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Blake + Ashton's Immunology RUSVM Test 2 > Antibodies (Abs) or Immunoglobulins (Igs) > Flashcards

Antibodies (Abs) or Immunoglobulins (Igs) Flashcards

1
Q

What kind of proteins are antibodies? What produces them?

A

They are plasma glycoproteins produced by plasma cells (Ab-producing cells of B cell lineage) in response to antigens.

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2
Q

In which phases do antibodies bind to their specific antigens?

A

In both the recognition phase (as membrane Igs [BCRs]) and the effector phase (as secreted Abs) of HUMORAL IMMUNITY.

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3
Q

What percentage of total plasma protein is secreted Abs?

A

~20% of total plasma protein.

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4
Q

In addition to plasma, secreted Abs are also found where?

A

In mucosal secretions and the interstitial fluid of tissues.

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5
Q

T or F?

Antibodies are beta-globulins.

A

FALSE.

Antibodies are gamma-globulins.

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6
Q

What percentage of IgG is carbohydrate?

A

3-4%

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7
Q

What percentage of IgA, IgM, IgD, and IgE is carbohydrate.

A

10-18%

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8
Q

T or F?

The oligosaccharide side chains of Igs are usually attached to the CH2 or CH3 domains of the Ig light chain.

A

FALSE.

The oligosaccharide side chains of Igs are usually attached to the CH2 or CH3 domains of the Ig HEAVY chain.

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9
Q

These structures possess subterminal galactose and terminal neuraminic acid…

A

The oligosaccharide side chains of Igs.

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10
Q

What does the half-life of Igs in the circulation depend on?

A

The half-life of Igs in the circulation depends on the status of the oligosaccharide side chains.

For example, When ABs in the circulation have the neuraminic acid removed by the enzyme neuraminidase, the now terminal galactose binds to a receptor on liver cells, triggering endocytosis of the Ig –> the Ig is then degraded by the proteolytic enzymes in the lysosomes of the cell.

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11
Q

How many polypeptide chains do Ig molecules consist of? How many are light and how many are heavy?

A

4: two identical light (L) chains and two identical heavy (H) chains.

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12
Q

What are the polypeptide chains of the Ig molecules held together by?

A

They are held together by noncovalent AND covalent inter/intrachain disulfide bonds.

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13
Q

T or F?

Each chain of the Ig molecule consists of a variable (V) and a constant (C) region.

A

TRUE

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14
Q

What is a “domain” in the Ig context?

A

It is a 3-dimensionally folded repeating segment - a loop of about 60 AAs around an intrachain S-S bond.

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15
Q

T or F?

An L chain consists of one variable (VL) and one constant (CL) domain.

A

TRUE.

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16
Q

T or F?

Most H chains consist of one variable (VH) and one constant (CH) domain.

A

FALSE.

Most H chains consist of one variable (VH) and 3-4 constant (CH) domains.

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17
Q

IgA, IgG, and IgD possess how many CH domains? What are they called?

A

3 CH domains: CH1, CH2 and CH3.

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18
Q

IgE and IgM possess how many CH domains? What are they called?

A

4 CH domains: CH1, CH2, CH3, and CH4.

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19
Q

What is a hinge region?

A

It is a proline-rich region between the CH1 and CH2 domains.

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20
Q

What does the hinge region do to the structure of the Ig molecule?

A

The hinge region confers segmental flexibility on the Ig molecule, which allows the two antigen combining sites (Fabs) to simultaneously bind 2 epitopes separated by varying distances.

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21
Q

T or F?

All Igs have hinge regions.

A

FALSE.

IgE and IgM do not possess hinge regions.

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22
Q

What does it mean that Ig molecules are ‘bifunctional’ in nature?

A

To say that Ig molecules are bifunctional is to say that: the antigen recognition functions AND the effector functions of Ig molecules are spatially separated from each other.

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23
Q

What two enzymes did scientists use to determine that Ig molecules are bifunctional in nature? What do these enzymes do?

A

Papain and pepsin…

Papain: cleaves IgG ABOVE the S-S bond at the hinge region, which produces 2 antigen-binding fragments (bivalent); The Fab region, which stands for fragment antigen binding; Fc, which stands for fragment crystallizable.

Pepsin: Cleaves IgG BELOW the S-S bond at the hinge region.

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24
Q

T or F?

The hinge region and interchain disulfide bonds are retained in a F(ab’)2 molecule, but the Fc fragment is degraded after pepsin acts upon an IgG.

If so, why? If not, why?

A

This is TRUE because pepsin will cleave BELOW the S-S bond at the hinge region.

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25
Q

T or F?

Fab and F(ab’)2 binding to antigens will always activate Fc-dependent effector functions.

A

FALSE.

Fab and F(ab’)2 can bind to antigens without activating Fc-dependent effector functions.

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26
Q

T or F?

The Fc piece of an antibody can bind to Fc receptors on various cells.

A

TRUE.

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27
Q

How many AAs are in an Ig molecule’s light chain?

A

Each Ig molecule possesses two identical light chains; each of which consists of 200-250 AAs linked by S-S bonds to a heavy chain.

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28
Q

How many AAs are in a light chain’s variable region (VL)?

A

The light chain’s variable region consists of the first 100-110 AAs.

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29
Q

How many kilodaltons are in the light chains?

A

~ 24 kD

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30
Q

How many light chain isotypes (classes) are there? What are they called? What is different between each?

A

There are two isotypes of light chains; kappa and lambda. They differ by the amino acids in their CL regions.

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31
Q

T or F?

A given Ig molecule ALWAYS contains 2 kappa OR 2 lambda light chains, but NEVER a mixture of the two (1 each).

A

TRUE.

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32
Q

T or F?

The proportion of kappa to lambda chains in Ig molecules varies from species to species.

A

TRUE.

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33
Q

Do the CL regions of light chains have effector functions?

A

No.

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34
Q

What is the difference in function between kappa-containing Igs and lambda-containing Igs?

A

The premise is false; there are NO known differences in function between kappa-containing Igs and lambda-containing Igs.

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35
Q

How many times does Gyimah open his eyes while lecturing?

A

Only twice.

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36
Q

How much does a heavy chain weigh?

A

~55-70 kDs.

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37
Q

How many AAs are there in each of the two heavy chains of an Ig molecule?

A

~450-600 AAs.

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38
Q

How many AAs are in an Ig heavy chain’s variable region?

A

An Ig heavy chain’s variable region is the amino-terminal first 100-110 AAs.

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39
Q

T or F?

Heavy chains are divided into isotypes AND subisotypes based on the amino acid sequence of the variable region (VH).

A

FALSE.

Heavy chains are divided into isotypes AND subisotypes based on the amino acid sequence of the CONSTANT REGION (CH).

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40
Q

T or F?

Different CH isotypes and associated Fc regions (CH2, CH3) perform DISTINCT effector functions.

A

TRUE.

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41
Q

What are two examples of CH-Fc effector functions?

A

Complement activation (IgG and IgM) and opsonization (IgG).

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42
Q

What is another name for the hypervariable regions?

A

Paratopes.

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43
Q

Hypervariable regions (3) are sites within the __ and __ chains, where the amino acid sequences are highly variable.

A

VL and VH.

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44
Q

How many AA residues long are the hypervariable regions?

A

~5-10 amino acid residues long.

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45
Q

What is a framework region? What do they do?

A

Framework regions exist between each hypervariable region. They have a relatively constant AA sequence and provide the molecular scaffold for V-region structure.

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46
Q

The 3 hypervariable regions of a light chain and the 3 hypervariable regions of a heavy chain form the _________.

A

antigen-binding site.

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47
Q

What are complementarity-determining regions (CDRs)?

A

Because the hypervariable regions form a surface that is complementary to the epitopes of the bound antigen, they are also referred to as CDRs (CDR1, CDR2, and CDR3).

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48
Q

Which CDR molecule is the most variable of all the CDRs? What does this imply?

A

The CDR3 of both the VL and VH segments are the most variable of the CDRs (a result of junctional diversity). Thus, the most extensive contact with antigen occurs with CDR3.

49
Q

Antigen-antibody interaction is characterized by what kind of binding?

A

noncovalent, reversible binding.

50
Q

Name the 4 kinds of bonds/interactions that contribute to antigen-antibody binding.

A

1) Ionic bonds (electrostatic interactions).
2) Van der Waals forces.
3) Hydrogen bonds.
4) Hydrophobic interactions.

51
Q

T or F?

Affinity refers to the strength of binding between 1 Fab fragment of Ab and an epitope of an antigen.

A

TRUE.

52
Q

What causes the increase in the affinity of Abs? When does this occur?

A

Point mutations in the rearranged V, J, and D genes. This occurs during the course of the humoral immune response.

53
Q

What is avidity?

A

This is the sum total of the strength of binding of two molecules, such as antibody and antigen.

54
Q

T or F?

Affinity is greater than the avidity of any given antigen-binding site.

A

FALSE.

Avidity is much greater than the affinity of any given antigen-binding site because avidity takes into consideration the binding of Fabs to all the available epitopes.

55
Q

Can antibodies act as antigens?

A

Yes,; being glycoproteins, Abs can act as antigens when introduced into a foreign host, inducing the production of anti-antibodies.

56
Q

Isotypes (subisotypes) refers to the amino acid differences in the ___ and ___ regions that distinguish each immunoglobulin class and subclass.

A

CL and CH.

57
Q

T or F?

Allotypes are characterized by a few amino acid differences of Ig CL and VL regions.

A

FALSE.

Allotypes are characterized by a few amino acid differences of Ig CL and CH regions.

58
Q

T or F?

Within a species, the genes that code for the CL and CH chains are polymorphic, hence individual members can express different alleles.

A

TRUE.

59
Q

What kind of immunoglobulin variability characteristic is used to establish paternity and blood stain origins?

A

Allotypic differences.

60
Q

Idiotypes are characterized by the unique combination of amino acids in the ______ regions of the ____ and ____ chains.

A

Variable regions of the light and heavy chains.

61
Q

T or F?

Each idiotype is unique for the antigen specific antibody produced by a clone of B cells.

A

TRUE.

62
Q

What is the primary function of an antibody molecule?

A

To bind antigen.

63
Q

When antibodies bind antigens, are the effects direct or indirect?

A

BOTH, but most of the time it does NOT elicit a direct effect.

64
Q

Most of the time, the effector functions of antibodies are initiated only when antibodies bind to their specific antigens and engage other _____ ______ or cells.

What are some examples of these?

A

Effector molecules or cells; complement proteins, neutrophils, etc…

65
Q

Which portion of the which chain mediates effector functions of immunoglobulins most of the time?

A

The Fc portion of the heavy chain.

66
Q

T or F?

Neutralization is the ONLY function of Igs mediated EXCLUSIVELY by Fab binding of antigen and does NOT require participation of the CH regions.

A

TRUE.

67
Q

How can some bacteria prevent the Fc portion from carrying out its effector functions?

A

Some bacteria produce proteins (eg, protein A of S. aureus, see page 148) that either bind to or proteolytically cleave the Fc portion, hence preventing it from carrying out its effector functions.

68
Q

T or F?

Fc receptors are signaling receptors specific for antibodies of different classes.

A

TRUE.

Some of these are Fc(gamma)Rs, Fc(alpha)Rs, and Fc(epsilon)Rs.

69
Q

T or F?

An individual cell may express different FcRs for different antibody classes.

A

TRUE.

Like eosinophils, for example.

70
Q

What is the major Ig in serum and is the major Ig produced in the secondary immune response? How long does it last in the body compared to the other Igs?

A

IgG. It is the longest lasting Ig in the body (it has the longest half-life).

71
Q

Where is IgG found?

A

In blood, tissue spaces and extravascular spaces.

72
Q

Which Fc receptors bind the Fc portion of IgG? How many are there?

A

Fcy receptors; there are three: named FcyRI-III.

There are two types of FcyRII: A and B.

73
Q

Where is FcyRIIB found? What does it express/what does it do?

A

FcyRIIB is found on B cells and expresses an inhibition motif; when cross-linked to the BCR, it delivers inhibitory signals to the B cell, blocking B cell activation.

74
Q

Why do FcyRs on phagocytes interact more efficiently with IgG bound to antigen?

A

Because the IgG forms multivvalent arrays and are bond with much higher avidity than are free circulating IgGs.

75
Q

T or F?

When FcyRs on phagocytes interact with antigen bound-IgG it triggers engulfment and delivery of signals that enhance mirobicidal activities of the phagocyte.

A

TRUE.

76
Q

What are the functions of IgG? What is a special characteristic of IgG?

A

1) Opsonization. 2) Neutralization of viruses and microbial toxins. 3) Complementation activation.

IgG is the only antibody to cross the placenta in some species; only its Fc portion binds to receptors on the surface of placental cells.

77
Q

What is the first Ig class produced both during the development of B cells AND during the primary immune response?

A

IgM.

78
Q

In serum, IgM iis a pentamer with 5 ____ units plus 1 molecule of _____ chain.

A

H2L2; J (joining) chain.

79
Q

T or F?

Because the pentamer of IgM has 10 Fabs, it is the least efficient Ig in agglutinating particulate matter.

A

FALSE.

Because the pentamer of IgM has 10 Fabs, it is the MOST efficient Ig in agglutinating particulate matter.

80
Q

T or F?

IgM has the lowest avidity of the Igs.

Why?

A

FALSE.

IgM has the HIGHEST avidity of the Igs; its interaction with antigen can involve all 10 of its binding sites.

81
Q

Why is IgM confined to the blood vascular system? What is the implication of this fact?

A

IgM is so large that it is confined to the blood vascular system and, consequently, is of little importance in conferring protection in tissue fluids or body secretions.

82
Q

Because IgM’s pentamer has ____ Fabs, it is the ______(most/least) efficient Ig in agglutination, complement activation, etc…

A

10; most efficient.

83
Q

Monomeric IgM functions as an antigen receptor on which kinds of cells?

A

Naive B cells - it is a BCR.

84
Q

T or F?

IgM will neutralize viruses and microbial toxins; agglutination; and complement activation.

A

TRUE.

85
Q

T or F?

IgM is an opsonin.

A

FALSE.

IgM is NOT an opsonin because phagocytes do not possess FcuRs; however, IgM is a potent activator of the complement system, generating the opsonins C3b, iC3b, and C4b.

86
Q

Which immunoglobulin is the predominant Ig produced by the fetus?

A

IgM.

87
Q

Elevated IgM level in the blood of a newborn is indicative of what?

A

Transplacental infection.

88
Q

What is the most abundant Ig in the body? Where is it produced?

A

IgA synthesis occurs mainly in mucosal lymphoid tissues, especially the GI and respiratory tracts, hence, it is the most abundant Ig in the body.

89
Q

What are the two forms of IgA? What are the differences in structure between these two?

A

The two forms of IgA are…

Serum IgA - produced most as a monomer.

Secretory IgA (sIgA) - it is a dimer plus a joining chain and secretory component.

90
Q

T or F?

The secretory component of sIgA is a polypeptide synthesized by epithelial cells, which helps transport IgA to the mucosal surface in addition to protecting IgA from proteolytic degradation.

A

TRUE.

91
Q

Which Ig is the major effector Ig at the mucosal level and is also the most predominant Ig in saliva/tears/milk?

A

IgA.

92
Q

Which Ig protects mucosal surfaces by preventing the attachment of microorganisms and microbial toxins to mucous membranes?

A

IgA.

93
Q

Is serum IgA a component of systemic humoral immunity?

A

Yes, but because of its low concentration in serum, IgA is a minor component of systemic humoral immunity when compared with IgG and IgM…. But, is still a component nevertheless.

94
Q

How many CH domains does IgE possess?

A

Similar to IgM, IgE possess 4 CH domains.

95
Q

IgE’s Fc portion binds to what receptors on which cells?

A

IgE’s Fc portion binds to Fc(epsilon)Rs on mast cells, basophils and eosinophils.

96
Q

T or F?

IgE is heat-labile at 56C for 30mins, whereas other Ig isotypes are heat-stabile at 56C.

A

TRUE.

97
Q

Which Ig mediates immediate hypersensitivity (anaphylaxis) by causing release of mediators upon exposure to antigen.

In other words, which Ig is referred to as the “reaginic antibody”?

A

IgE.

98
Q

Which Ig will defend against some helminth infestations by causing the release of enzymes from eosinophils onto the parasite?

A

Ig3

(see page 153).

99
Q

What is IgD’s only known function?

A

Its only known function is as an antigen receptor (together with IgM) on naive B cells.

100
Q

Activation of B cells provokes the loss of which membrane Igs?

A

Membrane IgDs.

Remember, daughter cells do not express IgD

101
Q

T or F?

Unlike IgE, IgD is not heat-labile at 56C for 30 mins.

A

FALSE.

Like IgE, IgD is heat-labile at 56C for 30 mins.

102
Q

T or F?

Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC) is the killing of antibody-coated target cells by nonspecific cells with Fc receptors that recognize the Fc region of the bound antibody.

A

TRUE.

103
Q

What cells mediated most ADCC? What do these cells have on their surface?

A

Most ADCC is mediated by NK cells that have FcyRIII (CD16) on their surface.

104
Q

Which leukocyte(s) express FcyRs and kill target cells via IgG-mediated ADCC?

A

Macrophages and neutrophils.

105
Q

Which leukocyte(s) express Fc(epsilon)Rs and kill helminth parasites via IgE-mediated ADCC?

A

Eosinophils.

106
Q

Which is the heaviest Ig?

A

IgM

107
Q

Which Ig is the highest percentage of serum Igs?

A

IgG

108
Q

Which Ig has the shortest serum half-life? The longest?

A

Serum IgE and IgD have the shortest half-lives, while IgG has the longest half-life.

109
Q

Which is the only Ig that functions as an opsonin?

A

IgG

110
Q

Which Ig has the highest valency?

A

IgM (10 Fabs).

111
Q

What does it mean for an antibody to be polyclonal?

A

It consists of various classes, specificities, and affinities for the different epitopes on the antigen.

112
Q

T or F?

Antibodies that arise from a single clone of cells are heterogenous and are directed against many epitopes; such antibodies are called monoclonal antibodies (mAbs).

A

FALSE.

Antibodies that arise from a single clone of cells are HOMOGENOUS and are directed against only ONE epitope; such antibodies are called monoclonal antibodies (mAbs).

113
Q

The technique of B cell/myeloma fusion is known as the _______ technique. What will the fusion of these cells produce?

A

This is called the hybridoma technique and will result in the production of B cell lines that will grow in cell culture, yet maintain the ability to produce antibodies.

114
Q

Monospecific Abs can be produced in cell culture by…

A

Isolating a single, antibody-producing B lymphocyte and letting it grow in cell culture.

115
Q

The addition of what to B Cells and myeloma cells will cause cell fusion?

A

polyethylene glycol.

116
Q

What must the culture medium contain in order to grow the fused B cell + myeloma cell? Will unfused cells survive in this medium?

A

hypoxanthine-aminopterin-thymidine (HAT); no.

117
Q

Where can hybridoma cells be grown in? What will they provide? And where is this substance found?

A

Hybridoma cells can be grown in the abdomen of mice, providing relatively large supplies of antibodies present in ascitic fluid; or they can be frozen and stored to be reused later.

118
Q

What are the clinical uses of mAbs?

A

1- anticancer remedies.
2- HLA detection.
3- Pregnancy determination.
4- As a substance that can remove drugs from the body more quickly than if the body worked alone.
5- Serotyping of viruses + bacteria.
6- monoclonal fluorescent antibody technique.
7- Detection and/or quantification of antibodies (indirect ELISA).
8- Separate mixtures from one another by directing mAbs against specific cell markers.

Blake + Ashton's Immunology RUSVM Test 2 (8 decks)

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