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Flashcards in MCB Lecture 46 B cells Deck (42)
0

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

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

1

What are the components of the adaptive immune system?
Which lymphocytes are responsible for each?

Cellular: T lymphocytes
Humoral: B lymphocytes

2

What are the receptors found on B lymphocytes called?

B Cell Receptors BCR
Antibodies
Immunoglobulins
Antigen receptors

3

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

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

4

What is the function of BCR?

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

5

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

Lipids
CHOs
Nucleic acid
Protein

6

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

Epitope
Antigenic determinant
Determinant

Can be linear of discontinuous

7

What is the function of B lymphocytes?

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
4. Classical pathway of the complement system; opsonisation

8

Describe the locations involved in the production of B cells

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

9

Where do B cells spend most of their time?

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

10

What are the divisions of lymphoid tissues?
List some of the organs in each

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

11

Describe what is meant by Tolerance

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

12

How are autoimmune diseases caused?

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

13

How do lymphocytes come in contact with antigens?

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

It is here that the lymphocytes come in contact with antigens

14

Describe how B cells become activated
What is the analogy?

Where does this occur?

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

15

What are the features of clonal expansion? (2)

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

16

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

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

Differentiate between the antigens that activate B and T lymphocytes

B cells: free floating antigens interact with the BCR
T cells: antigens bound to MHC interact with TCR

18

Where does clonal selection occur?

In the secondary lymphoid tissue

19

What is the function of memory cells?

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

20

What is the function of plasma cells?

These synthesise and secrete antibodies

21

Describe the function of antibodies

Antibodies coat the pathogen by binding to the antigen
Removal of the pathogen

22

Describe briefly the structure of antibodies

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

What is the Fc region?
What different forms can it take?

This is the constant region of the antibody
There are 5 different isotopes

24

What is the Fab region?
What different forms can it take?

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

What is the structure, function and location of IgA?

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

What is the structure, function and location of IgM?

Pentamer, j chains and disulfide bonds

Present on the surface of naive B cells

Function
Neutralises toxins
Triggers the classical pathway

27

What is the structure, function and location of IgE?

Monomer

Bound to Mast cells

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

28

What is the structure, function and location of IgG?

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

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

IgG

IgM

30

Which isotype binds to the FcR on phagocytes?

IgG

31

Which isotype triggers release of granules?

IgE

32

Which isotype is normally found as a pentamer?

IgM

33

Which isotype is normally found as a dimer?

IgA

34

Describe the different possible affinities between epitope and Fab

High affinity
Low affinity

35

Which isotype is found on naïve B cells?

IgM

36

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

IgM

37

Describe how B cells can undergo isotype switching

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

What are the features f isotype switching? (3)

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

39

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

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

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

NK Cells have FcR
Binding of antibodies (constant region) triggers degranulation

41

Which isotype is normally transferred in passive immunity?

IgG

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