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Host Defense Exam 1 > Antigen Presentation > Flashcards

Antigen Presentation Flashcards

1
Q

List the antigen presenting cells.

A

Mononuclear Phagocytes => macrophages
Dendritic Cells
B Cells

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2
Q

Where are mononuclear phagocytes/macrophages found?

A

blood, liver, spleen

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3
Q

Where are dendritic cells found?

A

skin, lymph tissue

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4
Q

Where are B Cells found?

A

lymph tissue, immune reaction sites

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5
Q

Which APCs are phagocytic?

A

macrophages

dendritic cells

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6
Q

What are Kupffer cells?

A

liver sinusoidal macrophages

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7
Q

What are microglial cells?

A

brain macrophages

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8
Q

What are Langerhans’ cells?

A

skin dendritic cells located between skin layers

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9
Q

Where are follicular dendritic cells found?

A

found in the B cell zone of lymph nodes

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10
Q

Where are interdigitating dendritic cells found?

A

found in the T cell zone of lymph nodes

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11
Q

Describe how Langerhans’ cells respond to antigen?

A
  • phagocytose antigen in the skin
  • travel to the lymph nodes via afferent lymphatic vessels
  • once they enter the part of the lymph node where T cells are present, they are interdigitating cells
  • interdigitate with T cells and present antigen
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12
Q

What happens to dendritic cells once they phagocytose the antigen?

A
  • increased MHC expression
  • increased surface area
  • decreased phagocytic capabilities
  • increased presentation capabilities
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13
Q

What are the 2 dendritic cell lineages?

A
  • conventional

- plasmacytoid - produce anti-viral interferons

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14
Q

Where is MHC synthesized?

A

ER

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15
Q

Describe the mechanism of antigen processing in Class I expressing cells.

A
  1. virus enters the cell => uncoats => hijacks nucleus => production of viral proteins
  2. viral proteins are degraded into peptides via the proteasome
  3. antigen peptides enter the ER through TAP transporter proteins
  4. ERAAP cleaves the peptides further into 8-10 AA that will fit in the MHC Class I peptide cleft
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16
Q

What are the domains of the proteasome?

A

LMP2

LMP7

17
Q

Describe MHC Class I maturation.

A
  1. nascent MHC Class 1 alpha chain is misfolded and associated with calnexin
  2. B2-m invariant chain then joins the misfolded alpha chain => dissociates from calnexin
  3. nascent MHC (alpha and beta) join chaperone proteins calreticulin and ERp57
  4. associates with tapasin, which brings it closer to TAP
  5. processed antigen enters through TAP and binds to MHC Class I
  6. released from ER in an endosome
  7. surface expression
18
Q

To what T cells to Class I molecules present?

A

CD8+ cytotoxic T cells

19
Q

What happens to Class I antigen processing and presentation under normal conditions?

A

old, defective, or misfolded proteins that are destined for the proteasome get degraded and are loaded on to MHC to act as self-antigens

20
Q

Describe antigen processing in MHC Class II expressing cells.

A
  1. foreign antigen is phagocytosed into a phagolysosome

2. phagolysosome is acidified and antigen is degraded into peptides

21
Q

Describe the mechanisms of MHC Class II maturation.

A
  1. fully synthesized MHC Class II is associated with an invariant chain the ER
  2. MHC:Invariant is released from the ER into an endosome
  3. The endosome is acidified and the invariant chain is degraded, except for CLIP that remains in the peptide cleft
22
Q

Describe the mechanism of antigen loading in MHC Class II expressing cells.

A
  1. phagolysosome carrying degraded antigen peptide fuses with the endosome carrying MHC:CLIP
  2. HLA-DM enters the fused vesicle and unload CLIP
  3. loads and unloads antigen peptides until one is bound tightly enough to resist unloading
  4. MHC:Peptide is expressed on the surface
23
Q

To what T cells do MHC Class II molecules present?

A

CD4+ T cells

24
Q

What do MHC Class II cells express under normal conditions?

A

CLIP

25
Q

Compare MHC maturation in Class I and Class II cells.

A

Class I: completed in the ER and then released

Class II: only MHC is released from the ER; loading occurs in the cytosol

26
Q

Compare MHC normal condition expression in Class I and Class II cells.

A

Class I = self antigen

Class II = CLIP

27
Q

Compare MHC antigen sources in Class I and Class II cels.

A

Class I = invader virus creates viral proteins inside the cell
Class II = foreign antigen found in the ECF is phagocytosed

28
Q

Define MHC restriction in T cell recognition.

A

CD4+ T cells will only recognize antigen if it is associated with MHC Class II on an APC

29
Q

What do TH1 cells do?

A

activate macrophages to kill the antigen that they phagocytosed

30
Q

What do TH2 cells do?

A

activate B cells to produce antibodies

31
Q

What are the signals needed for naive T cell activation?

A
  • MHC:peptide interacts with TCR

- B7 interacts with CD28

32
Q

What happens if T cells come in contact with APCs that do not express B7?

A
  1. MHC:Peptide interacts with TCR
  2. T cell expresses CD40L
  3. CD40L interacts with CD40 on APC surface
  4. CD40 binding stimulates APC to express B7
  5. B7 interacts with CD28 => second signal complete
33
Q

What signals are needed for T cells to activate B cell proliferation?

A
  • MHC:Peptide => TCR
  • B7 => CD28
  • CD40 => CD40L => cytokines released
34
Q

Describe the zones of the immune synapse.

A

central zone = MHC:peptides and co-stimulatory factors

peripheral zone = adhesion molecules (T cell expresses LFA, APC expresses ICAM)

35
Q

What is the purpose of adhesion molecules in the immune synapse?

A

allows for better interaction between MHC:peptide and TCR

Host Defense Exam 1 (12 decks)

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