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IIH > B and T Cell Cooperation > Flashcards

B and T Cell Cooperation Flashcards

1
Q

Why do primary adaptive responses develop slowly?

A

Because naive T and B cells that recognise a new foreign antigen are few in number.

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2
Q

Which component of an antibody determines its effector function?

A

The type of heavy chain used.

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3
Q

Which phase precedes the response to a new foreign antigen in a primary response?

A

The lag phase.

*This is absent in a secondary response.

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4
Q

List 4 differences between a primary response and a secondary response.

A

1 - The frequency of antigen-specific B cells is greater in the secondary response.

2 - The isotype of antibody produced changes from IgM and IgG (where IgM is more frequent) in the primary response to IgA and IgG in the secondary response.

3 - The affinity of the antibody produced is higher in the secondary response.

4 - More antibodies show somatic hypermutation in the secondary response.

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5
Q

Define somatic hypermutation.

A

A cellular mechanism by which a B cell adapts its antibody production to foreign antigens.

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6
Q

What is a T independent antigen?

A

An antigen that causes antibody production by B cells without T cell involvement.

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7
Q

How does antibody production in the primary and secondary response differ in response to T independent antigens when compared to T dependent antigens?

A
  • In both the primary and secondary response to T independent antigens, there is high antibody production which comes about quickly.
  • In the primary response to T dependent antigens, there is a lag phase, followed by a moderate antibody production which comes about slowly.
  • In the secondary response to T dependent antigens, there is a very high antibody production that comes about very quickly.
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8
Q

List the two most common locations where lymphocytes are found.

A

1 - In lymph nodes.

2 - In the spleen.

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9
Q

How long will an individual lymphocyte remain in a lymph node before migrating?

A

12-24 hours.

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10
Q

Via which structures do lymphocytes enter lymph nodes?

A

1 - High endothelial venules.

2 - Afferent lymph vessels.

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11
Q

Via which structures do lymphocytes exit lymph nodes?

A

Efferent lymphatic vessels.

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12
Q

List the two lymph ducts.

A

1 - Thoracic duct.

2 - Right lymphatic duct.

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13
Q

Where does lymph empty into from the lymph ducts?

A

The venous circulation.

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14
Q

What is the difference between primary and secondary lymphoid organs?

A
  • Primary lymphoid organs generate lymphocytes from immature progenitor cells.
  • Secondary lymphoid organs are the locations where lymphocytes are activated.
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15
Q

List the 2 primary lymphoid organs.

List 5 secondary lymphoid organs.

A

Primary lymphoid organs:

1 - Bone marrow.

2 - Thymus.

Secondary lymphoid organs:

1 - Lymph nodes.

2 - Tonsils.

3 - Spleen.

4 - Peyer’s patches.

5 - Mucosa associated lymphoid tissue (MALT).

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16
Q

List 8 locations where mucosa associated lymphoid tissue (MALT) is found.

A

1 - GI tract.

2 - Nasopharyngeal tract.

3 - Thyroid gland.

4 - Breast.

5 - Lungs.

6 - Salivary glands.

7 - Eyes.

8 - Skin.

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17
Q

Why is it advantageous for lymph to circulate around the body?

A

To increase the chances of encountering an antigen.

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18
Q

How many lymph nodes are there in the body?

A

700.

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19
Q

What enters lymph nodes via afferent lymph vessels?

A

Dendritic cells.

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20
Q

List the layers of a lymph node.

A

1 - Cortex.

2 - Paracortex (T zone).

3 - Medulla.

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21
Q

What is contained within the cortex of a lymph node?

A

Follicles.

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22
Q

What are germinal centres?

Where are they located?

A
  • The sites where mature B cells proliferate, differentiate, and mutate their antibody genes through somatic hypermutation.
  • They are located in B cell areas in the follicles of the cortex.
23
Q

In which area of a lymph node do high endothelial vessels empty?

A

The paracortex (T zone).

24
Q

What is meant by an extrafollicular antibody response?

Where does extrafollicular growth occur?

Where does follicular growth occur?

A
  • In adaptive antibody responses, B cells are induced to grow either in follicles or in extrafollicular areas as plasma cells.
  • Extrafollicular growth occurs in the medullary cords of lymph nodes and in the spleen.
  • Follicular growth occurs in the spleen and in germinal centres of lymph node follicles.
25
Q

List 2 cells that can be found within the medulla of a lymph node.

A

1 - Plasma cells.

2 - Macrophages.

26
Q

Describe the histological organisation of the spleen.

A
  • The spleen is formed of red pulp and white pulp:
  • The white pulp is organised into follicles.
  • T zones traverse the follicles.
  • Marginal zones line the follicles.
  • The remainder of the spleen is red pulp.
27
Q

List 3 cells that can be found within the red pulp of the spleen.

A

1 - Macrophages

2 - RBCs.

3 - Platelets

28
Q

List 3 cells that can be found within the white pulp of the spleen.

A

1 - Dendritic cells.

2 - T cells.

3 - B cells.

29
Q

List 4 characteristics of T-dependent antibody responses.

A

1 - T-dependent responses are required for switching to IgG, A and E.

2 - T-dependent responses are required for high-affinity antibody production.

3 - T-dependent responses are required for the longest-lived antibody responses.

4 - T-dependent responses are required for B cell memory.

30
Q

What type of antibody responses occur in extrafollicular foci?

A

Both T-dependent and T-independent responses.

31
Q

What type of antibody responses occur in germinal centres in the spleen?

A

T-dependent responses only.

32
Q

List the processes that occur at the beginning of antibody responses to protein antigens.

A

1 - An antigen-specific B cell binds to an antigen via the B cell receptor.

2 - The antigen is internalised by receptor-mediated endocytosis.

3 - A high density of specific antigen fragments is presented.

33
Q

List 4 molecules involved in the presentation of specific antigen fragments upon endocytosis of an antigen.

A

1 - MHC class 2.

2 - CD80.

3 - CD86.

4 - CD40.

34
Q

What is the difference between B cell and dendritic cell uptake of antigens?

A

Specificity - B cells are highly specific due to the specificity of the B cell receptor, whereas dendritic cells are not specific in what they take up.

35
Q

What is B cell activation necessary for?

How are B cells activated?

A
  • B cells must be activated in order to differentiate into plasma cells.
  • B cells are activated by receiving signals from CD4+ T cells.
36
Q

Define cognate interaction.

A

The interaction between dendritic cells, CD4+ T cells and activation-induced B cells during T-dependent responses.

37
Q

List 4 molecules that are involved in cognate interaction.

On which cells are these molecules found?

A

1 - CD40 (B cells).

2 - CD40L (T cells).

3 - ICOSL (B cells).

4 - ICOS (T cells).

38
Q

List 4 cytokines that reinforce the signals provided by cognate interaction.

A

1 - IL-4.

2 - IL-6.

3 - IL-21.

4 - IFN gamma.

39
Q

Describe the process of cognate interaction between a B and T cell.

Where does this interaction take place?

A
  • A physical cell-cell interaction must occur between B and CD4+ T cells, which requires B cell binding an antigen via the BCR, then processing and presenting the antigen to the T cell.
  • The interaction is either MHCII-TCR or CD40-CD40L.
  • This interaction occurs in the T zone of lymph nodes or the spleen.
40
Q

Where in secondary lymphoid organs are B cells activated by T cells in response to T-dependent antigens?

List 2 possible locations where antigen-activated B cells migrate after being activated by a T cell.

What happens to the B cells once they migrate to these areas?

A
  • B cells can be activated in the T zone. They then migrate to:

1 - To the medullary cords, where they differentiate into extrafollicular plasmablasts.

2 - To the follicles, where they form germinal centres.

41
Q

How does the initiation of T-independent antibody responses differ from that of T-dependent responses?

A

With T-independent responses, there is no cognate interaction between dendritic cells, T cells and B cells, so B cells travel through the T zone as antigen-activated B cells and migrate to the medullary cords where they differentiate.

42
Q

List 4 cells that can be found in a germinal centre.

A

1 - Centroblasts.

2 - Centrocytes.

3 - Follicular dendritic cells.

4 - Follicular T helper cells.

43
Q

Describe the organisation of a germinal centre.

A
  • A dark zone and a light zone form two halves of the inner circle.
  • The mantle zone surrounds the inner circle.
44
Q

What are centroblasts?

Where are they found?

A
  • Proliferating B cells that undergo somatic hypermutation for affinity maturation.
  • They are found in the dark zones of germinal centres.
45
Q

What are centrocytes?

Where are they found?

A
  • B cells that have undergone affinity maturation (as centroblasts) and are out of the cell cycle.
  • They are found in the light zones of germinal centres.
46
Q

What is the function of follicular dendritic cells?

Where are they found?

A
  • They are involved in the selection of memory B cells by presenting antigens to potential memory cells, of which only centrocytes with high affinity B cell receptors can bind (centrocytes compete for this antigen).
  • They are found in the light zone of the germinal centre.
47
Q

What are follicular T helper cells?

Where are they found?

A
  • T cells that give survival signals to centrocytes.

- They are found in the light zone.

48
Q

What is activation-induced cytidine deaminase (AID)?

What is its function?

A
  • A protein expressed in B cells.

- It is required for class switch recombination and Ig V gene hypermutation.

49
Q

What is B cell lymphoma-6?

A

The master transcription factor for commitment of germinal centre B cells, and is required for the generation of follicular CD4+ T cells.

50
Q

Which interleukin is important for the generation of follicular CD4+ T cells?

A

IL-21.

51
Q

What is blimp-1?

A

A transcription factor required for the plasma cell programme.

52
Q

After priming by a T cell, what is the functional difference between B cells that migrate to extrafollicular areas in the medullary cords and B cells that undergo a follicular response?

A
  • In extrafollicular responses, B cells differentiate to become IgM and IgG plasma cells, producing antibody of modest affinity (similar to T-independent responses).
  • In follicular responses, B cells form germinal centres that give rise to class-switched plasma cells, producing antibody of high affinity and to memory B cells.
53
Q

Where does Ig V gene hypermutation occur?

A

In centroblasts in the dark zone.

54
Q

Summarise the germinal centre reaction.

A

1 - A centrocyte that has emerged from the dark zone as a centroblast having undergone somatic hypermutation and exited the cell cycle competes for a specific antigen bound to follicular dendritic cells.

2 - In the light zone, a centrocyte that has bound an antigen on a dendritic cell seeks cognate interaction with a follicular T cell.

3 - The selected centrocytes are activated and differentiate into plasma cells or memory B cells, and those that are not selected die by apoptosis.

IIH (26 decks)

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