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Immunology PY2 > Lecture 7&8: Antibody Structure & Function > Flashcards

Lecture 7&8: Antibody Structure & Function Flashcards

1
Q

what are antibodies aka immunoglobulins?

A

glycoproteins on the surface of B cells and secreted by plasma B cells

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2
Q

antibodies are present in which bodily fluids?

A

blood serum, secreted fluids such as saliva and breast milk

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3
Q

immunoglobulins activate which complement pathway?

A

classical

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4
Q

antibodies act as ___ to ___(increase or decrease) phagocytosis

A

opsonins; increase

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5
Q

antibodies do what to toxins and viruses (in general terms)

A

neutralize

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6
Q

antibodies function as ___ receptors for B cells

A

antigen

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7
Q

the membrane-bound antibodies on B cells have very ___ (long or short) tails; what is the significance of this?

A

short, so they are not able to interact with intracellular signalling molecules

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8
Q

to act as a B cell receptor, the membrane-bound immunoglobulin is joined to a ______ heterodimer by a disulphide linkage

A

Ig-a/Ig-B

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9
Q

what is the function of the hetrodimer that is joined to the immunoglobulin of the B cell receptor

A

they have longer tails that can interact with intracellular signalling molecules like tyrosine kinases

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10
Q

describe the structure of monomer antibodies

A

2 identical heavy chains and 2 identical light chains held together by disulphide and noncovalent bonds

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11
Q

what are the 5 classes of heavy chains for monomer antibodies?

A

a, circle with a squiggle on top (could be a delta or sigma), E, y, u)

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12
Q

what are the 2 classes of light chains in monomer antibodies?

A

K and upside down Y

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13
Q

in the immunoglobulin structure, globular domains of around 110 ____ are formed by intrachain disulphide bonds

A

amino acids

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14
Q

The V region of heavy and light chains is characterized by a ____ sepquence

A

variable amino acid

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15
Q

the C regions of heavy and light chains are characterized by a ____ sequence

A

relatively constant amino acid

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16
Q

Glycosylation of antibodies affects what aspects of their function?

A

their stability and interactions with other proteins

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17
Q

the antibodies of camels and lamas do not have which antibody chain?

A

light chain

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18
Q

do all vertebrates have antibodies?

A

no; things like the hagfish and lampreys have variable lymphocyte receptors (VLR) instead

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19
Q

how many V and C regions does each light chain have?

A

1C and 1 V

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20
Q

how many V and C regions do heavy chains have?

A

1V and 3-4 C regions

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21
Q

what chains form the antigen binding site?

A

the variable region domains at the amino-terminal portion of the heavy and light chains

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22
Q

there are 3 ____ regions within the V region that show even greater AA sequence variability and form the antigen binding site, while ____regions have much less variability

A

hypervariable; framework

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23
Q

what are the 3 hypervariable regions?

A

CDR1
CDR2
CDR3

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24
Q

in IgA, IgD, and IgG, what makes up the hinge-region between CH1 and CH2?

A

proline-rich amino acids

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25
Q

which antibodies do not have a hinge region? What do they have instead?

A

IgM and IgE; the CH2 domain has hinge-region-like properties

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26
Q

C regions at the carboxyl-terminal portion of heavy chains mediate ____ function

A

biological effector function

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27
Q

differences in the heavy chain constant regions determines what characteristics of the antibody?

A
  1. half life
  2. distribution
  3. complemenr-fixing
  4. Fc receptor binding
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28
Q

the carboxyl terminal domain of membrane-bound and secreted antibody is _____(the same/different) in terms of structure and function

A

different in both senses

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29
Q

t/f different classes of membrane-bound immunoglobulin molecules are expressed by B cells at different stages of their development

A

true

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30
Q

the enzymes ___ and ___ can cleave IgG molecules into specific fragments

A

papain and pepsin

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31
Q

what are the products of papain-mediated digestion of IgG molecules?

A

2 identical Fab fragments and 1 Fc fragment

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32
Q

what does FAB stand for?

A

fragment antigen-binding

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33
Q

what does Fc stand for?

A

fragment cystalizable

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34
Q

what are the products of pepsin-mediated digestion of an IgG molecule?

A

1 divalent F(ab’)2 fragment and 1 pFc’ fragment

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35
Q

what are the products of pepsin-mediated digestion of an IgG molecule?

A

1 divalent F(ab’)2 fragment and 1 pFc’ fragment

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36
Q

antibodies are ____; meaning they produce an immune response when injected into other species

A

immunogenic

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37
Q

isotypic epitopes are located in the ____ regions and they define the ____ and _____ within a species

A

heavy chain classes/subclasses and light chain types and subtypes

38
Q

allotypic epitopes are located in ___regions and may vary from ___ to ____

A

constant; from individual to individual

39
Q

idiotypic epitopes are located in the ____ regions and are defined by ____ that determine specificity

A

heavy and light chain variable regions (both hyper and framework); the unique AA sequences

40
Q

“determinant” is a synonym for ____ and means the same thing

A

epitope

41
Q

what is opsonization wrt antibodies (i.e. the reaction)?

A

interactions of antibodies with Fc receptors on phagocytes to promote phagocytosis

42
Q

what is antibody-dependent cell-mediated cytotoxicity (ADCC)?

A

antibody IgG acts as a receptor to enable recognition and killing target cells by NK cells with Fc receptors (CD16)

43
Q

what is trancytosis?

A

passage of antibodies across epithelial layers to deliver certain classes (mostly IgA) to mucosal surfaces

44
Q

the induction of mast cell degranulation is initiated by the ___ receptors of which antibody?

A

Fc of IgE

45
Q

what are 5 immunoglobulin effector functions?

A
  1. opsonization
  2. complement activation
  3. antibody-dependent cell-mediated cytotoxicity (ADCC)
  4. transcytosis
  5. mast cell degranulation
46
Q

what chains make up the IgG structure?

A

2 identical 50kDa y and 2 identical 25kDa k or upside down y chains

47
Q

there are ___ (#) subclasses of IgG in humans and each has its own unique biological properties

A

4

48
Q

what is the most abundant antibody in serum and extravascular spaces?

A

IgG

49
Q

what are the functions of IgG?

A
  1. neutralizes viruses/toxins
  2. opsonizes microbes
  3. activates classical complement pathway
    ADCC
50
Q

does IgG cross the placenta?

A

yes

51
Q

IgM is a monomer when expressed ____ and a pentamer with a J chain when ___

A

on surface of B cells; secreted by plasma B cells

52
Q

what chains make up the monomer structure of IgM?

A

2 u chains and 2 k or upside down y)

53
Q

how many antigen-binding sites on pentameric IgM are able to physically interact with large antigens?

A

5-10

54
Q

what antibody is the first made by newborns and is involved in teh primary immune response?

A

IgM

55
Q

IgM is an efficient ___ of particulate antigens and an activator of the ___ complement pathway

A

agglutinator; classical

56
Q

IgM is found in ____ (high or low) concentration in the fluid between cells; why?

A

low; its large size prevents easy movement across blood vessel walls

57
Q

what allows the IgM pentamer to be transported across epithelial mucosa?

A

the J chain

58
Q

where is IgA a monomer? Where is it a dimer?

A

monomer in the blood and a dimer in mucosal secretions

59
Q

what chains make IgA?

A

2 a chains and 2 k or upside down y chains

60
Q

the dimer form of IgA also contains what 2 extra things?

A

a J chain and a secretatory component

61
Q

dimeric IgA is formed by plasma cells by the addition of a ____

A

J chain

62
Q

at what stage is the secretatory component added to the dimeric IgA?

A

during its passage through glandular epithelial cells

63
Q

what is the function of the secretatory component added to the IgA?

A

protects IgA from proteolysis

64
Q

what is the main function of dimeric IgA?

A

defends mucosal surfaces from microbial attack by inhibiting pathogen adherence

65
Q

IgA-antigen complexes are trapped in ____ and eliminated by ___

A

mucus; mechanical action

66
Q

IgA is present in breast milk, what is the function of this?

A

provides newborn with mucosal immunity to environmental pathogens

67
Q

what chains make up the IgE molecule?

A

2 E chains and 2 k or upside down chains

68
Q

a ____(small or large) amount of IgE is found in the blood; why?

A

small; only really present in high amounts when there is an allergic response or parasitic infection

69
Q

what is the main function of IgE? How does it do this?

A

mast cell and bosophil degranulation. Binds high affinity FcE receptors on these cells and cross link with other IgE molecules

70
Q

mast cell degranulation caused by IgE leads to what?

A

acute inflammation, atopic (Type 1) allergic responses

71
Q

IgE has an important role in host defence against what types of infections?

A

parasites, especially certain species of parasitic worms

72
Q

what chains make up the IgD?

A

2 delta chains and 2 k or lambda chains

73
Q

the amount of IgD is very ___(low/high) in the blood, why?

A

low bc it is very susceptible to proteolysis

74
Q

where can you find most of the IgD in the body?

A

on the surface of B cells

75
Q

what is the function of IgD?

A

involved in B cell activation in response to specific antigen

76
Q

molecules that are associated with immune function and have what structure are considered members of the “immunoglobulin superfamily”?

A

immunoglobulin-fold domain structure (i.e. 110 AA arranged in antiparallel sheets of B pleated strands)

77
Q

Give 7 examples of members of the Ig superfamily

A
  1. Ig-a/Ig-B
  2. T cell receptor
  3. Fc receptors
  4. CD4
  5. MHC
  6. antibody
  7. various cell-adhesion molecules
78
Q

how is it believed that the Ig superfamily of genes originated?

A

through mutation and duplication from a single primordial gene encoding a polypeptide of 110 amino acids

79
Q

where are MABs derived from? What is the implication of this?

A

from a single B cell clone; this means they are specific for a single epitope rather than for polyclonal AB that are made by many different B cells and so many bind different epitopes

80
Q

MABs are produced by what types of cells?

A

immortal hydridoma cells created by fusing an antigen-specific B cell with a cancerous myeloma cell

81
Q

the hybrid cells used in making MABs are secreted by ____

A

growth in special tissue culture medium that allows only the hybridoma cells to grow

82
Q

hybridoma clones that produce a MAB with the desired antigenic specificity are prepared by _____ for use as diagnostic, imaging, and therapeutic agents

A

propagating them in tissue culture using bioreactors

83
Q

Sometimes, AB can be found on the surface of mast cells, why is this?

A

mast cells have a Fc1 receptor

84
Q

t/f the structure of AB is called a heterotertromer

A

true

85
Q

VLRs are similar to AB in struture and function, but not in ____

A

sequence

86
Q

VLRs are expressed in what type of vertebrates?

A

jawless

87
Q

VLR are made of what? What are they more similar to (compared to AB)?

A

leucine-rich repeats; more similar to TLRs and NLRs

88
Q

t/f VLRs can be membrane-bound or secreted

A

t

89
Q

what is the purpose of the hinge region?

A

allows for different size and shaped antigens

90
Q

Naive B cells have ____ and ___ antibodies on their surface and then once they switch to plasma cells, they secrete ____, ___ antibodies etc.

A

IgM and IgD; IgA, IgG

91
Q

where does pepsin cleave the antibody?

A

right below the disulphide bonds between the 2 heavy chains

92
Q

where does papain cleave the antibody

A

right above the disulphide bond of the heavy chains

Immunology PY2 (20 decks)

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