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Theme 4 > B cells and antibody > Flashcards

B cells and antibody Flashcards

1
Q

What is an antibody

A

Antibodies are Y- shaped antigen-specific proteins produced by B lymphocytes

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2
Q

What is an antigen

A

a specific protein on the surface of a pathogen. It is made up of an epitope. Each epitope is specific to specific pathogens

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3
Q

Define ‘antibody isotype’

A

Different heavy chain that forms different constant region (Fc) but have the same variable(Fab) region

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4
Q

Describe and draw the structure of an antibody

A

An antibody is made up of 2 identical heavy chain and 2 identical light chain. Both each are made up of a variable region(FAB) and a constant region(Fc)

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5
Q

Define somatic recombination

A

The combination of genes from multiple segments of DNA that codes for the variable region of an antibody.
no. of genes in 1 * no. of genes in 2 * no. of genes in 3

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6
Q

Define affinity maturation

A

Affinity maturation involves the process of class switch and somatic hypermutation as B- cells divide and increase in number after clonal selection

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7
Q

The variable region (the part that binds onto the epitope of the antigen) is made up of:
A. Light chains only
B. Heavy chains only
C. Light and heavy chains

A

C. Light and heavy chains

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8
Q

Antibodies can be present on B cells surface as receptors– as well as secreted into the bloodstream where they circulate as free proteins.
True or false?

A

True

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9
Q

What is physio-chemical affinity

A 
Key-lock model
Specific antibody(specific variable region-Fab) binds onto specific epitope on antigen
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10
Q

What is an immunoglobulin (Ig)

A

Antibody

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11
Q

List 5 types of antibody isotypes

A
  1. IgM
  2. IgA
  3. IgD
  4. IgE
  5. IgG

Remember: MADE G

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12
Q

List 4 properties of IgM antibody isotype

A
  1. Responsible for early stage immunity (primary response)
  2. Doesn’t bind antigen well so makes up for it by forming a pentamers (Increase S.A)
  3. Pentamers are held by joining (J) chain.
  4. As immune response progress, IgM switches to a different antibody isotype
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13
Q

List the 6 properties of IgA antibody isotype

A
  1. The only antibody that can cross mucosal surfaces
  2. Found in secretions e.g mucus in gut, saliva and tears
  3. Forms a dimer.
  4. Dimers are held together by J chains
  5. Protected from digestion by secretory component (S chain)
  6. Colostrum (forerunner of breast milk) is rich in IgA antibody isotype
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14
Q

List 3 properties of IgD antibody isotype

A
  1. IgD exists as a monomer
  2. Like IgM, it is produced during early immunity by B-cells
  3. Present on B cells surface
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15
Q

List 3 properties of IgE antibody isotype

A
  1. Exists as a monomer
  2. Responsible for allergic reactions
  3. Responsible for parasitic infection
  4. Coats Mast cells during mast cell activation
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16
Q

List 4 properties of IgG antibody isotype

A
  1. Exists as a monomer
  2. Main antibody for secondary response
  3. Neutralises toxins
  4. Opsonisation
17
Q

List 3 functions of antibodies

A
  1. When antibody is bound to B-cell surface. It acts as B-cell receptor
  2. By directly binding to epitopes/receptors that contains virus/toxins (toxin neutralisation)
  3. By binding to antigens then interacting with another element of the immune system e.g opsonisation after phagocytosis, mast cell activation and antigen presentation to CD4 T cells
18
Q

List 4 ways antibody binding to antigen can act on another element of the immune system

A
  1. Opsonisation after phagocytosis
  2. Mast cell activation for secretion of histamines
  3. Antigen presentation to CD4 T cells
  4. Antibody-dependent cellular cytotoxicity- NK Cells
19
Q

What is tetani and how does it occur

A

uncontrolled muscle contraction.

Clostridium Tetani bacteria releases tetanus toxins that causes muscle contraction

20
Q

How does antibody work on tetani

A

Antitoxin antibody binds onto tetanus released by clostridium tetani bacteria.
Antitoxins neutralises the tetanus toxin.

21
Q

List 3 things antibody can bind to

A
  1. Epitopes on antigens
  2. Receptors that contains virus
  3. Toxins
22
Q

Define Opsonisation

A

The process of coating a bacteria with antibody to reduce repulsion between the Phagocyte and the antigen (both are negatively charged). It enhances Phagocytosis

23
Q

Explain in 5 steps Mast cell activation

A
  1. Mast cells have surface Fc receptors
  2. Mast cells becomes coated by IgE antibody from circulation
  3. Appropriate antigen binds onto Fab region on IgE
  4. This causes the mast cell to degranulate, releasing histamine
  5. Mast cells are inappropriately activated during allergy
24
Q

What is antibody dependent cellular cytotoxicity (NK cell activation)

A

NK cells posses Fc region receptor. NK cell recognises antibody coated bacteria. NK cell kills the bacteria by non-phagocytic means

25
Q

There are a million pathogen. We need about a million different B-cells and therefore a million different antibodies. We only have about 25,000 genome.
How does this limited number of genes cater for the diversity of antibodies we need ?

A

SOMATIC RECOMBINATION.
For example - 3 DNA regions each containing different gene segments that makes up the variable region.
Total number of possible genes = number of segments in 1 * no. in 2 * no. in 3

26
Q

List 4 advantages of somatic recombination

A
  1. Huge diversity- antibodies can recognise any bacteria
  2. Large number of antibody can be made from a small area of DNA
  3. Resilience in different environment/against emergent pathogen
  4. Inherit gene segments, so get some benefit from evolutionary experience
27
Q

List 3 disadvantages of somatic recombination

A
  1. Many combinations will not work as it is generated randomly (some cant fit together biochemically and some will bind to self antigen)
  2. B cells with dysfunctional antibodies are mostly destroyed(deleted). This process is energy intensive
  3. Potential for autoimmune disease - incomplete deletion of B-cells that can damages self antigens
28
Q

Explain Clonal selection (3 marks)

A
  1. We are born with a unique set of B-cells. Few B-cells of each type
  2. During an infection, B cells with the best response to the antigen are SELECTED out
  3. These B cells DIVIDE and make clones of themselves. This is known as Clonal selection.
29
Q

When B cells divide in the antigen driven process, they do 2 things. what are they?

A
  1. Class switch - from IgM to IgG(higher affinity). Variable region remains the same.
  2. Somatic hypermutation- random mutations in the variable region of the antibody. daughter cells produce slightly different antibody. Further rounds of clonal selection pick out the best receptors.
    BOTH PROCESS IS KNOWN AS AFFINITY MATURATION
30
Q

List 2 process of Affinity Maturation (division of B cells during primary response)

A
  1. Class Switch

2. Somatic Hypermutation

31
Q

Mature B cells that become long lived are called

A

Memory cells

32
Q

Class switch occurs in primary and secondary response. True or false ?

A 
True
However class switch from IgM to IgG (higher affinity) is quicker and higher in secondary response.

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