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IMM005 > Antigen recognition: B cells and antibody > Flashcards

Antigen recognition: B cells and antibody Flashcards

1
Q

What model does immunological recognition operate through?

A

Lock and key model

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2
Q

On what scale do antibodies act on?

A

Less than 1 nm

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3
Q

Can antibodies recognise the same virus after is changes through evolutionary mechanisms?

A

No

Recognition is incredibly specific

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4
Q

Describe Ehrlich’s side chain theory

A

Observed that when injected a goat with toxin from a bacteria and then injected the same bacteria, no effect would be observed

Hypothesised the goat made something specific to the organism they injected

Important since the goat had never been exposed to the bacteria before

Ehrlich hypothesised this was because cells with specific shapes on their surface bound to the bacteria, which triggered them to make more of the specific receptor in soluble form

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5
Q

Describe Burnet’s clonal theory

A

Ehrlich was proven righ by Australian scientist in the 1950s

Instead of one cell with many different receptors, he thought there would be many cells with different receptors

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6
Q

What happens when an antibody closely binds to a specific antigen?

A

Produces soluble material

Specific cell divides so you have more cells upon secondary infection

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7
Q

How many cells have a specific antibody receptor?

A

100 cells display one specific receptor

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8
Q

What are the two main goals of adaptive immunity?

A

Recognising molecular change

Creating large diversity in receptors

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9
Q

What are antibodies?

A

Protein receptors

Part of a larger protein structure which acts as activators of intracellular mechanisms

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10
Q

What is the shape of an antibody?

A

Dimer within a dimer

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11
Q

What bonds bind together the heavy and light chains of the antibody?

A

Disulphide bonds

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12
Q

What is the role of the heavy chain?

A

Anchors the protein receptor to the cell membrane

Interacts with Fc surface receptors and some proteins of the complement system

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13
Q

Which cells contain Fc receptors?

A

Follicular dendritic cells

Natural killer cells

Macrophages

Neutrophils

Eosinophils

Basophils

Human platelets

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14
Q

Is the constant region the same for all B cells?

A

Yes

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15
Q

What is the function of the light chain?

A

Makes up part of the variable region which acts as an antigen recognition site

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16
Q

What is the complementarity determining region?

A

Flat surface

Determines how molecules bind to the antibody

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17
Q

Examples of antigen targets of B cells

A

Proteins

DNA

Sugar

Small molecules

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18
Q

Describe the bonds between proteins and B cell receptors

A

Bonds form through close apposition of surfaces which have to exactly match

The attraction results from molecules getting close together

Explained through the nature of proteins - commonly make Van der Waals forces

19
Q

How big is the area that proteins bind to on antibodies?

A

6 aa by 6 aa

20
Q

Describe the bonds between DNA and B cell receptors

A

Charged interactions

Lie on surface

21
Q

What type of structure does DNA represent?

A

A rigid structure

22
Q

Describe the bonds between small molecules and B cell receptors

A

Penetrate between loops to form tighter binding

23
Q

What allows for the antibody-antigen interaction to be in equilibrium?

A

Lack of covalent bonds

24
Q

Is the antibody-antigen interaction in equilibrium?

A

In theory they should be

In practice the equilibrium is favoured so far towards the complex formation, it is considered practically irreversible

25
Q

What governs the equilibrium?

A

The affinity constant

In the example of antibodies and antigens, the affinity constant is so high that is favours the formation of the complex

26
Q

What is the affinity constant between antibody and antigens?

A

10^7

10^8

27
Q

What happens to the antigen when it attached to the antibody?

A

It remains attached until it becomes degraded

28
Q

When does the generation of antibody diversity occur?

A

During B cell development in the bone marrow

29
Q

When does the generation of antibody diversity end?

A

When the B cells have left the bone marrow

30
Q

How is the diverse population of antibodies produced?

A

Billions of possible sequences produced by less than 200 genes

31
Q

How many variable minigenes are there?

A

40

32
Q

How many diversity minigenes are there?

A

27

33
Q

How many joining minigenes are there?

A

6

34
Q

Describe the genetics behind anditbody formation

A

Genes that encode antibodies are found in one locus

This locus is divided into minigenes coding one part of the final molecule

The minigenes are stitched together to make immunoglobulins

35
Q

What are the three minigenes coding for antibodies?

A

Variable

Joining

Diversity

36
Q

The DNA encoding antigens are the same to the germline

TRUE or FALSE

A

FALSE

A random process selects one V, J and C gene and stitches them together

The bits in between are thrown away

37
Q

Features of the VDJ recombination process

A

Irreversible - can’t use the regions you have thrown away

Allelically exclusive - you rearrange either the maternal or paternal allele and switch off the other allele

38
Q

Mechanisms of antibody diversity

A

V, D, J recombination

Imprecise joining of minigenes - recombinational inaccuracies

Independent light and heavy chain combination

Somatic hypermutation

39
Q

Describe how independent light and heavy chain combination contributes to antibody diversity

A

Two loci encode the light chain: kappa and lambda

The locus which encodes the light chain is randomly selected

These are chosen randomly and combined with the IgH (heavy chain)

40
Q

Which enzymes mediate VDJ recombination?

A

RAG-1

RAG-2

41
Q

How do RAG enzymes recognise V, D and J segments?

A

Recombinational signal sequences flanking V, D and J gene segments

42
Q

What are the two deliberate recombinational inaccuracies which increase antibody diversity?

A

Enzyme mediated deletion

Addition

43
Q

What is the source of antibody wastefulness?

A

VDJ recombinational inaccuracies

If the process of deletion or addition does not happen in 3s, a frameshift mutation causes the protein not to become transcribed

44
Q

What are mechanisms aimed at combating the wasteful process of recombinational inaccuracies?

A

Recombination mechanisms

Switching on the alternative allele

IMM005 (17 decks)

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