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PMI > PMI02-2005 Adaptive immunity: B cell response > Flashcards

PMI02-2005 Adaptive immunity: B cell response Flashcards

1
Q

Where do B lymphocytes originate?

A

Stem cells in the bone marrow

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2
Q

What are the functions of antibodies?

A

Attach to host tissues
Activate complement
Enhance phagocytosis
Induce degranulation of mast cells, eosinophils and neutrophils

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3
Q

What is the structure of an antibody?

A

It has 2 identical pairs of light chains and 2 identical pairs of heavy chains that are bound by disulphide bonds
Both heavy and light chains are divided into variable and constant regions

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4
Q

What does the variable region of the antibody contain?

A

The antigen-binding site

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5
Q

what is an antigen?

A

any molecule that binds specifically to an antibody

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6
Q

What is an epitope?

A

Specific site on the antigen that binds to the antibody

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7
Q

What is an immune complex?

A

Antibody bound to antigen

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8
Q

How many antibody classes are there?

A

5

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9
Q

What are the differences between the different antibody classes?

A

They differ in the number of immunoglobulin regions in the Fc region

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10
Q

What is class switching?

A

As the antibody response continues, B cells change the class of antibody so they produce antibody at a more suitable rate for elimination

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11
Q

What happens to the structure of antibodies during class switching?

A

The constant region of the heavy chain changes but not the variable region, therefore antigen specificity stays the same

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12
Q

What is the effector function of IgM?

A

IgM is a strong activator of complement binding with a high affinity for C1q because it has 5 times as many C1q binding sites

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13
Q

What is the effector function of IgG?

A

It is the only antibody to cross the placenta and provide protection for the infant
It has 4 sub classes: IgG1, IgG2, IgG3 and IgG4
IgG1 and IgG3 bind with higher affinities for Fcy receptors

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14
Q

What is the effector function of IgA?

A

IgA binds to Fca receptors on macrophages and neutrophils, which promotes phagocytosis and destruction
This results in degranulation and release of compounds that are highly toxic to pathogens

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15
Q

What is the effector function of IgE?

A

Largely bound to high affinity Fcy receptors on mast cells
Cross linking of IgE/ Fc receptor causes degranulation- release of histamine, serotonin, proteases, cytokines and leukotrienes

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16
Q

What are the 2 ways complement activation can kill pathogens?

A

Lysis by C9 formation

Phagocytosis of the pathogen mediated by C3b receptors

17
Q

What antibodies produce a Th1 response? what does this result in?

A

IgG1 and IgG3

Results in phagocytosis and destruction of pathogen

18
Q

What antibody mediates Th2 response?

A

IgE

19
Q

What does the Th2 response result in?

A

Degranulation- release of histamine, serotonin, proteases, cytokines and leukotrienes
This attracts lymphocytes, eosinophils, neutrophils and macrophages

20
Q

What is receptor editing?

A

Each B cell that expresses sIgM and sIgD that recognise self antigens undergo apoptosis or undergo further DNA rearrangement of light chain of the surface Ig

21
Q

What occurs to B cells that do not recognise self antigens or bind weakly?

A

Migrate to the spleen and lymph nodes

22
Q

How are B cells activated?

A

There is binding of sIgM and sIgD on the B cell to antigens that deliver signal 1
The B cell acts as an antigen presenting cell
Antigen is internalised by the B cell, then undergoes proteolytic antigen processing with peptide products presented in association with MHC II, which are exported to the surface of the B cell
Th cell recognises MHC complex and delivers further activating signals to the B cell via CD40
Th cell secretes cytokines that induce B cell proliferation, and production of antibodies

23
Q

What does rapid proliferation and differentiation of B cells give rise to?

A

Plasma cells that migrate to the bone barrow

24
Q

How long do plasma cells live?

A

2-3 days

25
Q

What do naive B cells produce when activated initially?

A

IgM and IgG

26
Q

What interleukins induce switching to IgE and IgG1?

A

IL-4

27
Q

What interleukins induce switching to IgA and IgG3?

A

IL-21

28
Q

What occurs if IL-4 is secreted as well as IL-21?

A

IgA switching does not occur

29
Q

What is somatic hypermutation of B cells and class switching initiated by?

A

Activation Induced Cytidine Deaminase (AICD)

30
Q

What is the function of AICD?

A

Converts cytosine to uracil and therefore breaks correct base pairing
Repairing this lesion introduces random DNA mutations

31
Q

What is somatic hypermutations?

A

Mechanism that introduces point mutations in V region axons during RNA transcription that exposed single stranded DNA
Mutated forms of antigen receptors that have higher affinity for antigens will be selected

PMI (16 decks)

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