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MICB 202 > Antigen-Presenting Cells and T Cell Activation > Flashcards

Antigen-Presenting Cells and T Cell Activation Flashcards

1
Q

What is the liaison between the innate and adaptive immune responses?

A

Dendritic cells

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2
Q

Where are dendritic cells found?

A

In all parts of the body that the immune system patrols

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3
Q

What is the role of dendritic cells?

A

To engulf (phagocytose) and break up (process) pathogens and to transport the pathogen’s remains to the local lymph node.

There, the dendritic cell presents peptides derived from the pathogen necessary for the activation of T cells.

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4
Q

What are Langerhans cells?

A

In the skin, immature dendritic cells are known as Langerhans cells.

They can efficiently phagocytose antigens but they cannot activate T cells until they migrate to the lymph node and become mature.

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5
Q

Dendritic cells express the same pattern recognition receptors as macrophages.

True or false?

A

True

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6
Q

What do the pattern recognition receptors on dendritic cells induce when activated?

A

They induce the dendritic cells to mature and migrate from the tissue to the local lymph node to present peptides derived from the pathogen to T cells.

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7
Q

Which MHC proteins do dendritic cells express?

A

Both MHC class I proteins and MHC class II proteins.

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8
Q

By the time dendritic cells reach the lymph node what do they express?

A

During the maturation process, dendritic cells up-regulate MHC class I and MHC class II production so that by the time they reach the lymph node they express very high levels of both proteins and are ready to present antigen as soon as they encounter the right T cell.

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9
Q

How do dendritic cells give a ‘snapshot’ of what is happening at the site of infection to the naïve T cells in the lymph nodes to initiate the adaptive response?

A

When engaged, the PRRs induce the dendritic cells to up-regulate the expression of other surface proteins (e.g., co-stimulatory proteins) to promote interactions with T cells that result in the activation of the T cell.

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10
Q

Which cells are able to present antigenic peptides complexed with MHC proteins?

A

Only professional antigen-presenting cells such as dendritic cells are able to present antigenic peptides complexed with MHC proteins and provide the co-stimulatory signal necessary to completely activate naïve T cells .

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11
Q

What is B7?

A

B7 is a set of cell-surface proteins on the antigen-presenting cell that binds to the CD28 protein on the T cell to provide to co-stimulatory signal.

The B7 proteins are also known as CD80 and CD86. APCs differ in their expression of the B7 proteins.

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12
Q

Name the two B7 proteins.

A

CD80 and CD86.

APCs differ in their expression of the B7 proteins.

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13
Q

Are immature dendritic cells phagocytic?

A

Immature dendritic cells are highly phagocytic but do not express homing receptors to lymph nodes or other peripheral lymphoid organs.

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14
Q

How does a dendritic cell mature?

A

Upon phagocytosis of a pathogen and subsequent interaction of the PRRs with PAMPs, the dendritic cell matures, expresses the homing receptors, and migrates (homes) to lymph nodes or other peripheral lymphoid organs.

Mature dendritic cells express very high levels of MHC and B7 proteins and are very powerful activators of T cells (but are no longer phagocytic).

Dendritic cells are the most potent activators of naïve T cells.

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15
Q

Which proteins do mature dendritic cells express very high levels?

A

MHC and B7 proteins and are very powerful activators of T cells (but are no longer phagocytic).

Dendritic cells are the most potent activators of naïve T cells.

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16
Q

What type of cells are the most potent activators of naïve T cells?

A

Mature dendritic cells

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17
Q

Why can’t resting macrophages activate naïve T cells?

A

Express low levels of MHC class II proteins and do not express B7 proteins

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18
Q

How may a macrophage become an activator of T cells?

A

When a macrophage is stimulated by the phagocytosis of an antigen (and subsequent interaction of the TLRs with the PAMPs), it increases its expression of both MHC class II and B7 proteins, and may become an activator of T cells.

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19
Q

What activates a B cell?

A

Resting B cells express low levels of MHC class II proteins but do not express B7 proteins.

The binding of antigen to the B cell receptor activates a B cell.

The B cell increases its expression of MHC class II proteins and begins to express B7 proteins.

B cells will also up-regulate expression of B7 if its TLRs interact with PAMPs.

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20
Q

If its TLRs interact with PAMPs how will B cells respond?

A

Up-regulate expression of B7

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21
Q

What two populations are T cells subdivided into?

A

T cells that express CD4 have TCRs that recognise antigenic peptides that are presented by MHC class II proteins.

CD4 T cells function as T helper cells.

T cells that express CD8 have TCRs that recognise antigenic peptides that are presented by MHC class I proteins.

CD8 T cells function as cytotoxic cells (CTLs).

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22
Q

What do CD4 T cells function as?

A

T helper cells

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23
Q

What do CD8 T cells function as?

A

cytotoxic cells (CTLs).

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24
Q

T cells that express CD4 have TCRs that recognise antigenic peptides that are presented by […]?

A

MHC class II proteins.

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25
Q

T cells that express CD8 have TCRs that recognise antigenic peptides that are presented by […]?

A

MHC class I proteins

26
Q

Full activation of a naïve T cell requires at least three signals.

What is the first signal?

What provides this signal?

A

The first signal is the interaction of the T cell’s TCR with the MHC + peptide complex on the antigen-presenting cell.

The binding of the co-receptor CD4 or CD8 to a conserved region of the MHC protein presenting the peptide strengthens this interaction (CD4 and CD8 proteins do not influence the antigen specificity of the TCR).

The CD3 complex then signals to the nucleus that the TCR has recognised the MHC-peptide complex of the antigen-presenting cell.

27
Q

CD4 and CD8 proteins influence the antigen specificity of the TCR.

True or false?

A

False

28
Q

What signals to the nucleus that the TCR has recognised the MHC-peptide complex of the antigen-presenting cell?

A

The CD3 complex

29
Q

Full activation of a naïve T cell requires at least three signals.

What is the second signal?

What provides this signal?

A

The second signal involves the interaction of an accessory protein, CD28, on the T cell with a co-stimulatory protein, B7, on the antigen-presenting cell.

30
Q

Full activation of a naïve T cell requires at least three signals.

What is the third signal?

What provides this signal?

A

The third signal involves cytokine signaling.

The cytokines can be secreted by both the antigen-presenting cell and the T cell itself.

31
Q

Once activated, what does the T cell need before it can proliferate?

A

The cytokine IL-2

T helper cells make enough of their own IL-2 to proliferate, whereas CTLs make some IL-2 but not enough, and depend on IL-2 made by T helper cells.

The antigen-presenting cell provides different cytokines to differentiation of the T cell into an effector T cell.

32
Q

Which cells provide the necessary co-stimulatory function to activate naïve T cells?

A

Only professional antigen-presenting cells can provide the necessary co-stimulatory function (i.e., expression of B7) to activate naïve T cells.

If a T cell receives only the antigen signal - for example, from an endothelial cell - and fails to receive the co-stimulatory signal (this is often called “signal 1 without signal 2”), the T cell enters a state of non-responsiveness known as clonal anergy.

33
Q

What is the role of the T helper cell in the adaptive immune response?

A

A CD4 T cell are T helper cells (or T regulatory cells) and recognise antigenic peptides presented by MHC class II proteins.

They provide “help” to other cells.

34
Q

Describe how a T helper cell helps other cells.

A

Help is often provided in the form of cytokines.

T helper cells may also “help” by providing activation interactions involving the CD40 ligand (CD40L), which is an important surface molecule for the activation of B cells, and can also enhance dendritic cell activation.

35
Q

What are cytokines?

A

Cytokines are proteins secreted by cells of the immune system used to direct the behavior of other immune cells.

36
Q

A CD4 T helper cell (after being activated by a professional antigen-preseting cell) provides help to what other cells?

How does it help each of these cell types?

A
  • antigen-activated B cells, so that they can proliferate and differentiate into antibody secreting plasma cells,
  • macrophages that have an intracellular bacterial infection, to increase the ability of the macrophage to kill the bacteria,
  • cytotoxic T cells (CTLs), to enhance their proliferation and differentiate into effector CTLs that can kill virus-infected cells.
37
Q

What do activated CD8 T cells develop into?

A

Cytotoxic T cells (CTLs) that are important for the recognition and elimination of cells infected with viruses, and also some tumors.

They are also involved in rejection of transplanted tissues. CD8 T cell recognise antigenic peptides presented by MHC class I proteins.

A naïve CD8 T cell is incapable of killing target cells. Full activation and proliferation of CTLs also requires sufficient concentration of IL-2, some of which is provided by T helper cells.

38
Q

What type of protein presents the antigenic peptides recognised by CD8 T cells?

A

MHC class I proteins.

39
Q

What do CTLs require in sufficient concentration for full activation and proliferation?

A

Full activation and proliferation of CTLs also requires sufficient concentration of IL-2, some of which is provided by T helper cells.

A naïve CD8 T cell is incapable of killing target cells.

40
Q

Briefly list the three signals required for T cell activation.

A

TCR ligation with MHC-peptide complex, and co-stimulation (B7, CD28) and cytokine signaling.

For proliferation and differentiation, IL-2 is also required.

41
Q

What are CTLs?

A

CTLs are killer T cells; they express CD8 and recognise MHC class I.

42
Q

What are T helper cells?

A

T helper cells help others immune cells, express CD4, and recognise MHC class II.

43
Q

T helper cells can be activated when an antigen-presenting cell presents the specific peptide on MHC class II.

True or false?

A

True

44
Q

Cytotoxic T cells express the CD8 protein as a co-receptor.

True or false?

A

True.

45
Q

The peptide bound to MHC class II proteins is usually derived from exogenous proteins.

True or false?

A

True

46
Q

MHC class II proteins present peptides to CD8 T cells.

True or false?

A

False.

47
Q

MHC class I can bind peptides derived from self and pathogen proteins.

True or false?

A

True

48
Q

The peptide bound to MHC class I protein is usually derived from exogenous proteins.

True or false?

A

False.

49
Q

MHC class I protein present peptides to CD8 T cells.

True or false?

A

True.

50
Q

The binding of B7 on the antigen-presenting cell to the CD28 protein on the T cell provides the co-stimulatory signal.

True or false?

A

True

51
Q

Even if a naïve T cell does not receive the co-stimulatory signal from a professional antigen presenting cell, it will still be activated.

True or false?

A

False.

52
Q

All cells of the body express the B7 protein; therefore any cell in the body can activate a naïve T cell.

True or false?

A

False

53
Q

Dendritic cells are the most potent activator of naïve T cells.

True or false?

A

True

54
Q

B cells will upregulate the expression of B7 once they have been activated by antigen.

True or false?

A

True.

55
Q

Cortical thymic epithelial cells also express MHC class II proteins; thus these cells would activate T helper cells as efficiently as a dendritic cell.

True or false?

A

False.

56
Q

Macrophages, dendritic cells and B cells are generally considered to be “professional” antigen presenting cells.

True or false?

A

True

57
Q

Activation of naïve T cells requires at least two signals; binding of the TCR to MHC-peptide on the antigen presenting cell and cytokines provided by the antigen presenting cell.

True or false?

A

False

58
Q

Interleukin-2 (IL-2) is a cytokine that promotes the proliferation of T cells.

True or false?

A

True

59
Q

CD28 signalling is required for the transcription of the IL-2 genes in T cells that have recognized MHC-peptide presented by an antigen presenting cell.

True or false?

A

True.

60
Q

CD4 cells are generally T helper cells and are activated when a dendritic cell presents peptide on a MHC class I molecule.

True or false?

A

False

MICB 202 (25 decks)

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