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Immunology > L5. Antigen Recognition by B and T Lymphocytes > Flashcards

L5. Antigen Recognition by B and T Lymphocytes Flashcards

1
Q

What are the 3 overall differences between the innate and immune responses?

A

Adaptive immune responses are initially slower to develop than innate responses, but show SPECIFICITY and MEMORY.

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2
Q

What do B and T lymphocytes recognise Antigens through?

A

specific ANTIGEN RECEPTORS

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3
Q

Where do a) B b) T Lymphocytes gain their antigen receptors?

A

a) Bone marrow

b) Thymus

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4
Q

How many types of antigen receptor do a B or T lymphocyte have, why is this important and what happens if stimulated?

A

Single B or T cells express single antigen receptors. Cells with appropriate receptors undergo CLONAL SELECTION in response to antigen. Important as produces the right response as the right time.

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5
Q

What two forms do antibodies (immunoglobulins) exist as and what is their function?

A
  1. Integral membrane proteins on B lymphocytes
    >Antigen receptors
  2. Soluble proteins secreted by plasma cells (when B-cell is stimulated)
    >Antigen eliminators
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6
Q

Is most of our knowledge of antibodies based off of soluble or integral membrane type?

A

Most of what we know about antibody structure is based on studies of soluble antibodies (Paul Ehrlich).

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7
Q

How many light and heavy chains does an antibody have?

A

Made up of 4 polypeptide chains (2 light chains and
2 heavy chains)

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8
Q

How was it found out that an antibody is made up of 2 types of chains of differing weights?

A

Reduced the molecule, and alkylated it to stop it making bonds.
Ran them on gel to see the 2 light and 2 heavy chains.

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9
Q

What are the 2 fragments of antibody called and what holds them together?

A

> FAB: Fragment antigen binding

> Fc: Fragment crystallisable (crystalized in solution)

> Hinge region (usually disulphide bonds)

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10
Q

Which fragment of antibody binds with antigen?

A

FAB

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11
Q

What is the role of the Fc region of the antibody and 2 examples of its function?

A

> Interacts with elements of the innate immune system (antigen elimination)

> Binds to receptors on phagocytes,NK cells, neutrophils, eosinophils (opsonisation), can also interact with complement first components to activate cascade.

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12
Q

What is F(ab’)2 and how is it made?

A

When cleaved with papain, it cleaved the antibody so that both Fab arms are connected and were divalent so could bind to 2 antigen at once (mimics a physiological antibody showing an intact Fab region could bind to 2 antigen).

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13
Q

How are immunoglobulins (antibodies) classified?

A

There are five classes of immunoglobulin that differ in the amino acid sequence of their heavy chains (refer to heavy chain by corresponding Greek letter)

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14
Q

What are the 5 heavy chain classes of immunoglobulin (antibody), where are they commonly found and what is their function?

A
  1. IgG (γ)
    >Main class in serum and tissues important in secondary responses (encountering pathogen for second time)
  2. IgM (μ)
    >Important in primary responses (always made first when come across a pathogen and when immune system is developing).
  3. IgA (α)
    >In serum & secretions protects mucosal surfaces (in tears, mucus, milk; most infections occur in mucosal surfaces)
  4. IgD (δ)
    >?
  5. IgE (ε)
    >Present at very low levels involved in protection against parasites and allergy
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15
Q

What are the 2 classes of light chain immunoglobulins (antibodies)?

A

kappa (k) and lambda (λ).

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16
Q

What is a difference between light chain classification of antibodies and the heavy chain classification?

A

These are not class restricted i.e. can have IgGk or IgGλ antibodies.

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17
Q

What are Myeloma proteins and what is their use?

A

> Myeloma proteins (myeloma = cancer of plasma cells)

> Myeloma is cancer of antibody producing plasma cells, these divide out of control producing an antibody of a single type; giving scientists a way to purify and isolate antibodies of a specific type.

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18
Q

What are the 3 important discoveries about antibodies that protein sequencing from myeloma proteins produced?

A
  1. Antibodies contain constant and variable regions
  2. Antibodies are comprised of homologous domains
  3. The variable region domains contain 3 hypervariable regions
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19
Q

What are the a) Variable b) Constant regions of an antibody, what chains do they make up, are they class specific and what is their function?

A

a) VARIABLE (V) regions
>Bind antigen.
>Differ between antibodies with different specificities.
>N terminus of heavy and light chains.

b) CONSTANT (C) regions
>Same for antibodies of a given H chain class or L chain type.
>Allows antibody to interact with innate immune system.
>Makes up most of light and heavy chains.

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20
Q

What is meant by antibodies being comprised of homologous domains?

A

Regions of sequence homology identified (~110 amino acids always including 2 cysteines for intramolecular disulfide bonds- between immunoglobulin domains) and intermolecular disulphide bridge formation (between Fc and Fab arms).

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21
Q

What holds together a) each globular domain of an antibody b) Seperate chains?

A

a) Each globular domain stabilised by an intra-chain disulphide bond (between cysteine residues withinn the same polypepttide chain, so each heavy chain is joined by these but then is joined to the adjacent light ot heavy chain by intermolecular disulfide bonds).

b) intermolecular disulphide bridge formation (between light and heavy chains), between cysteine residues on seperate polypeptide chains.

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22
Q

Why is the hinge region more flexible and more prone to proteolysis?

A

Hinge is not tightly folded, lots of proline residues (more susceptible to proteolysis)-so is made of cyesteine (for disulfide bonds) and proline residues mainly (for flexibility of fab arms for indepentent binding ot antigen).

23
Q

How was the structure of the homologous globulin domains confirmed?

A

Domain structure confirmed by X-ray crystallography of Fab and Fc fragments

24
Q

Describe the typical arrangement of an immunoglobulin fold for a) Constant domains b) Variable domains

A

a) 7 beta sheets held together by less structured loop regions.

b) 9 beta sheets held together by less structured loop regions.

25
Q

Why is the immunoglobulin fold found in all members of the immunoglobulin gene superfamily?

A

As it descended from one primordial gene.

26
Q

What are all parts of the Immunoglobulin Gene Superfamily involved in?

A

All parts of family involved in immunity: generally involved in recognition, binding, adhesion (Found in nervous system too showing links between this and immune system).

27
Q

What is the largest gene family in humans?

A

The Immunoglobulin Gene Superfamily (usually receptors but also has soluble antibodies)

28
Q

Why is the immunoglobulin domain structure easily persevered through evolution?

A

The immunoglobulin domain structure folding pattern can be persevered as the beta pleated sheets can be kept with little variation while evolving the loops, so the overall folding patterns is conserved.

29
Q

What is the role of the 3 hypervariable regions of an antibody?

A

To bind with antigens.

30
Q

How many amino acids usually make up a hypervariable region?

A

7-12 amino acid residues

31
Q

What provides structure to the hypervariable regions?

A

The hyper variable loops are held together by less variable framework regions which provide structure (surrounding constant beta-sheets in the immunoglobulin fold)

32
Q

What is another name of hypervariable regions?

A

Hypervariable regions = also known as Complementarity Determining Regions (CDRs

33
Q

What type of interaction occur between antibody and antigen, name 4 examples?

A

Non-covalent (Electrostatic interactions, Hydrogen bonds, Van der Waals forces, Hydrophobic interactions)-all are reversable

34
Q

What makes it so an Antibody:Antigen interaction will always be specific with high affinity?

A

Non-covalent interactions are Individually weak, but if many form simultaneously; Means if an antibody has many binding points of high affinity, the many weak bonds will summate to make a strong affinity.

35
Q

What is the name of the specific part of an antigen that an antibody binds to?

A

Epitope (A few amino acids residues on the antigen molecule that the antibody recognises).

36
Q

How does an antibody form many weak non-covalent interactions with an antigen, and what is useful about this?

A

Hypervariable regions in forms a large interface with the antigen allowing lots of weak interactions to occur simultaneously, So antibodies can bind specifically and with high affinity (tighter than enzymes)

37
Q

What is different in the structure of B cell receptors and soluble antibodies?

A

Have extra 26 hydrophobic amino acids allowing to sit in membrane, found at C-terminus (inserted on lipid bilayer).

38
Q

What types of antibodies are often expressed on B cells when developing?

A

Most B-cells express IgM and/or IgD as B-cell receptors when developing.

39
Q

What is the role of B cell receptors, and what can’t they do?

A

Recognise and bind to antigen, but cannot generate a signal.

40
Q

What is needed for a signal to be generated when B cell receptors bind with antigen?

A

Membrane immunoglobulins are associated with two other proteins, Igα and Igβ that facilitate signalling (Monomer of IgM, has to be associated with Ig-alpha and beta which have longer cytoplasmic domains which can signal).

41
Q

How do Igα and Igβ allow for B cell receptor signalling?

A

Igα and Igβ contain a single ITAM (Immunoreceptor Tyrosine Activation Motif) in their long cytoplasmic domains.
ITAMs can be phosphorylated, triggering downstream signalling.

42
Q

What does ITAM stand for?

A

Immunoreceptor Tyrosine Activation Motif

43
Q

What does Immune Repertoire mean?

A

The antibodies we can make in our lifetime

44
Q

What is the immune repertoire for a) Antibody receptors b) T cell receptors, can this be produced in our life time?

A

a) ~10^14 antibody receptors

b) ~10^18 T cell receptors

> We don’t make this many as we don’t live that long, in theory we could.

(the raw genetic recombination potential for diversity might initially appear higher for TCRs, the additional mechanisms of somatic hypermutation and class switching unique to B cells can produce an antibody repertoire of immense diversity, potentially rivaling or exceeding that of TCRs in practice.)

45
Q

What is the main determinant of antibody diversity?

A

Variations in the sequence and length of CDRs (hypervariable regions) are the main determinants of antibody diversity.

46
Q

What section of CDRs (Hypervariable region) tends to be most variable in length and sequence?

A

CDR3 tends to be most variable in length and sequence

47
Q

Which chain contributes more to antigen binding and why?

A

> Heavy chain generally contributes more to antigen binding and is more variable than the light chain

> Heavy chains tend to be more variable than light chains in hypervariable regions.

48
Q

How does Diversity arise in antibody genes?

A

Diversity arises by somatic recombination and mutation of a limited (small) number of inherited antibody gene segments, which make up the V regions.

49
Q

What did Susumu Tonnegawa show caused diversity in differentiating B cells?

A

A light chain had a single constant region gene, but multiple variable genes, then after B cells differentiate this is rearranged so a particular variable region genes lies next to a constant region gene to code for a particular light chain.

50
Q

What is the only cells which undergoes rearrangement of genes (somatic recombination)?

A

B and T cells

51
Q

What do the 3 sets of immunoglobulin genes code for and what chromosome are they found on?

A

> Set coding for heavy chains, kappa chains, and Lambda chains

  1. Heavy (H) chains: genes found on chromosome 14
  2. Kappa (k) chains: genes found on chromosome 2
  3. Lambda (λ) chains: genes found on chromosome 22
52
Q

Explain what a Kappa gene is made up of in the germline DNA and in the finished protein

A
  1. In the germline DNA Kappa chains have a single constant region with multiple downstream variable regions.
  2. In the finished proteins the constant exon (CK) is joined to a variable region which is made up of VK and JK (Variable Kappa exon and Joining Kappa exon).
53
Q

For a Kappa gene what is the JK exon for?

A

Joining Kappa exon joins the VK (variable Kappa exon) to the CK (Constant variable exon).

Immunology (20 decks)

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