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Immunology > B-Cell and T-Cell Receptor Diversity > Flashcards

B-Cell and T-Cell Receptor Diversity Flashcards

1
Q

Describe the structural properties of antibodies and explain how they relate to function.

A

Antibody: 4 Chain unit
-2 identical heavy chains
-2 identical light chains
-BIVALENT
Heavy and light chains are held together by INTERCHAIN Disulfide bonds
some antibodies are secreted forms, and membrane bound forms
Y-shaped structure with 2 arms (each arm binds an antigen)

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2
Q

Distinguish between Fab and Fc fragments

A

Fab- fragment antigen binding: 2 identical fragments that bind antigen
Fc- Fragment Crystallizable; 1 fragment responsible for destroying or clearing antigen from our bodies (effector functions)

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3
Q

Discuss how antibodies and antigens interact. How do antigen-binding sites differ?

A

antibodies and antigens react via NON-COVALENT forces.
-electrostatic force- attraction between opposite charges
-hydrogen bonds- hydrogen shared between electronegative atoms
-hydrophobic forces- clustering of hydrophobic groups in aqueous environment
Van der waals-
Antigen binding sites vary in SHAPE, and PHYSICAL PROPERTIES. (ex: Pocket, groove, surface, knob binding sites). each antigen-binding site include Variable heavy, V-light chain

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4
Q

What is an epitope?

A

eptiope- small region on antigen to which antibody binds to.
- epitope aka ANTIGENIC DETERMINANT- contains 7-15 amino acids.

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5
Q

Differentiate between affinity and avidity

A

Affinity- measures strength of interaction between 1 epitope and 1 antigen-binding site of an antibody (1 Fab and antibody)
avidity- sum of all individual affinities

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6
Q

What is cross-reactivity?

A

Cross-reactivity- occurs when antibody that is targeted for one specific antigen, successfully binds to another different antigen
-ex: tetanus shot, immunizations

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7
Q

Distinguish between linear and conformational epitopes

A

Linear epitopes- RETAIN linear aa sequence (whether folded or not)
conformational or discontinuous epitope- epitope that is broken down when molecule is denatured, conformational epitope lost (lose shape), aa sequence

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8
Q

List and describe each mechanism that contributes to the generation of antibody diversity.

A

a

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9
Q

Differentiate between the mechanisms that occur before encounter with antigen and those that occur After encounter with antigen

A

Before encounter with antigen: SOMATIC RECOMBINATION
After encounter with antigen:
-secreted antibodies
-somatic hypermutation/Affinity maturation
-Class switching

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10
Q

Explain how IgM and IgD of the same antigen specificity are produced in naive B cells.

A
  • when making IgM and IgD, heavy chains are made with hydrophobic sequence on carboxy terminus.
    1. These immunoglobulins enter ER and are bound to membrane of ER.
    2. These heavy and light chains of Igs associate with Ig-alpha and Ig-Beta transmembrane proteins to transport to cell surface
    3. there, complex of IgM, Ig-alpha, Ig- Beta is made and forms B-cell receptor.
    4. the long cytoplasmic tails of Ig-alpha and Ig-beta will signal to BCR that antigen has been bound to receptor.
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11
Q

Distinguish between P nucleotides and N nucleotides

A

P nucleotides- “PALINDROMIC”- consequence of RAG endonuclease action which creates DNA HAIRPINS. When repaired, the nick that opens the hairpin can occur at several positions leading to p nucleotides
N-Nucleotides- “NON-TEMPLATE”- consequence of Terminal deoxynucletoidyl Transferase (TdT). This enzyme ADDS NUCLEOTIDES to opened hairpin ends.

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12
Q

Compare and contrast the structure and function of the antibody isotypes

A

a

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13
Q

Define the term monoclonal antibody. Explain the evolution of monoclonal antibodies as therapeutic agents

A

a

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14
Q

What cells function in adaptive immune system? How is pathogen specificity acheived?

A

B and T lymphocytes carry out functions in Adaptive immune system.
Specificity for pathogens achieved through Antigen receptors on lymphocyte surface; ANTIBODY (BCR) and T-CELL receptor (TCR)
antigen= pathogen

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15
Q

how many different antigens can lymphocyte receptors bind to?
What kind of antigens do B cells respond to?

A

Lymphocyte receptors have unique structural features that enable it to bind to more than 10^( (billion, trillion) different antigens
B cells respond to extracellular antigens (macromolecules; proteins and carbohydrates)

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16
Q

What is the hinge-region in the antibody structure?

A

Hinge region- flexible stretch that allows antibody to bind with both arms to many different arrangements of antigens on the surface of pathogens (antigens in close proximity, and those far apart)

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17
Q

What molecule cleaves the antibody into functional distinct fragments?

A

PAPAIN- protease that will cleave y-shaped antibody into 1 Fc and 2 Fab fragments.

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18
Q

What forms Immunoglobulin domains? What are the two main regions of antibodies? What forms antigen binding sites?

A 
INTRACHAIN Disulfide bonds form immunoglobulin domains
Antibodies- proteins with variable and constant regions
AMINO termini (top) are variable in sequence and form Antigen binding sites
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19
Q

How many domains do immunoglobulin chains form and what are they composed of?
How many loops does light chain have vs heavy chain?

A

The immunoglobulin chains are folded into 12 compact, stable protein domains
each domain- composed of 2 Beta sheets connected by polypeptide loops.
Light chain- 2 loops (cystein residues, loop of 100 aa) 1 Variable and 1 constant
Heavy chain- 4 loops (1 variable, 3C)

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20
Q

What is antigen-binding site of antibody formed from?

A

antigen-binding site- formed from heavy and light VARIABLE domains.

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21
Q

What is the role of hypervariable region in antibodies?

Where are they located? What is another name for Hypervariable region?

A

Hypervariable- area where sequence variability is concentrated in 3 distinct regions of H and L variable regions
the hypervariable regions of antibody Variable domains lie in discrete loops at one end of domain structure
The antigen-binding site of an antibody is formed from hypervariable regions of Heavy and light-chain variable domains.
Hypervariable region also known as CDR (complementarity Determining Regions)

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22
Q

How many domains does 1 single antigen binding site contain? How does this relate to Fab fragment?

A

1 single antigen-binding site contains 6 Domains.

1 single Fab fragment- 6 CDRs or hypervariables.

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23
Q

What feature defines the main types of antibody classes? What do these antibody classes contain? What are the main types of antibody classes? what are the two different light chains?

A

Differences in HEAVY CHAIN CONSTANT regions define the 5 main types of antibody classes
each antibody class- functionally distinct
Antibody classes: IgG, IgM, IgD, IgA, and IgE
There are two light chains, Kappa (k) or lambda that have no functional differences (each antibody contains either 2 kappa or 2 lambda.

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24
Q

What is an antigen? Distinguish between multivalent and monovalent antibodies/ How does this relate to polyclonal antibodies and monoclonal antibodies?

A

Antigen- foreign substance that serves a target for antibodies
Monovalent antibody- antibody with affinity for only one epitope
Multivalent antibody- affinity for multiple epitopes (binding to multiple sites)
monoclonal antibodies- activate 1 antibody of 1 specificity ; 1 B cells
Polyclonal antibodies- antibodies secreted by many different B cells (different specificities)

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25
Q

What are the two types of mutlivalent antigens?

A

types of multivalent antigens:

  1. Multivalent with repeated epitope- -numerous copies of the same epitope, left and right Fab have identical specificity. ex: polysaccharide capsule
  2. Multivalent with Different epitope- protein antigen with different epitopes, using 1 Fab have; different specificities.
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26
Q

Describe the structure and function of IgM?

A

Structure:
IgM is a MONOMER on B cell (BCR, b-cell receptor)
-PENTAMER in serum (10 binding sites per antigen)
Function:
activate Complement, and Neutralization (inactivating pathogen/toxin)

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27
Q

What is the structure and function of IgA?

A 
2 subclasses of Ig A:
-IgA1- MONOMER in SERUM
-IgA2- dimer in secretions
functions:
-Neutralization
-Opsonization (enhance phagocytosis; Fc)
-Major form of immunity at MUCOSAL surfaces (eyes, lungs, saliva, breast milk)
-More IgA made than any other antibody
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28
Q

Describe the structure and function of IgG?

A

4 subclasses of IgG:
(these subclasses differ by structure of HINGE; Ig1,2,3,4)
Functions:
longest half-life- important for passive immunization (ex: monoclonal antibody for COVID)
-Neutralization
-Opsonization (coating pathogens with proteins to facilitate its destruction), enhance phagocytosis
-Complement activation
-CROSS PLACENTA (provide immunity to fetus)

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29
Q

What is the structure and function of IgD?

A

IgD

structure: monomer
function:
- BCR (b-cell receptor)
- binds to BASOPHILS via Fc region (in respiratory tract)

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30
Q

What is the structure and function of IgE?

A

IgE

structure: monomer
- LEAST abundant in serum- binds to MAST CELLS AND BASOPHILS via Fc region
- immunity against parasitic infections
- mediates allergic reactions

31
Q

What is junctional diversity? What are two main examples?

A

Junctional diversity- random incorporation of nucleotides at coding joints.
Junctional diversity - increases diversity in amino acid sequence of heavy and light chain CDR3s.
ex: P nucleotides and Nucleotides involved

32
Q

Describe the process of synthesizing secreted antibodies?

A

Process:

  1. IgM and IgD are first made in a membrane-bound form that is present on naive B cell surface- through BCR (b-cell receptor)
  2. Following B-cell activation, cells differentiate to become plasma cells.
  3. Plasma cells undergo ALTERNATIVE RNA SPLICING to produce secreted antibody.
33
Q

What are the roles of Ig-alpha and Ig-beta in secreting antibodies? How does the carboxy terminus differ in membrane bound vs when B cell activated?

A

Ig-alpha and Ig-Beta are important for SIGNAL TRANSDUCTION- they will give signal of B cell to be activated, start replication
- membrane bound carboxy terminus- hydrophobic region is anchored in membrane.
Once B cell activated, cell undergoes splicing to replace hydrophobic part with HYDROPHILLIC part at mRNA level.

34
Q

What occurs during Somatic Hypermutation and Affinity mutation?

A

Somatic hypermutation:
-Targeted introduction of POINT MUTATIONS into Variable regions of H and L chains
-leads to INCREASED antibody affinity
- process carried out by Activation-induced Cytidine Deaminase (AID) which deaminates Cytosine to Uracil
Affinity mutation follows after somatic hypermutation.
Affinity mutation- process of where a selection of antibodies have INCREASED AFFINITY for antigen.
most of these mutations arise in Variable region of CDR3 and also CDR1 (light)

35
Q

What role does point mutations play in variable regions?

A

Point mutations- change the strength of antibody binding to antigen (affinity); resulting in tighter affinity of antibody to antigen.

36
Q

What occurs during Isotype switching and components involved?

A

Isotype Switching:
-produces immunoglobulin with a DIFFERENT CONSTANT REGION (heavy) but identical antigen specificity.
-Antibodies with different constant regions have different effector functions.
- HOMOLOGOUS DNA recombination
-AID introduced point mutations in the SWITCH regions through nicks which facilitate recombination.
DNA is eventually lost an further switching to downstream isotypes (IgG) can take place

37
Q

Describe the steps of Isotype switching.

A

Isotype switching- mechanism changing a B cell’s production of one immunoglobulin to another immunoglobulin (change constant heavy region)
1. initially IgM and Ig D are produced on naive B cells-
2. AID selectively targets Su (mu) and S-gamma 1 switch regions
3, DNA in the S u and S-gamma switch regions are nicked on both strands
4. Looping out and switch region recombination occurs
5. DNA is excised out, and lost from genome, leading to IgG1 produced. (you cannot make IgM and IgD, since DNA is lost)
Su is switched to S-gamma region

38
Q

*Describe the structural properties of T-cell receptors and explain how they relate to function

A

T Cell receptors:

  • monovalent
  • membrane bound
  • Heterodimer: Alpha/beta receptor OR gamma/epilson receptor
  • Inter-chain disulfide bonds for heterodimer
  • Intrachain disulfide bonds for 2 Ig loop domains
  • 1 Variable and 1 Constant chain
  • 1 antigen binding site (Fb region)
  • cytoplasmic tails and membrane bound Fab chain
39
Q

*Discuss the mechanisms for how diversity is created in the TCR

A

T-cell receptor diversity generated by GENE REARRANGEMENT
1) Somatic recombination- occurs during T-cell development in THYMUS
-TCR chains made of 2-3 gene segments
Beta chain- like Antibody heavy chain- V-D-J
Alpha chain- like Antibody light- V-J
2) Junctional Diversity- P, N nucleotides
-NO receptor diversification after exposure to antigen.
-no secreted TCR, no somatic hypermutation, and no isotype switching.

40
Q
  • Explain how antibodies and TCRs(T-cell receptors) differ
A

-no isotype switching, no secretion of TCR or no somatic hypermutation in T-Cells; Antibodies have it.
- T-cells- cell mediated
TCR- monovalent; BCR- Bivalent
antibodies- 2 heavy, 2 light chains ; TCR- 1 V and 1 Constant chain
Antibodies- 2 antigen binding sites; TCR- 1 antigen binding site

41
Q

*Compare and Contrast CD4 and CD8 cells

A

Two types of T cells:
1. CD4- HELPER; recognize EXTRACELLULAR antigens and secrete CYTOKINES to activate MACROPHAGES and B-cells (drive differentiation into plasma cells- antibodies)
CD4 T cell recognize bacterial antigen presented by MHCII on macrophage and B cell.
2. CD8- CYTOTOXIC; recognize INTRACEULLULAR antigens and release toxic substances that kill infected cells
CD8- recognize viral antigens presented by MHC I on virus-infected cell

42
Q

*Describe the structure, distribution pattern, and function of MHC Class I and class II molecules

A 
Structure 
MHC I:
-3 alpha chain domains (anchored)
-1 Beta-2 microglobulin (NOT anchored)
-noncovalent association
-CD8+ T cells
MHC II
- 2 alpha chain domains
-2 Beta chain domains
-both chains are ANCHORED to membrane
-noncovalent association
CD4+ T cells
43
Q

*Distinguish between exogenous and endogenous including which class of MHC presents each type of antigen

A

pathogens present in 2 distinct cellular compartments
Endogenous- MHC I have intracellular proteins made in the cytosol and present VIRUSES in the cytosol and nucleus to CD9 cells.
Exogenous- MHC II have extracellular proteins made OUTSIDE of cell and present BACTERIA which are in VESICULAR region (ER, Golgi, endosomes, lysosomes) to CD4 cells.

44
Q

*Explain the mechanisms by which endogenous and exogenous antigens are processed.

A

a

45
Q

Discuss what is meant by genetic polymorphism of MHC proteins. Why is this important?

A

a

46
Q

What occurs during Somatic Recombination in B cells Before encounter with antigen?

A

Somatic Recombination: process where Immunoglobulin gene segments are cut and spliced.
Functional light chain gene: single recombination between VL and VJ segments (j- joining, V-variable)
Functional Heavy chain- 2 recombination events: 1. join DH and DJ segments together (D-diversity)
2. Combined DJ segments are joined to Variable region. VDJ segments combine to form exon.

47
Q

What chromosomes are the heavy chain, lambda light chain and kappa light chain?

A

Heavy chain- chromosome 14
Lamba (light chain)- Chromosome 22
Kappa (light chain)- chromosome 2

48
Q

What is the process of junctional diversity?

A

junctional diversity- contribution of P and N nucleotides to coding joints.
Steps:
1.RAG complex cleaves the heptamer RSSs from D and J gene segments to yield DNA hairpins
2. RAG complex opens hairpins by nicking one strand of DNA, generating Palindromic P nucleotides
3. N-Nucleotide additions by TdT (enzmye). These nucleotides are not encoded in germline
4. Single strands pair together
5. Unpaired nucleotides are removed by an exonuclease
6. Gaps are filled by DNA synthesis and ligation to form coding joint.

49
Q

Explain the different variable regions for light vs heavy chain and the components included.

A

Variable region in Light chain: 2 different segments, V and J (joining)
Variable region in Heavy chain: 3 different segments, V, D (diversity), and J
VDJ come together to provide increase diversity and variability.
Diversity is concentrated in CDR3 of heavy chain.

50
Q

What creates enormous diversity in the antigen binding sites of immunoglobulins?

A

RANDOM RECOMBINATION of gene segments- creates diversity.

51
Q

Describe the mechanism for Somatic Recombination.

A

Mechanism:
Each V, D, J gene segment is flanked by Recombination signal sequences (RSSs)
Each RSS contains heptamer and nonamer
-12/23 rule- says recombination can only occur between 2 spacers of different lengths, spacer 12 or spacer 23.
RAG Complex- RECOMBINASE (bound by heptamer/nonamer) composed of 2 RAG1 and 2 RAG-2 proteins, have ENDONUCLEASE Activity
process:
complex forms scaffold to bring in RSSs so they can be cleaved and spliced for recombination, creating two new DNA joints (1 nonfunctional signal joint and 1 coding joint)

52
Q

How do T cells recognize antigens? What do they recognize and how do they carry out effector functions?

A

T cells recognize antigens via their TCR (t-cell receptor)
- T-cells recognize SHORT PEPTIDE FRAGMENTS which arise from degradation of pathogens/antigens
T-cells recognize antigen and carry out their effector functions through CELL-to CELL CONTACT.

53
Q

What are some characteristics for the alpha/beta TCR vs gamma/epilson TCR?

A 
Alpha/beta TCR:
- major receptor in ADAPTIVE immunity
-MHC restriction
-Majority of T Cells
Gamma/Epsilon TCR:
-Not as well characterized
-Role in INNATE immunity
- NO MHC restriction
54
Q

Describe the hypervariable regions in TCRs. Where is the antigen-binding site of TCR formed?

A

In TCR:

  • sequence variability is concentrated in 3 discrete regions of alpha/beta chain variable domains
  • hypervariable regions of TCR Variable domains lie in discrete loops at one end of the domain structure 3 HVR= 3 CDRs
  • antigen binding site of TCR is formed from HYPERVARIABLE regions of Alpha/Beta Variable Domains.
55
Q

Describe the components of T-Cell Receptor Complex and Co-receptors and their related functions.

A

T- cell Receptor Complex:
-8 protein complex
-TCR- for ANTIGEN RECOGNITION (alpha/beta)
-CD3- contains 6 proteins
associates with TCR via electrostatic interactions;
invariant and used for SIGNAL TRANSDUCTION (gamma dimer).
CO-receptors: CD8 and Cd4 cells.

56
Q

What regions exhibit the highest amount of diversity between T-cell receptors?

A

Variable alpha and Variable-beta regions

57
Q

Describe how T cells recognize antigens.

A

T-cells recognize PROCESSED ANTIGEN (antigen fragments or epitope) that is presented on cell-surfaces by MHC proteins,
-a pathogen protein will appear in human cells
-antigen processing occurs (break down of pathogen protein)
- presentation of peptide by MHC molecule
recognition of antigen-MHC by T cell receptor

58
Q

What does MHC stand for? What are the two main classes and how do they differ?

A 
MHC- Major Histocompatibility Complex
2 classes: 
-MHC I
-MHC II
they differ in: 
-structure
-Cell distribution
-function- bind antigen from distinct cellular compartments
59
Q

Compare and contrast the shape of MHC folds for both MHC I and MHC II. What occurs in empty MHC molecule?

A

For MHC folds (both I and II):
common structure: alpha helix and beta sheets
-form deep groove which is PEPTIDE binding site
-non-covalent interactions
MHC I- is like PITA bread shape, with 8-10 amino acids
MHC II- is like HOT DOG shape, with 10-25 amino acids in groove
For EMPTY MHC molecule- there is PROMISCUOUS BINDING SPECIFICITY (each MHC bind to a rang of different peptide antigens)

60
Q

Describe MHC genetics. Where are genes encoded for MHC molecules? How would you describe MHC in terms of their genes?

A

The genes encoding MHC molecules are on chromosome 6, in area called HLA complex
HLA- Human Leukocyte Antigen
MHC are POLYGENIC- have class I gene family and class 2 gene family
-have multiple genes encoding MHC
MHC are also POLYMORPHIC- many allelic forms. Each class I and class II loci encode SIMILAR , but not identical proteins

61
Q

How is MHC POLYMORPHIC? How many loci for each MHC?

A

MHC are polymorphic- have many allelic forms.
each class I and class II loci encode similar but not identical proteins
MHC I- have 3 loci: B, C, A (alpha genes)
MHC II- have 3 loci: DP, DQ, DR (b/a)
alpha and beta chains derived from different class II loci DO NOT MIX

62
Q

Describe the type of inheritance in MHC genetics.

A

MHC inheritance is CO-DOMINANT:
-both maternal and paternal alleles are expressed.
-due to high polymorphism , it is likely that an individual will inherit DIFFERENT alleles from each parent.
HAPLOTYPE- particular combination of MHC alleles found in one chromosome.

63
Q

How many different MHC class I vs MHC II proteins are expressed on cell surface? Why does this occur and why is it important.

A

Due to polygenism, polymorphism, and Co-dominant expression:
-a human will express up to SIX different MHC I proteins and up to TWELVE different MHC II proteins on his or her cell surface.
This genetic variation ensures an individual will be able to bind and present a wide variety of antigens and have DIVERSITY.

64
Q

What is the benefit of Diversity or MHC?

A

Diversity is driven by NATURAL SELECTION; individuals with divergent haplotypes can respond against greatest number of pathogens
each haplotype contributes different binding specificities and Improves STRENGTH of IMMUNE response.

65
Q

Differentiate between the distribution of MHC I and II molecules.

A

Distribution:

  • all NUCLEATED cells express MHC class I
  • MHC class II ismainly expressed by professional antigen-presenting cells (APC):
  • DENDRITIC cells
  • MACROPHAGES
  • B-cells
  • also MICROGLIA and Activated-T cells have APCs.
66
Q

Compare and contrast the MHC I and II functions.

A 
MHC class I- interact with CD8 and present INTRACELLULAR antigen to CD8-T cells (conserved region alpha 3)
MHC class II- interact with CD4 and present EXTRACELLULAR antigen to CD4 T cells (Beta-2 conserved region)
67
Q

Describe antigen processing works in MHC I.

A

Antigen processing in MHC I:

1) Proteins are tagged with UBIQUITIN to form proteasome
- normal cell turnover- proteins are broken down into peptide fragments-both Self and Nonself (pathogen/antigen)
2) Peptides (> 8 aa) move from cytosol to ER
- carried out by TAP (Transporter associated with Antigen processing)
3) Peptide fragments are loaded onto MHC I

68
Q

compare and contrast constitutive proteasome from immunoproteosome in MHC I.

A

Constitutive proteosome- operates all the time, breaking down proteins (19 s cap)
Immunoproteosome (PA28 cap)- forms during INFECTION/ induced by Gamma-INTERFERON; producing peptides with HYDROPHOBIC or BASIC RESIDUES which favor binding to MHC I.

69
Q

What is the major role of TAP and what would be a consequence of a genetic defect in TAP?

A

TAP- moves peptides greater than 8 aa, from cytosol to ER.
defect in TAP: There would be no MHC I peptides. There would be a limited ability to respond to intracellular infections (viruses)
-no presenting of antigen to CD8 cells.

70
Q

What are the components of the peptide-loading complex for MHC I? What are the assembly and peptide loading stages for MHC I?

A

Peptide-loading complex:
formed from TAP, Tapasin, ERp527, Calreticulin, MHC I class heavy chain and B-2 microglobulin.
This complex helps peptide antigen bind to MHC I to be presented.
Assembly stage-
1. MHC I heavy chain stabilized by calnexin until B-2 microglobulin binds.
2. Calnexin is released, and peptide loading complex forms.
Peptide loading stage-
1. a peptide delivered by TAP binds to class I heavy chain forming mature MHC class I molecule
2. MHC I dissociates from peptide-binding complex and is exported from ER.

71
Q

What are strategies used to ensure effective peptide binding to MHC I? What is the role of TAPASIN in antigen processing with MHCI?

A

Strategies to ensure effective binding of peptide to MHC I:
PEPTIDE EDITING
1) TAPASIN
- brings MHC I in close proximity with TAP
-stabilized complex
-ensures that peptides bind with high affinity to MHC I
2) peptides that are too long are cleaved- ERAP

72
Q

Describe antigen processing and presentation for MHC II.

A

Antigen processing:

1) Extracellular Antigen taken into cell via PHAGOCYTOSIS (macrophages) or ENDOCYTOSIS
2) proteases in vesicle will break down proteins into peptides
3) MHC II delivered to endosome where they associate with peptide fragments
4) MHC II/peptide complexes move to cell surface

73
Q

Elaborate more on the antigen processing in MHC II. How are the vesicles activated to break down peptides? What is the role of invariant chain, CLIP and DM?

A
  1. once antigen is taken up from extracellular space into intracellular vesicles, vesicles have to be acidified
  2. after acidification of vesicles, proteases are activated to degrade antigen into peptide fragments
  3. vesicles containing peptides fuse with vesicles containing MHC class II (from Golgi)

Assembly to endosomes:
-alpha and Beta chains are assembled in the ER in association with INVARIANT CHAIN
- invariant chain prevents/blocks MHC class II from binding peptides in the ER
- in VESICLES, invariant chain is cleaved and CLIP fragment is formed. CLIP blocks binding of peptides to MHC class II in vesicles.
DM- chaperone protein that will release CLIP and allow peptide to bond to MHC II.

Immunology (11 decks)

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