Antigen Uptake, Processing, and Presentation

Question 1

Antigens have to be ________ to be immunogenic

Answer 1

Processed (degraded)

Question 2

Experimental evidence that antigens have to be processed

Answer 2

1. Fixing cells (“freezes” proteins in naive conformation so they cannot process the Ag), fails to present
2. Fixing after the cell had the Ag permits presentation
3. Fixing the cell then exposing to Ag permits presentation.

Question 3

CD8 T cell recognises

Answer 3

Viral antigens presented by MHC I on virus-infected cells

Question 4

CD4 T cell recognises

Answer 4

Bacterial antigens presented by MHC II on macrophage
- Secretes cytokines to activate the macrophage and increase its killing capacity

Bacterial antigens presented by MHC II on B cells
- Secretes cytokines that drive differentiation of the B cell into plasma cell (antibody factories)

Question 5

Processing of exogenous antigens

Answer 5

endocytic vesicle fuses with lysosome - phagolysosome, peptide production that then displaces CLIP on MHC II.

Presented to CD4+ T cells.

Question 6

Processing of endogenous antigens

Answer 6

Processed in the proteasome then transported to the ER where it is loaded onto MHC I.

Presented to CD8+ T cells.

Question 7

Self-restriction of T cells

Answer 7

T cells only recognise antigen that is presented by the self-MHC molecule

Question 8

nearly all nucleated cells express MHC class ___

Answer 8

Class I, though at different levels, and can function as target cells.

low - fibroblasts, liver cells
none - neurons

Question 9

Antigen recognition by _____ T cells is restricted by ______ dictating whether a target cell is killed.

Answer 9

CD8+

Class I MHC

Question 10

How was it determined that CD8+ CTL is resctricted by class I MHC

Answer 10

1. H2k mice immunised with LCMV virus (t cell response)
2. T cells from mice spleen were challenged with LCMV-infected cells that were either H2k or H2b
3. Memory T cells could only kill H2k infected cells (matching MHC)
4. Thus, both the APC and target cell must have the same MHC.

Question 11

Steps in antigen loading

Answer 11

1. Calnexin stabilises the MHC I heavy chain until β2m binds
2. Calnexin released. peptide loading complex forms TAP, tapasin, ERp57, celreticulin, MHC I heavy chain and β2m.
3. Peptide is delivered by TAO, binds to the heavy chain and forms the mature MHC.
4. MHC I dissociates from peptide-loading complex, exported from the ER.

Question 12

Components of the MHC I peptide loading complex

Answer 12

TAP, tapasin, ERp57, calreticulin, MHC I heavy chain, β2m.

Question 13

Ubiquitination in the endogenous pathway

Answer 13

Ubiquitin binds cytoplasmic protein that are then targeted for proteolysis by the proteasome.

TAP then loads peptide fragments onto MHC I.

Question 14

TAP protein

Answer 14

Transporter Associated with Antigen Processing carries peptides from the cytoplasm into the RER using ATP

Has an affinity for 8-13 amino acid peptides and favours peptides with complementary amino acid positions to the anchor residues, loads peptides onto MHC I following proteolysis.

Question 15

Constitutive proteasome vs immunoproteasome

Answer 15

Constitutive - 19s cap
Immuno - PA28 cap

Immunoproteasome is better at creating peptides that can be loaded onto the MHC when in inflammatory conditions.

Question 16

ERAP

Answer 16

trims proteins that have been loaded onto the MHC I if they are too long.

Removes amino acids in sequence from the amino terminus

Question 17

Tapasin

Answer 17

When the MHC I binds a low-affinity peptide, tapasin binds, the α helix moves to widen the groove and the peptide is release.
Tapasin stabilises the empty MHC I so that it can bind a new high-affinity peptide, and groove narrowing forces release of tapasin.

Question 18

Process of MHC II loading

Answer 18

Antigen is endocytosied, early endosome is of neutral pH. Acidification activates proteases and the antigen is degraded into fragments. vesicles bind with other vesicles containing MHC II.

Question 19

MHC II in vesicles before binding the endosome

Answer 19

Invariant chain blocks binding of peptides in the ER.
In vesicles invariant chain is cleaved leaving the CLIP fragment bound, CLIP blocks peptide binding until DM facilitates release.

Question 20

T helper cells can only be activated by APCs with ______________

Answer 20

Self class MHC II alleles

Question 21

CD80/86

Answer 21

Costimulatory molecule that interacts with CD28 to boost CD4+ cell antigen recognition

Question 22

Costimulatory activity is the same in:

Answer 22

Dendritic cells, macrophages, and B cells.

Question 23

Exogenous pathway occurs in

Answer 23

Macrophages and dendritic cells use phagocytosis or endocytosis

B cells use endocytosis

Protease-containing vesicles with successively lower pH.

Question 24

MHC II are synthesised on ______ within the _____

Answer 24

polysomes; RER

associated with the invariant chain

Question 25

MHC II invariant chain

Answer 25

AKA CD74 Associates with new MHC II peptide-binding cleft to prevent bindin gof endogenous peptides, also ensures that the α/β chains fold properly, exit the RER< and route through the endocytic processing pathway.

Question 26

Degradation of the invariant chain

Answer 26

Occurs in the endocytic compartment and leaves a fragment termed CLIP, when the binding cleft assumes an open conformation, CLIP is replaced (catalysed by HLA-DM)

Question 27

HLA-DM and CLIP

Answer 27

HLA-DM is a nonclassical MHC II that catalyses the exchange of CLIP for an antigenic peptide.

Question 28

HLA-DO

Answer 28

A nonclassical MHC II that modulates the activity of HLA_DM, role in presentation of self-peptides and self-tolerance.

Question 29

Cross-presentation in dendritic cells

Answer 29

unique abilit to present exogenous antigens to CD8+ CTL. Activate CD$+ through class II which then license the DC to present exogenous Ags. This way dendritic cells can activate CTL even when not infected by virus. mediated by CD40L and CD40.

Question 30

IL-1 receptors

Answer 30

composed of two immunoglobulin chains that bind the IL-1 and transmit the signal via cytoplasmic TIR domains

Question 31

Inhibitory IL-1 ligands and receptors

Answer 31

IL-1Ra binds to IL-1RII, no cytoplasmic signalling. Or it binds sIL-1RII and sIL-1RAcP which are not membrane bound and act to sequester the cytokine.

Question 32

TNF receptor

Answer 32

Homotrimeric structure that must be formed to activate the death domains that initiate signal transduction. This then activates NFκB

Question 33

IL-1R receptor

Answer 33

Hematopoietin receptor consisting of α, β, γ polypeptides, affinity increases with more chains Signal transduction require the beta and gamma chains at the least.

Question 34

Low affinity IL-2R

Answer 34

Alpha chain only

Question 35

Intermediate affinity dimeric IL-2R

Answer 35

Beta and gamma chains

Question 36

High affinity trimeric IL-2R

Answer 36

Alpha beta and gamma chains

Question 37

Class two receptors structure

Answer 37

Require at least two polypeptides. The alpha chain associates with the cytokine then non-covalently with the signal transducing chains. Common gamma chain implies similar transmembrane signal even if other.

Question 38

Class I receptor competition

Answer 38

Different alpha subunits may compete for associating with limiting numbers of beta subunits in the plasma membrane May explain some antagonism

Question 39

Class 2 receptor reassortment

Answer 39

Multiple chains may reassort to bind atleast 27 different cytokines

Question 40

IL-17 receptors

Answer 40

May be dimeric, trimeric, homo- heter- di- or trimeric polypeptides.

Question 41

Chemokine receptors

Answer 41

All are GPCRs, composed of 7 transmembrane domains that cause the hydrolysis of a GDP, dissociation of α, βγ

Question 42

Soluble cytokine receptors and 4 functions

Answer 42

Forms in which they retain high affinity for the cytokine and can bind it in solution. 1. receptor down regulation 2. stabilises/protects the ligand from degradation 3. prevents binding to membrane-bound receptors (direct antagonist) 4. Confers sensitivity by binding the alpha chain

Question 43

How are soluble cytokine receptors produces

Answer 43

1. proteolytic cleavage of the extracellular domain - release from membrane, following an activation event on the cell (eg TNF, p55 and p75, are solubilised) 2. Splicing out the transmembrane encoding exon on the primary RNA transcript - IL-1RII, IL-4R, IL-7R

Question 44

Overview of cytokine receptor signalling

Answer 44

Achieved by the phosphorylation of proteins already present in the cytoplasm which results in a rapid pattern of alterations of many proteins.

Question 45

What kind of protein kinases are cytokine receptors

Answer 45

Tyrosine and serine/threonine

Question 46

Which cytokine receptor lack an intrinsic tyrosine kinase domain

Answer 46

Class I and Class II

Question 47

Janus Kinase

Answer 47

JAK Protein tyrosine kinases that are associated with the alpha chains of the receptor, only active in the presence of a ligand.

Question 48

Induction of receptor transduction in cytokine receptors

Answer 48

Binding of the cytokine to the receptor induces the dimerisation of two seperate cytokine receptor subunits, and JAK transphosphorylation that activates them. Activated JAKs create docking sites for the STATs by phosphorylation of specific tyrosine residues on the receptors. JAK then phosphorylates and activates STAT.

Question 49

STAT

Answer 49

Signal Transducers and Activators of Transcription, transcription factors. STAT SH2 domain docks the phosphorylated tyrosine on the cytokine receptor

Question 50

SH2 domain

Answer 50

On the STAT, allows for the docking to the phosphorylated tyrosine on the receptor

Question 51

Function of cytokine signalling following STAT phosphorylation

Answer 51

Phosphorylated STATs lose affinity for the receptor and translocate as a dimer to the nucleus for gene transcription. Genes that are transcribed are determined by the DNA sequence to which the STAT binds in the promoter region of a gene.

Question 52

Specificity of response in cytokine receptor transduction and resulting genes is determined by:

Answer 52

The many JAKs and STATs acting in different permutations

Question 53

TH cell cross-regulation at the level of intracellular signalling

Answer 53

Expression of the transcription factor T-Bet drives the cell to TH1 and away from TH2 by up regulating IFN-γ and suppressing IL-4 and IL-5. GATA-3 promotes the opposite and suppresses T-Bet function.

Question 54

Simultaneous activation of different cytokine receptors

Answer 54

Results in heterodimerisation of STATs as there are different phosphorylated STATs present.

Question 55

How are STAT1/STAT3 heterodimers produced

Answer 55

Simultaneous activation of different cytokine receptors by IL-6 (STAT) and IFN-γ (STAT1) on the same cell.

Question 56

Specificity of cytokine effect is due to three factors

Answer 56

1. the particular JAK/STAT pathway 2. STAT specific sequences in the promoter region of genes 3. only certain target genes can bye activated in different cell types, only a subset of the potential genes of a particular STAT may be permitted expression.

Question 57

Targeting STAT3 in cancer immunotherapy

Answer 57

STAT3 is hyperactivated in tumor ecosystem cells and inhibits the expression of crucial immune activation regulators, promotes the expression of immunosuppressive factors.

Question 58

What are JAK inhibitors used to treat

Answer 58

Rheumatoid arthritis and IBD.

Question 59

Chemokines and Ras

Answer 59

Leads to MAPK cascade and AP-1 gene expression

Question 60

Chemokine receptors and Rho

Answer 60

Activation leads to cell movement

Question 61

Chemokine receptors and PLCβ

Answer 61

Leads to NF-κB and new gene expression

Question 62

Chemokine receptors and JAKs

Answer 62

Lead to PKC activation to promote cell survival through Akt.

Question 63

Mechanism of IL-1, TNF, and IL-17 signal transduction

Answer 63

Serial phosphorylation of many proteins that leads to the activation of NF-κB

Question 64

NF-κB activation related to IκB

Answer 64

ΙκB inhibits NF-κB, phosphorylation induces ubiquitination and then proteasome degradation. NF-κΒ is then able to enter the nucleus and induce gene transcription.