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UBC Microbiology 212 > Immunology Chapter 8 > Flashcards

Immunology Chapter 8 Flashcards

(73 cards)

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1
Q

Antigen Presentation is when

A

dendritic cells (and other apcs) display peptide fragments from pathogens on their surfaces

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2
Q

dendritic cells present these pathogen peptide fragments to

A

T cells

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3
Q

what proteins display these peptide fragments to T cells?

A

MHC I and MHC II proteins

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4
Q

where are MHC proteins found

A

surface of cells

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5
Q

function of MHC I and MHC II

A

allow dendritic cells to communicate with T cells that there is an infection in the body and needs the adaptive immune system

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6
Q

the cells display peptides in the

A

clefts of the MHC protein

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7
Q

these peptides can be derived from

A

healthy proteins (normal-self proteins)
infection (proteins from pathogens)

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8
Q

Both MHC I and II have peptide-binding grooves, what do they do?

A

hold short peptides for T cell recognition

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9
Q

MHC is polygenic, what does that mean?

A

several genes that encode proteins that have the same function

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10
Q

In humans, there are 3 different MHC I proteins, what are they?

A

HLA-A, HLA-B, HLA-C

they have very similar structure, but are not the same

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11
Q

In humans there are 3 different MHC II proteins, what are they?

A

HLA-DP, HLA-DR, HLA-DQ

they have very similar structure, but are not the same

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12
Q

Why are the 6 human MHC proteins similar in structure, but are not exactly the same?

A

gene duplication then divergence (mutation)

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13
Q

MHC is also polymorphic, what does that mean?

A

there are different alleles in the human population === different variants of the same gene

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14
Q

HLA proteins are co-dominantly expressed, what does that mean?

A

50% of MHC Class I expressed on each cell is from mom, and the other 50% is from dad

that means, your cells transcribe both alleles and make the protein products of both genes

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15
Q

How many variants of MHC Class I proteins do your cells have the ability to make?

A

6 different MHC I Class proteins

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16
Q

MHC Class I are expressed on

A

most nucleated cells (except rbc)

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17
Q

What is MHC Class I made of

A

transmembrane a chain

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18
Q

the transmembrane a chain of MHC class I is non-covalently associated with

A

β2-microglobulin

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19
Q

the peptide binding groove is located

A

within the a-chain

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20
Q

the peptide that binds to MHC I is about …. amino acids long

A

8-10

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21
Q

The ends of the peptide interact tightly with the MHC Class I molecule to…

A

anchor it in place

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22
Q

MHC Class II are only found on

A

antigen presenting cells

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23
Q

mention some examples of antigen presenting cells

A

B cells, macrophages, dendritic cells

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24
Q

what cells express both MHC Class I and II

A

thymic epithelial cells

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25
what are MHC II made of identical transmembrane proteins called...
a-chain and β-chain
26
The peptide binding groove for MHC II is
between the a-chain and β-chain
27
the peptide that binds to MHC II is about .... amino acids long
13 or more
28
Unlike class I, the ends of the peptide do not interact with MHC Class II molecule, why?
so the peptide can extend beyond the groove
29
Is every individual in a population able to respond to a particular pathogen?
No, because some individuals may not express MHC allele that can bind to peptides from that pathogen
30
Why is MHC so polymorphic
- allows cells to present as many different types of peptides as possible - protection against wide range of pathogens - prevent pathogens from invading the immune system - ensure survival of the species (not individual)
31
Cheetahs and Tasmanian devils are two animal species with limited MHC diversity. What happens if their MHC cannot bind to a pathogen peptide?
they will go extinct
32
What is the disadvantage of polymorphism
when patients need an organ donor it/s difficult to find a match of someone with the same versions of MHC molecule that's why transplants are more successful with family/relatives organ
33
What are the two diseases concerning organ transplant
host versus graft disease graft versus host disease
34
what is host versus graft disease
it's when the recipient's immune system attacks the transplanted graft
35
what is graft versus host disease
when transplanted graft's immune system attacks the recipient's immune system
36
MHC Class I displayes peptides from...
intracellular protein (in healthy uninfected cells) viral proteins
37
the proteins displayed by MHC Class I are made by
ribosomes in the cytoplasm
38
MHC Class II displays peptides from
extracellular proteins that are taken up by the cell via endocytosis into an endosome - virus, toxins, bacteria
39
What is antigen processing
degradation of proteins into peptide fragments
40
what is antigen presentation
binding of these peptides to MHC proteins and their display on the cell surface for recognition by T cells
41
There are 3 pathways of antigen processing, what are they?
Endogenous Pathways (MHC Class I) Exogenous Pathway (MHC Class II) Cross-Presentation Pathway
42
Explain the process of MHC I Presentation
intracellular proteins are broken down into peptides (with different lengths) by proteosome TAP uses ATP to move the peptides into ER peptides bind to newly formed (nascent) MHC Class I inside the ER MHC Class I-peptide complex is transported via Golgi Apparatus to the cell surface
43
What type of T cells recognize MHC Class I-peptide complex?
CD8+ T cells
44
How long is the MHC Class I-peptide complex displayed
24 hours
45
What type of antigens does the MHC Class II pathway process
extracellular antigens like bacteria, viruses, soluble proteins taken in by the cell
46
Where are MHC Class II proteins made
ER
47
What protein initially associates with MHC Class II in the ER and what is its function?
Invariant chain (Ii) which blocks the peptide-binding groove to prevent premature peptide binding.
48
What happens to the MHC Class II Invariant Chain complex after formation in the ER?
It is packaged into vesicles and exits the ER
49
The invariant chain is then partially digested, and it leaves a small protein called.... in the....
CLIP in the peptide binding site
50
How does the cell take up extracellular antigens
endocytosis / phagocytosis
51
What happens to the engulfed extracellular material in the cell
It fuses with a lysosome, and is degraded by proteases
52
Do degraded peptides from extracellular antigens enter the cytoplasm
No, they stay in the vesicle
53
MHC-II - Ii complex fuses with the peptide containing vesicles, then what is removed?
CLIP is removed, and replaced with a peptide
54
What is the final step in the MHC Class II antigen presentation pathway?
The MHC Class II - peptide complex is transported to the cell surface for recognition by CD4+ T cells
55
Dendritic cells can do cross-presentation, what is it?
a blend of both exogenous and endogenous pathways where MHC Class I presents exogenous, normally handled by MHC Class II
56
Which type of cells are primarily capable of cross-presentation?
Dendritic cells
57
Why is cross-presentation important for immune defense
so the immune system can activate CD8+ T cells against viruses that do not infect dendritic cells directly
58
Cross presentation starts with what pathway, and what does it do
exogenous pathway, where the virus particle is phagocytosed into cytoplasm and digested by proteases
59
After getting phagocytosed, the dendritic cells receive a signal to take two pathways, the path to MHC I and the path to MHC II, what is the event called, and what is it?
change over event --> some of the fragments are diverted to the proteosome in the cytoplasm
60
Some of the peptides processed by the proteosome are loaded into the TAP protein for MHC I, but some peptides are unprocessed, what happens to the unprocessed peptides?
they get loaded onto MHC II
61
Why is dual presentation (on both MHC I and II) beneficial?
It helps initiate strong and coordinated antiviral immune responses.
62
MHC Class I activates what type of T cells
CD8+ cytotoxic T cells
63
MHC Class II activates what type of T cells
CD4+ helper T cells
64
What is protein turnover
continuous process of breaking down old proteins and making new ones in eukaryotes
65
Why is protein turnover important?
ensures precise regulation of protein levels and allows the cells to respond to changes in its environment
66
Are MHC proteins subject to turnover?
Yes, they are continuously replaced, especially during infections
67
What happens to MHC proteins during a viral infection
Old MHC is replaced with new MHC to present viral peptides to T cells
68
Can all MHC proteins bind to the same peptides?
No, each binds some but not all peptides, this redundancy enhances immune protection
69
Dendritic cells constitutively express MHC Class I, MHC Class II and co-stimulatory molecule....
B7
70
Immature dendritic cells are very phagocytic, but once they have started expressing the MHC etc, they
mature very quickly and migrate to the lymph node to activate naive T cells
71
Why do dendritic cells have a lot of surface area
to simultaneously activate many naive T cells
72
Which would be a likely effect if the TAP proteins were not able to transport peptides into the lumen of the E.R
Decreased MHC Class I expression at the cell surface
73
Dendritic cells, macrophages and B cells are examples of cells that express MHC class II proteins. These cells are also known as antigen-presenting cells. Do these cells express MHC Class I?
No

UBC Microbiology 212 (23 decks)

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