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Host Defense > Lecture 7: Antigen Presentation and the MHC > Flashcards

Lecture 7: Antigen Presentation and the MHC Flashcards

1
Q

All nucleated cells express ______ ______ __ molecules and can present antigen via these molecues

A

MHC Class I

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2
Q

What are 2 methods in which antigen presenting cells can take up antigen?

A

1) surface receptors

2) phagocytosis

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3
Q

What are the 3 cell types where MHC Class II is expressed?

A

1) Macrophages
2) Dendritic cells
3) B lymphocytes

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4
Q

What are skin APCs called? Where do they present antigen?

A

Langerhan cells; T cells

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5
Q

What are the 2 lineages of Dendritic Cells?

A

1) Conventional

2) Plasmacytoid

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6
Q

What is the function of Plasmacytoid cells?

A

produce large quantities of interferon in response to viral infections

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7
Q

What are the macrophages in the brain?

A

microglial

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8
Q

True or false: B lymphocytes present only one type of antigen?

A

True (whatever binds to B cell receptor)

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9
Q

What is required for the actual presentation of antigens for MHC Class I?

A

cytosolic production of viral proteins

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10
Q

How do MHC Class II molecules pick up the ingested antigen?

A

vesicles containing MHC Class II fuse with the vesicle in which the antigen was phagocytosed

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11
Q

Antigenic peptides that bind to MHC Class I are typically derived from ________

A

viruses

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12
Q

In MHC Class I antigen presentation, peptides generated in the cytoplasm are transported into the ER by ________ and ________.

A

TAP 1 and TAP 2

transporters associated with antigen processing

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13
Q

Once in the ER, how does the antigenic peptide associate with MHC Class I molecules?

A

MHC Class I associates with TAP and as peptides are transported into the ER, they are trimmed by ERAAP (endoplasmic reticulum aminopeptidase associated with antigen processing) then bind to MHC Class I

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14
Q

As MHC Class I is being made in the ER, what do the alpha chains post up against while waiting for the beta 2 microglobulin to bind?

A

calnexin

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15
Q

Once the beta 2 chains associate with the alpha chains of the MHC, what keeps the molecule from unfolding?

A

binding to chaperone protiens (calreticulin, ERp57)

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16
Q

Which chaperone facilitates MHC Class I binding to TAP?

A

tapasin

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17
Q

When is the MHC Class I molecule released to the membrane?

A

Once it has bound to its peptide in the ER (after ERAAP cleaved the incoming antigen)

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18
Q

MHC Class I peptides are degraded in the ____________ while MHC Class II molecules are degraded in _____________.

A

cytosol (by the proteasome) and acidified endosomes

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19
Q

MHC Class II molecules are transported to endosomes with _____________ which occupies the peptide binding cleft of the newly synthesized MHC

A

invariant chain (Ii)

20
Q

Once in the endosome, Ii is cleaved, leaving a short peptide fragment called _______

A

CLIP

class II associated invariant chain peptide

21
Q

CLIP is only removed from the binding cleft when the endosome fuses with an phagocytized vesicle of antigen. Which protein unloads CLIP and loads the antigen?

A

DM

22
Q

Under normal conditions, MHC Class I molecules are __________(loaded/unloaded) while MHC Class II are ___________

A

loaded (with self peptides derived from normal degradation)

unloaded (only have CLIP in binding groove)

23
Q

Under normal conditions, MHC Class I molecules are __________(loaded/unloaded) while MHC Class II are ___________

A

loaded (with self peptides derived from normal degradation)

unloaded (only have CLIP in binding groove)

24
Q

CD4 T lymphocytes do not recognize free/soluble antigens, they only recognize ________

A

MHC Class II bound

25
Q

What is MHC restriction?

A

the genetic restriction by class II molecule on which the antigenic determinant was first recognized

26
Q

What are the 2 potential functions of CD4 cells?

A

1) mediate macrophage activation

2) act as helper cells in antibody responses (secrete cytokines)

27
Q

What are the subset of CD4 T cells that activate macrophages?

A

Th1

28
Q

What are the subset of CD4 cells that induce antibody synthesis?

A

Th2 (helpers)

29
Q

What is the definition of naive T cells?

A

have never encountered antigen before

30
Q

Dendritic cells mature when they

A

phagocytize an antigen

31
Q

What feature of mature dendritic cells enhance their ability to present antigen?

A

expression on their surface of large amounts of co-stimulatory molecules (B7) and ability to express lots of cytokines for T cell differentiation and proliferation

32
Q

What are the 2 signals required for activation of naive T cell?

A

1) presentation of peptides by MHC (engages with TCR on T cell)
2) interaction between B7 on the APC and CD28 on membrane of the T cell

33
Q

B7 on the APC interacts with ______ on the T cell

A

CD28

34
Q

True or False: all APCs express B7

A

False

in this case, T cell activation relies on CD40

35
Q

All T cells that recognize peptides expressed by MHC Class II are stimulated to express _______

A

CD40L

CD40 ligand

36
Q

CD40L on the T cell engages ______ on the surface of the APC in order to induce expression of B7

A

CD40

37
Q

B7 binding to CD28 results in _________________

A

enhanced T cell proliferation and differentiation

38
Q

What process activates B cells to express B7?

A

displaying process peptides on surface MHC Class II

39
Q

After B7 of the B cell binds to CD28 on the T cell, what happens?

A

The T cell is stimulated to express CD40L which then engages CD40 on the surface of the B cell

40
Q

Once CD40L engages CD40, what happens?

A

the T cell is activated and produces cytokines and the B cell is free to proliferate and differentiate into plasma cells

41
Q

Define immunological synapse?

A

sustained TCR engagement and signaling with MHC peptides

42
Q

The activation of T cells is mediated by what 2 events

A

1) interaction of TCRs with their MHC ligands

2) B7 associating with CD28

43
Q

Ephemeral TCR engagement is sufficient for triggering killer T cells but __ _____ ____________ requires TCR engagement/signaling for many minutes or hours

A

T cell proliferation

44
Q

The mature immunological synapse is defined by a pattern of receptor segregation with a central cluster of TCRs surrounded by rind of adhesion molecules like ________

A

LFA-1

45
Q

The mature immunological synapse is defined by a pattern of receptor segregation with a central cluster of TCRs surrounded by ring of adhesion molecules like ________

A

LFA-1

46
Q

What is the purpose of the ring of adhesion molecules?

A

promote TCR-MHC-peptide interaction

47
Q

LFA-1 is on the _______ while ICAM is on the ______

A

T cell; APC

Host Defense (21 decks)

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