How are integrins on the cell surface when they are inactive?
1. They are expressed in a close conformation.
2. This means that no ligand can bind and no signal can be transmitted.
26
How are integrins activated to the open conformation?
1. Signalling from other receptors like chemokines or triggers signalling from inside the cell.
2. This causes the integrin to change conformation.
3. This open conformation and allows ligands to bind.
27
What is unique to integrins?
They need to be activated to be able to signal.
28
What are the key signals in T cells that can activate integrins?
1. Engagement of the TCR or co-receptors.
2. Chemokine receptor engagement that signals for migration or extravasation.
29
What is the result of a ligand binding to an integrin?
1. Actin rearrangements in the cytoskeleton.
2. This has function like migration.
30
What key role do integrins play in immune cells?
co stimulation
31
What is the TNF receptor family?
1. They are membrane-bound receptors with mostly membrane-bound ligands.
2. includes death receptors like Fas.
3. Includes lymphocyte differentiation and co stimulatory receptors.
4. They signal through TRAF adaptors that all have distinct signalling motifs.
5. The ligands for TNF receptors are trimers and activate the receptor by crosslinking the trimeric ligands.
32
Why is TNF unusal?
It is the only soluble ligand for the TNF receptor family.
33
What is TRAF?
TNF receptor-associated factor
34
How do TNF receptors act as co-stimulatory molecules for APCs?
1. When an APC is activated, it needs co-stimulation from T helper cells to function efficiently.
2. The T helper cells express CD40L which is a TNF receptor ligand.
3. The APC expressed CD40 which is a TNF receptor.
4. When CD40 is engaged, it allows co-stimulation of macrophages, B cells and dendritic cells. This aids their function.
35
What TNF receptors have potential for cancer treatment?
1. OX40
2. 4-1BB
36
What is the role of OX40 and 4-1BB?
They costimulate T cells and guide differentation.
37
How is 4-1BB used in cancer therapy?
1. anti-4-1BB antibodies haven't worked or have been too toxic.
2. A 4-1BB signalling motif is a key part of chimeric antigen receptors (CAR).
38
How does CAR T cell therapy work?
1. A chimeric antigen receptor (CAR) is made of an antibody Fv recognition domain and T cell signalling domain.
2. CAR signalling replaces the need for TCR signalling to activate T cells.
3. The extracellular antibody Fv chain is specific for whatever tumour cells you want to target. This can selectively target cancer cells.
4. CAR T-cell therapy often focuses on CD19 which is commonly expressed in lots of B cell lymphomas.
5. This Fv antibody chain is linked to a signalling domain that can activate the T cell.
39
How is the 4-1BB signalling motif used in CAR T-cell therapy?
1. 1st generation CAR T-cell therapy linked directly to the TCR and it wasn’t very effective.
2. 2nd generation CAR T-cell therapy uses costimulation.
3. It takes the zeta chain from the TCR for signalling.
4. Uses the 4-1BB TNR receptor motif to costimulate the siganlling and activate the T cells.
5. This makes long lived T cells specific to the cancer cells but they are not quite as cytotoxic as normally activated T cells.
40
What are cytokines?
Universal soluble mediators of immunity
41
How do cytokine receptor detect the vast numbers of different cyokines?
1. There are lots of different cytokines so lots of receptors that all follow a similar design.
2. The receptor contains a conserved signal transduction chain.
3. Signal transduction domains associate with receptor chains.
42
What are the 3 conserved signal transduction chain in cytokine receptors?
1. ß chain which forms part of IL3 and IL5.
2. GP130
3. Gamma chain which is the most common/relevant.
43
Why are the conserved domains of cytokines receptors important?
You can make many receptors with only changing part of it. This makes it more efficient.
44
Why is the y chain the most relevant in cytokine receptors?
Many of the T cell specific cytokines use gamma chains.
45
What makes up the IL-2 receptor?
1. Constitutive expression of the gamma chain.
2. Constitutive expression of the IL-2Rß chain.
3. Together these 2 don’t work very well.
4. When the T cell is activated the IL-2Ra chain is expression.
5. The T cell can begin responding to IL-2.
46
What is the signalling mechanism of cytokine receptors?
1. The binding of the cytokine causes a conformational change.
2. The tyrosine residues in the cytoplasmic domain can be autophosphorylated and recruit Janus-kinases.
47
Receptor family key components and molecules: TCR
Protein interaction motif: ITAMs
Downstream signalling molecules: Lck and ZAP70
48
Receptor family key components and molecules: BCR
Protein interaction motif: ITAM
Downstream signalling molecules: Lyn and Syk
49
Receptor family key components and molecules: CD28 family
Protein interaction motif: ITAM/ITIM/ITSM
Downstream signalling molecules: PI 3-kinase
50
Receptor family key components and molecules: FcR
Protein interaction motif: ITAM
Downstream signalling molecules: Src family and Syk
51
Receptor family key components and molecules: NK cell receptors
Protein interaction motif: DAP10 ITAM, DAP12 ITAM
Downstream signalling molecules: PI 3-kinase, Syk
52
Receptor family key components and molecules: Integrins
Downstream signalling molecules: cytoskeletal adaptors like talin
53
Receptor family key components and molecules: TNFR
Protein interaction motif: TRAF binding-motif
Downstream signalling molecules: TRAFs
54
Receptor family key components and molecules: Cytokines receptor family
Protein interaction motif: JAK binding motif
Downstream signalling molecules: JAK
