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APO506 - MICROBIOLOGY & IMMUNOLOGY > WEEK 1: Antigen processing and presentation > Flashcards

WEEK 1: Antigen processing and presentation Flashcards

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Biology 101 flashcards
1
Q

antigen processing

A

the generation of MHC ligands

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2
Q

antigen presentation

A

the acquisition and presentation of MHC ligands

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3
Q

what does MHC stand for?

A

major histocompatabilty complex

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4
Q

what does HLA stand for? what is it?

A

human leukocyte antigen complex. human version of MHC found in many animals

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5
Q

what types of HLA are found in class |?

A

A, B and C

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6
Q

what types of molecules are found in class ||?

A

DQ, DR and DP

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7
Q

t cells and b cells recognise…

A

specific regions on pathogens

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8
Q

macrophages express receptors for…

A

many microbial constituents. eg, receptors TLR4 and CD14 recognise LPS which is on the cell wall of bacteria

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9
Q

explain the process of T cell recognition

A

antibodies binds to epitopes displayed on surface of antigen. antigen is then broken down into peptide fragments. this is then presented on MHC molecule. the MHC and peptide together are recognised by t cell receptor.

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10
Q

class | molecules are recognised by which cells?

A

CD8 killer T cells

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11
Q

class || molecules are recognised by which cells?

A

T helper cells

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12
Q

where are class | MHC expressed?

A

on all nucleated cells (not rbc’s)

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13
Q

what do T helper cells do?

A

produce cytokines, help B cells make antibodies or help Tc cells become effective killers

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14
Q

MHC molecules are highly polymorphic. what does this mean?

A

many different forms of these molecules

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15
Q

what is the class | structure composed of?

A

a single heavy polypeptide chain, domains (a for alpha) A1, A2, A3, a light polypeptide chain and a cytoplasmic tail.

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16
Q

what is the class ii structure composed of?

A

2 polypeptide chains, a and

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17
Q

where are polymorphisms concentrated in MHC class |?

A

alpha 1 and alpha 2 regions

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18
Q

why are polymorphisms beneficial?

A

greater variability, greater chance of presenting peptides from an invading pathogen that can be recognised by T cell.

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19
Q

in class || MHC, what is the antigen binding groove made up of?

A

alpha and beta chain

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20
Q

in class || MHC molecules, where are the most polymorphisms found?

A

tend to reside in beta 1 domain

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21
Q

where are class || MHC molecules found?

A

only on antigen presenting cells - they’re very restricted.

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22
Q

in a class | MHC molecule, how long is the peptide chain?

A

its short - 8-10 amino acids long

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23
Q

how does the MHC molecule hold the peptide?

A

by deep pockets, usually at amino acids 2 and 9 or 10. AKA anchor motifs of peptide

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24
Q

why are peptide chains longer and flatter in class || MHC molecules?

A

the antigen binding group is more open due to the alpha and beta chains

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25
Q

what position of the amino acid are the anchor/binding motifs of peptide found in MHC class | found?

A

2 and 9 or 10

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26
Q

what does HLA-G do?

A

HLA-G inhibits class of NK cells. protects the fetus from NK recognition

27
Q

what does HLA-G do?

A

HLA-G inhibits class of NK cells. protects the fetus from NK recognition

28
Q

what happens when NK cells recognise class | MHC molecules?

A

they’re inhibited.

29
Q

what happens when NK cells recognise the loss or altered versions of class | MHC molecules?

A

they release granules and kill that cell

30
Q

what do cytotoxic T cells express?

A

CD8

31
Q

what do T helper cells express?

A

CD4

32
Q

where are pathogens degraded?

A

in cytosol or endocytic vessels.

33
Q

if a pathogen is degraded in cytosol, which class of MHC does the peptide bind to?

A

MHC class |

34
Q

if a peptide binds to MHC class |, which T cell is it presented to?

A

effector CD8 T cell (naïve cell if pathogen is degraded by retro translocation)

35
Q

if a pathogen is degraded in endocytic vesicles, which MHC molecule does the peptide bind to?

A

MHC class ||

36
Q

if a peptide binds to MHC class ||, which T cell is it presented to?

A

effector CD4 T cell

37
Q

if a peptide binds to MHC class ||, which T cell is it presented to?

A

effector CD4 T cell

38
Q

how do macrophages take up antigens?

A

endocytosis and phagocytosis

39
Q

how do dendritic cells catch antigens? (epithelial cell)

A

use their long dendrites to catch antigen through epithelial cell

40
Q

what do follicular dendritic cells do?

A

they concentrate the antigen in beads. this enables B cells to acquire the antigen

41
Q

how are class i peptides derived?

A

via the secretory pathway- transported through the golgi apparatus then to the surface

42
Q

how are class ii peptides derived?

A

via receptor mediated phagocytosis in the endocytic pathway

43
Q

describe the structure of a class i molecule.

A

consists of a membrane bound heavy chain, beta 2 microglobulin and a peptide fragment

44
Q

what is calnexin? what does it do?

A

calnexin is a chaperone in stabilising the heavy chain and preventing aggrivation

45
Q

where do class i molecules fold and assemble?

A

in the endoplasmic reticulum (ER) lumen.

46
Q

what does ERp57 do? what is it?

A

it is a protein disulphide isomerase. it catalyses formation of disulphide bonds as part of the calnexin and calreticulin cycle.

47
Q

what does tapasin do? what is it?

A

its a specific class i accessory molecule and tethers molecules to the transporter. it also hols the structure together, folds TAP molecules and optimises peptide cargo to ensure a high affinity, stable complex.

48
Q

what is TAP?

A

the Transporter Associated with antigen Processing. it consists of TAP 1 and TAP 2, which both have one hydrophobic region and one ATP binding domain each.

49
Q

what is the role of TAP?

A

TAP is essential for peptide fragment delivery from the cytosol into the lumen of the ER, where these peptides are loaded on MHC molecules.

50
Q

how does TAP transport peptide fragments?

A

the peptide binding pocket is formed. the change in structure triggers ATP hydrolysis and initiates peptide transport.

51
Q

what does ERAAP stand for?

A

endoplasmic reticulum associated amino peptidase

52
Q

what does ERAP1 do?

A

it will trim the peptide if class i binds to a peptide that is too long before the molecule travels to the surface.

53
Q

what is tapasin?

A

a protein playing several roles in the stability and function of MHC complex

54
Q

what does tapasin do?

A

tapasin binds ERp57, serves as a bridge between class i molecules and TAP and promotes high affinity peptides. It also stabilises TAP transporter, increasing amount of peptides into ER lumen.

55
Q

what is the function of the invariant chain?

A

class ii binding groove binds to invariant chain which prevents class ii from binding with peptides meant for class i. it leads the class ii molecule out of ER and into golgi apparatus.

56
Q

where are MHC class i molecule peptides generated?

A

within the cytosol by the proteasome

57
Q

where are MHC class ii molecule peptides generated?

A

wthin endosomal/lysosomal pathway by a series of proteases

58
Q

how do pathogens evade antigen processing and presentation?

A

they change proteins that are targets for immune recognition, escape binding to the MHC and target the MHC class i and ii processing pathways.

59
Q

what does proteasome do?

A

breaks down cytosolic proteins (that will be used to create the peptide that will later be flagged as Tc cells recognise)

60
Q

describe the structure of proteasome

A

19s regulator and 20s is the core (which is made up of alpha and beta subunits). This forms 26s.

61
Q

describe the structure of immunoproteasome

A

composed of LMP2, LMP7 and MECL-1. This generates a proteasome required for peptide binding.

62
Q

what activates proteases to degrade antigen into peptide fragments?

A

a low pH. caused by pathogen

63
Q

how small are the bacteria’s endogenous fragments broken down into by the proteasome?

A

peptides that are about 15 amino acids in length

APO506 - MICROBIOLOGY & IMMUNOLOGY (10 decks)

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