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Immunology > Lec7 Cell Mediated Immune Response and Ag Processing > Flashcards

Lec7 Cell Mediated Immune Response and Ag Processing Flashcards

1
Q

T cell activation

A
  • by professional antigen presenting cells [pAPC] in lymph node
  • requires signal 1 and signal 2
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2
Q

CD4+ Cells

A
  • secrete cytokines, provide help to other immune cells
  • – secrete IFN-gamma: helps macrophages destroy pathogens
  • – secrete IL4 and IL5: help B cells make antibodies

suppress responses that could lead to autoimmunity or ongoing inflammation

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3
Q

CD8+ Cells

A
  • called CTLs
  • kill infected cells to clear infection
  • kill tumor cells
  • may also kill healthy cells in autoimmune response or during transplant rejection
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4
Q

What types of cells can be pAPC? What do they do?

A

pAPC are: macrophages, activated B cells, or dendritic cells [DCs]

  • process protein antigens into peptides and present them on surface with MHC
  • only cells that express class I and class II
  • only cells that produce both signals 1 and 2 required for naive T cell activation
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5
Q

What kind of cells can express class I and II MHC?

A

ONLY pAPC

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6
Q

What is unique about pAPC?

A
  • only cells that express both class I and class II MHC

- only cells that deliver both signals 1 and 2 that are required to activate naive T cells

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7
Q

What are the most effective pAPCs?

A

Dendritic Cells – activate T cells most efficiently because have lots of co-stimulatory molec

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8
Q

Three antigen processing pathways

A

Exogenous: antigen taken from outside cell, presented by class II to effector CD4 cell

Endogenous: antigen from inside cytosol [ie replicating virus], presented by class I to effector CD8 cell

Cross-presentation: infected cell/viral antigen picked up by pAPC exogenously and goes through exogenous path, but some viral protein leaks out of endosome into cytosol and processed by endogenous path, presented by class 1 to naive CD8

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9
Q

Which cells express class II MHC?

A

Only pAPCs

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10
Q

How are cytosolic pathogens processed?

A
  • Endogenous pathway
  • can occur in any cell
  • degraded protein in cytosol
  • displays MHC class I to effecor CD8
  • causes cell death
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11
Q

Describe the cross-presentation pathway of exogenous antigens?

A
  • occurs in pAPC, mostly in dendritic cell
  • pathogens start on exogenous path but then end up in cytosol where degraded
  • displays MHC class I to Naive CD8
  • can cause activation of CD8
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12
Q

Describe the exogenous pathway?

A
  • occurs in pAPCs [macrophages, B cells, etc]
  • pathogen degraded in endocytotic vesicle
  • displays MHC class II to effector CD4
  • activates macrophage killing of the bacteria or activates B cell to secrete Ig
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13
Q

What is the role of the adhesion molecule in Antigen recognition?

A

Adhesion molecule is non-specific, glues CD4 and pAPC together to allow for recognition

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14
Q

What are signal I and II?

A

Signal I: TCR binding MHC Class II

Signal II: costimulation signal

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15
Q

What are 2 main examples of signal II?

A

Signal 2 = Costimulation

  • CD28 on T cell binds B7 on pAPC
  • CD40 on pAPC binds CD40 Ligand [CDroL] on T cell
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16
Q

What is role of CD40?

A

It is a receptor on pAPC, binds CD40L on T cell and causes costimulation [signal 2]

17
Q

What is role of B7?

A

It is on the surface of pAPC

  • can bind CD28 for costimulation
  • can bind CTLA-4 for suppresion
18
Q

What is role of CD28?

A

It is a receptor on T cell, binds B7 on pAPC and causes costimulation [signal 2]

19
Q

What is role of CTLA-4?

A

It is a receptor on T cell, binds B7 and suppresses costimulation

20
Q

Describe signal I

A

T cell receptor binds MHC

MHC restriction: TCR sees self MHC and specific peptide

21
Q

Describe signal II pathway

A
  • happens in lymph node
  • signal 1 causes upregulation of CD40 ligand on T cell
  • CD40L binds CD40 increases expression of B7 and secretion cytokines
  • B7 binds CD28
22
Q

What is signal 3?

A
  • Cytokines are secreted following signal I and 2

- type of cytokines determines type of effector cells and response that takes place

23
Q

properties of cytokines

A
  • pleotropic: multiple actions
  • redundant: more than one cytokine has same function
  • produced transiently in small amounts
  • act locally [autocrine or paracrine]
  • can be toxic [cytokine storm] at high systemic level
24
Q

What determines specificity of TCR?

A

Alpha and beta chains

25
Q

What roles does CD3 complex play in T cell activation

A
  • CD3 complex responsible for activation signal after signal 1 and 2 received
  • also acts as cell surface marker of mature T cells
26
Q

What does Th1 cell secrete?

A
  • type of CD4

- secrete IL-2 and IFN-gamma

27
Q

Function of IL-2

A

induces T cell proliferation

28
Q

Function of IFN gamma

A
  • activates pAPC
  • promotes development effector response
  • helps B cells make complement fixing antibodies
29
Q

What does Th2 cell secrete?

A
  • type of CD4
  • secrete IL-4 and IL-5
  • involved in anti-parasitic response [helminths]
30
Q

Function of IL-4

A
  • Induces production IgE that mediate allergic response
31
Q

Function of IL-5

A
  • Activates eosinophils involved in allergic response
32
Q

What do Th17 cells secrete

A

IL-17

33
Q

Function of IL-17

A
  • Induce inflammatory responses by activating neutrophils

- Involved in mediating autoimmune disease

34
Q

What do T regulatory cells do? What do they secrete?

A
  • secrete TGFB and IL-10, suppressive cytokines

- Prevent autoimmune response and transplant rejection

35
Q

Natural T regulatory cells

A
  • CD4/CD25/FoxP3

- secrete Il-10 and TGF-B

36
Q

Tr1 cells - what do they secrete?

A
  • abundant in gut

- secrete IL-10

37
Q

Th3 cells - what do they secrete?

A
  • abundant in gut

- secrete TGF-B

38
Q

Central tolerance

A
  • immature self-reactive T cells undergo negative selection in thymus
39
Q

Peripheral tolerance

A
  • mature self-reactive T cells that escape central tolerance undergo anergy, deletion, regulation/suppression

Immunology (17 decks)

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