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Miscellaneous > MCB Lecture 46 B cells > Flashcards

MCB Lecture 46 B cells Flashcards

0
Q

What are the components of the adaptive immune system?

Which lymphocytes are responsible for each?

A

Cellular: T lymphocytes
Humoral: B lymphocytes

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1
Q

What are the general characteristics of the adaptive immune response? (3)

A
  1. Slow
  2. Specific
  3. Magnitude increases with exposures
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2
Q

What are the receptors found on B lymphocytes called?

A

B Cell Receptors BCR
Antibodies
Immunoglobulins
Antigen receptors

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3
Q

Describe the copy number and variability of the receptors on a single B cell

A

There is only one type of receptor on each B cell, however there are many thousands of each receptor on each B cell

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4
Q

What is the function of BCR?

A
  1. They recognise and bind to antigens on pathogens that enter the body.
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5
Q

What are the broad groups of antigens that bind to BCRs?

A

Lipids
CHOs
Nucleic acid
Protein

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6
Q

What is the name of the region on an antigen to which the BCR binds?
Give some general facts about these areas

A

Epitope
Antigenic determinant
Determinant

Can be linear of discontinuous

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7
Q

What is the function of B lymphocytes?

A
  1. Become active when the BCR binds to an antigen (clonal selection)
  2. Divide and proliferate
    3a. Plasma cells make and secrete antibodies to further fight the infection
    3b. Memory cells wait for the next time that pathogen enters the body –> more rapid response
  3. Classical pathway of the complement system; opsonisation
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8
Q

Describe the locations involved in the production of B cells

A
  1. Develop from hematopoetic stem cells in the bone marrow of the major bones in the body
  2. Migrate to the blood
  3. Move into the lymphatics, where they wait until they come across their antigen
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9
Q

Where do B cells spend most of their time?

A

50% mucosal associates lymph tissue
40-50% lymph nodes
2% blood

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10
Q

What are the divisions of lymphoid tissues?

List some of the organs in each

A 
Primary lymphoid organs: where they develop
Bone marrow, thymus
Secondary lymphoid organs: where the lymphocytes reside when they become activated 
Lymph nodes
Tonsils
Adenoids
Mucosal associated lymphoid tissue
Peter cells of S.I.
Large intestine
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11
Q

Describe what is meant by Tolerance

A

This is the removal of auto reactive antigens; those that respond to self antigens

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12
Q

How are autoimmune diseases caused?

A

This is when auto reactive antibodies are not removed, and an immune response is launched against part of oneself

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13
Q

How do lymphocytes come in contact with antigens?

A

The ECF in tissues drain via afferent lymphatic ducts into the lymph nodes

It is here that the lymphocytes come in contact with antigens

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14
Q

Describe how B cells become activated
What is the analogy?

Where does this occur?

A

Clonal selection

A B cell expressing a unique BCR comes in contact with an antigen that matches the receptor.
The epitope binds lick a key in the BCR lock

This occurs in the secondary lymphoid tissues

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15
Q

What are the features of clonal expansion? (2)

A

Takes time
Lymphocyte divides and proliferates
Lots of ER now present in the selected cells for protein synthesis

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16
Q

What two types of cells are produced in clonal expansion of B cells?

A

Memory cells: remain in the lymph for the next time the same pathogen invades
Plasma cells: these synthesise and secrete antibodies (the same one as the B cell first expressed)

17
Q

Differentiate between the antigens that activate B and T lymphocytes

A

B cells: free floating antigens interact with the BCR

T cells: antigens bound to MHC interact with TCR

18
Q

Where does clonal selection occur?

A

In the secondary lymphoid tissue

19
Q

What is the function of memory cells?

A

These remain in the lymphatics for the next time that antigen gets inside the body

20
Q

What is the function of plasma cells?

A

These synthesise and secrete antibodies

21
Q

Describe the function of antibodies

A

Antibodies coat the pathogen by binding to the antigen

Removal of the pathogen

22
Q

Describe briefly the structure of antibodies

A

Two chains: heavy and light
There are two of each type of chain per antibody

There are two regions:
Fc: constant region
Fab: Variable region

23
Q

What is the Fc region?

What different forms can it take?

A

This is the constant region of the antibody

There are 5 different isotopes

24
Q

What is the Fab region?

What different forms can it take?

A

This is the variable region of the BCR
This is the region that binds to the epitope of the antigen

It can take an almost infinite number of forms

25
Q

What is the structure, function and location of IgA?

A

Dimer, J chain

Secreted over the mucosa into the gut for example

Function:
Prevents pathogens from binding to the mucosa
Binds to bacteria, toxins and viruses (via epitope)

26
Q

What is the structure, function and location of IgM?

A

Pentamer, j chains and disulfide bonds

Present on the surface of naive B cells

Function
Neutralises toxins
Triggers the classical pathway

27
Q

What is the structure, function and location of IgE?

A

Monomer

Bound to Mast cells

Function
Triggers degranulation: release of toxic substances from granules that kill the pathogen

28
Q

What is the structure, function and location of IgG?

A

Monomer

Found in plasma and tissue fluids

Binds to pathogens
The Fc part then binds to the Fc-receptor on phagocytes
Triggers phagocytosis of the bacterium

Trigger classical pathway of the complement cascade

29
Q

Which isotopes are involved with activating the classical pathway of the complement cascade?

A

IgG

IgM

30
Q

Which isotype binds to the FcR on phagocytes?

A

IgG

31
Q

Which isotype triggers release of granules?

A

IgE

32
Q

Which isotype is normally found as a pentamer?

A

IgM

33
Q

Which isotype is normally found as a dimer?

A

IgA

34
Q

Describe the different possible affinities between epitope and Fab

A

High affinity

Low affinity

35
Q

Which isotype is found on naïve B cells?

A

IgM

36
Q

Which isotype of Fc is secreted by B cells after they are first activated?

A

IgM

37
Q

Describe how B cells can undergo isotype switching

A

This is an irreversible process

The genes of the constant region are rearranged when being transcribed in gene transcription in B cells
The Fc region is now different

IgM -> IgG

38
Q

What are the features f isotype switching? (3)

A
  1. Irreversible
  2. Requires T cell and other external signals to determine which isotype we are switching to
  3. Accompanied by increased affinity
39
Q

What are the two ways that an individual can obtain specific immunity?

A

Passive: individual given antibodies to a specific antigen directly
Eg. When someone is infected with tetanus, they are transfused with the blood of someone who has made antibodies to tetanus, so that the response can be very rapid
Active: antigen presented to BCR in the body

40
Q

How do natural killer cells interact with the adaptive immune system?

A

NK Cells have FcR

Binding of antibodies (constant region) triggers degranulation

41
Q

Which isotype is normally transferred in passive immunity?

A

IgG

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