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Immunology > Antibody Structure and Function > Flashcards

Antibody Structure and Function Flashcards

1
Q

Basic composition of antibodies

A

Glycoproteins

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2
Q

Where are antibodies found?

A

Surface of B cells

Produces by plasma cells and released into blood serum and secreted fluids like saliva and milk

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3
Q

What do antibodies activate?

A

The classical complement pathway

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4
Q

3 major functions of antibodies + 3 other roles

A
  1. Opsonins to enhance phagocytosis
  2. Neutralize toxins and viruses by binding to the antigen
  3. Activating complement
  4. act as antigen receptors for B cells
  5. Mast cell degranulation (mainly IgE)
  6. Antibody dependent cell mediated cytotoxicity (ADCC)
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5
Q

5 classes of antibody?

A

IgG, IgM, IgA, IgE, IgD

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6
Q

Heavy chain of IgG

A

γ

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7
Q

Heavy chain of IgM

A

μ

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8
Q

Heavy chain of IgA

A

α

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9
Q

Heavy chain of IgE

A

ε

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10
Q

Heavy chain of IgD

A

δ

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11
Q

What are the 2 classes of light chains?

A

κ and λ

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12
Q

What holds the light chains together?

A

disulphide bonds and non-covalent interactions

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13
Q

What are globular domains?

A

Sections of about 110 amino acids held together by intrachain disulphide bonds

each light chain has 2 domains while the heavy chain has 4 domains + the hinge region

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14
Q

What is the V region

A

The variable region present on both the light and the heavy chains

  • variable AA sequence
  • where antibody interacts with antigen

Both heavy and light chains have 1 V region

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15
Q

What is the C region?

A

Constant region present in both the heavy and the light chains

  • constant AA sequence
  • the constant region of the heavy chains is where the effector activity occurs

Light chains have 1 C region. Heavy chains have 3 or 4

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16
Q

Which 2 classes of antibody have a J chain?

A

IgM and IgA

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17
Q

Which 2 classes of antibody have subclasses of the heavy chain

A

IgG and IgA

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18
Q

What are the IgA heavy chain subclasses?

A

α1 and α2

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19
Q

What are the IgG heavy chain subclasses?

A

γ1, 2, 3, and 4

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20
Q

Which is the more common form of light chain?

A

the kappa light chain is the default

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21
Q

What can affect antibody stability and interactions with other proteins ?

A

Glycosylation

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22
Q

Which three regions within the V region form the antigen binding site?

A

The hypervariable regions

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23
Q

Sequences rich in what amino acid constiture the hinge region?

A

Proline

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24
Q

What 3 classes of antibody have a true hinge region?

A

IdD, IgA, IgG

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25
Q

What domain of IgM and IgE has hinge region like properties

A 
Ch2 domain (additional heavy chain domain) 
-even though it lacks proline rich sequences
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26
Q

Differences in which region os the antibody determines half like, distribution, complement fixing, and Fc receptor binding?

A

Heavy chain constant region

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27
Q

What is the Fc region?

A

The fragment crystalizable region

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28
Q

What does proteolysis of IgG with papain yield?

A

2 identical Fab regions and 1 Fc fragment

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29
Q

What does proteolysis of IgG with pepsin yield?

A

Divalent F(ab’)2 fragment and a pFc’ fragment

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30
Q

What does reduction of IgG with mercaptoethanol yield?

A

2 heavy chains and 2 light chains

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31
Q

Antibodies produce what kind of response when injected into other species?

A

an antibody response

32
Q

What is an isotypic determinant and where is it located?

A

Located in the constant region

Define heavy chain classes/subclasses and light chain classes/subclasses within a species

33
Q

What is an allotypic determinant and where is it located?

A

Located in the constant region

Can vary from individual to individual (ie. non species specific)

34
Q

What is an idiotypic determinant and where is it located?

A

Located in HC and LC variable regions
-both the hypervariable and framework regions

Defined by the unique amino acid sequences that determine antibody specificity

35
Q

What occurs during opsonzation?

A

interactions between the Fc region and the Fc receptors on phagocytes promotes phagocytosis

36
Q

What occurs during antibody dependent cell mediated cytotoxicity?

A

the antibody acts as a receptor to enable recognition and killing of target cells by Fc receptor bearing NK cells

37
Q

What occurs during transcytosis?

A

Passage of antibody across epithelial layers to mucosal surfaces
-only certain classes, primarily IgA (IgM can as well)

38
Q

What effector function is unique to IgE?

A

Mast cell degranulation

39
Q

Which class of antibody can cross the placenta?

A

IgG

40
Q

Each light chain weighs about…

A

25 kDa

41
Q

Each heavy chain weighs about..

A

50 kDa

42
Q

What is the structure of IgG?

A

2 identical 50 kDa γ and 2 identical 25 kDa κ or λ chains

43
Q

How many subclasses of IgG heavy chains are there?

A

4 in humans

-each has a unique biological property

44
Q

What are the 5 main roles that IgG has?

A
  1. Neutralize
  2. Opsonize
  3. activate classical complement pathway
  4. mediate ADCC reactions
  5. Crosses placenta during pregnancy
45
Q

What is the structure of IgM and how does it differ between the expressed form and the secreted form?

A

Expressed as a monomer (2 μ chains, 2 κ or λ chains) on B cells

secreted by plasma cells as a pentamer containing a J chain

46
Q

What is the most abundant antibody in the blood serum and interstitial fluid?

A

IgG

47
Q

How many (of the 10 Fab regions) on IgM are able to interact with large antigens at a time?

A

5

48
Q

IgM is the first immunoglobulin class made by…? (2 cases)

A

Newborns and during a primary immune response

49
Q

The presence of the J chain in IgM allows it to…?

A

be transported across epithelial mucosa

-not as effectively as IgA

50
Q

What are the 2 main function of IgM?

A
  1. Agglutination of particulate antigens

2. Activator of the classical complement pathway

51
Q

Structure of IgA (2 forms)

A

as a monomer (2 α chains, 2 κ or λ chains) in serum

as a dimer (contains a J chain and secretory component) in mucosal secretions

52
Q

Where is dimeric IgA formed?

A

In plasma cells

-by addition of a J chain

53
Q

Where is the secretory component added to the dimer?

A

Added by the epithelial cels during the passage of IgA through glandular epithelial cells

54
Q

What is the purpose of the secretory component?

A

Protect the dimer from proteolysis by enzymes found in mucosal secretions

55
Q

What is the function of IgA in mucosal surfaces?

A

defends mucosal surfaces from microbial attack by inhibiting pathogen adherence

56
Q

What occurs to the IgA-antigen complexes ?

A

trapped in the mucus and eliminated by mechanical action

57
Q

What is the role of IgA in breastmilk?

A

Confers mucosal immunity on newborns

who only have IgM at this point, which has a hard time exiting the blood and getting into the tissues

58
Q

Formation of secretory IgA

A
  1. Plasma cell secretes dimeric IgA into the submucosa
  2. Poly-Ig receptor on inner side of epithelial cells binds the dimeric IgA
  3. Dimeric IgA taken up into a vesicle
  4. Addition of secretory component and enzymatic cleavage
  5. Secretory IgA released from the apical side of the epithelial cells into the lumen
59
Q

Why do you not find much IgM in mucosal secretions?

A

The secretory component is not large enough to protect the pentameric molecule from the proteolytic enzymes

60
Q

Structure of IgE

A

monomer consisting of 2 (heavy) ε chains and 2 (light) κ or λ chains

61
Q

What is the general distribution of IgE in serum?

A

Low generally

High in cases of allergy or parasitic infections

62
Q

What is the main function/mode of action of IgE

A

Bind to high affinity Fcε receptors on mast cells and basophils

63
Q

What causes mast cell and basophil degranulation?

A

Crosslinking of membrane bound IgE

  • 2 IgE molecules bound to the mast cell
  • Allergen comes and binds to the Fab regions of both IgE molecules
  • degranulation occurs
64
Q

What is the result of mast cell degranulation?

A

Acute inflammation and allergic responses

65
Q

IgE is important in host defense against…?

A

certain parasitic worms

66
Q

Structure of IgD

A

a monomer consisting of 2 δ chains and 2 κ or λ chains

67
Q

What is the level of IgD present in serum? Why?

A

Low due to susceptibility to proteolysis

68
Q

Where is most IgD found?

A

on the surface of B cells

69
Q

What is the role of IgD

A

involved in B cells activation in response to specific antigen

70
Q

Why are membrane bound immunoglobulin molecules unable to interact with intracellular signalling molecules?

A

Because they have very short cytoplasmic tails

71
Q

What 2 elements constitute the antigen binding receptor on B cells

A
  1. membrane bound immunoglobulin (mIg)
  2. Disulphide linked heterodimer Ig- α/Ig-β
    * not actually linked covalently but expressed in close proximity
72
Q

What is the purpose of the Ig- α/Ig-β heterodimer?

A

the cytoplasmic tails interact with intracellular signalling molecules like tyrosine kinases

73
Q

What are some of the immunoglobulin superfamily members?

A

antibody, Ig-α/Ig-β, the T cell receptor, Fc receptors, CD4, major histocompatibility complex molecules, and various cell adhesion molecules

74
Q

What is the immunoglobulin-fold domain structure?

A

110 amino acid residues arranged in antiparallel sheets of ß-pleated strands
-held together by intrachain disulphide bonds

75
Q

What are monoclonal antibodies?

A

derived from a single B cell clone

76
Q

What are monoclonal antibodies specific for

A

All specific for a single epitope on an antigen

77
Q

how can monoclonal antibodies be generated in vivo?

A

Fusing an immortal hybridoma cell with plasma cells that can have been exposed to antigen

the hybridomas of each plasma cell and cancer cell will produce a singel antibody

Immunology (19 decks)

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