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Immunohematology (Blood Bank and Serology) > Antigens and Antibodies > Flashcards

Antigens and Antibodies Flashcards

1
Q

Define immunogen.

A

macromolecules capable of triggering an adaptive immune response by inducing formation of antibodies or sensitized cells in an immunocompetent host

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2
Q

What is the action of an antigen?

A

reacts with antibody and/or sensitized cells but may not be able to invoke an immune response in the first place

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3
Q

What is the rule regarding the relationship between immunogens and antigens?

A

all immunogens are antigens, but not all antigens are immunogens

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4
Q

What is the ability of an antigen to stimulate a host response (immunogenicity) dependent on?

A

macromolecular size (molecular weight), chemical composition, molecular complexity, foreignness

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5
Q

What is the general rule regarding molecular weight and reactivity, and what is the minimum weight an antigen must be to be recognized?

A

the greater the molecular weight, the more potent the molecule is; 10,000 Daltons or more

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6
Q

What are considered the “best” materials for antigens to be made of?

A

proteins and polysaccharides

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7
Q

What makes carbohydrates less immunogenic than proteins?

A

the number of sugar units in carbohydrates are more limited than the number of amino acids in proteins

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8
Q

Can nucleic acids and lipids be immunogenic? If so, under what conditions?

A

yes, if they occur in conjunction with other substances

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9
Q

What makes proteins the ideal antigen material?

A

the variety of amino acids can arrange themselves into an enormous variety of 3D molecules

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10
Q

What makes synthetic polymers such as nylon and Teflon a good material for artificial medical appliances, such as heart valves?

A

they are made of up a few simple repeating units with no bending or folding within the molecule; therefore, they are non-immunogenic

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11
Q

What is the most common form of antigens composed of carbohydrates?

A

glycolipids or glycoproteins

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12
Q

Which blood group antigens are glycolipids?

A

A, B, H

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13
Q

Which blood group antigens are glycoproteins?

A

Rh and Lewis

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14
Q

What are epitopes?

A

small, molecular shapes or configurations on antigens that are actually recognized by antibodies or T-cells

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15
Q

What is another name for epitope?

A

determinant site

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16
Q

What is the relationship between molecular size and epitope number?

A

larger molecules may have more epitopes than smaller molecules; generally speaking, there is approximately one epitope for every increase of 10,000 Daltons in molecular weight

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17
Q

What is the dominant epitope?

A

the most exposed region of a molecule; the immune response is almost always directed against this particular area’s surface protein components

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18
Q

Are all of the epitopes on a single molecule the same?

A

they can be; also capable of having differing specificities

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19
Q

What is a linear epitope?

A

amino acids following one another on a single chain

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20
Q

What is a conformational epitope?

A

results from the folding of one or multiple chains, bringing certain amino acids from different segments into close proximity so they can be recognized together

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21
Q

What is the difference between B-cell (antibody) and T-cell recognition of antigens?

A

B-cells are capable of recognizing antigens in their original state; for T-cells, the antigen-presenting cell must degrade the immunogen into small peptides before T-cells can recognize it

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22
Q

What are haptens?

A

non-immunogenic materials that, when combined with a carrier, create new antigenic determinants; they are too small to be recognized on their own

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23
Q

Once antibody formation has been initiated, can a hapten react with that antibody even if it is not complexed?

A

yes, but it will not produce an agglutination or precipitation reaction; because a hapten has only one determinant site, it cannot form the cross-links with more than one antibody that are required to produce such a reaction

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24
Q

What are autoantigens?

A

antigens that belong to the host that do not produce an immune response under normal circumstances

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25
Q

What are alloantigens?

A

antigens from other member’s of the host’s species that are capable of eliciting immune responses; these play an important role in tissue transplants and blood transfusions

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26
Q

What are heteroantigens?

A

antigens from other species, such as animals, plants, or microorganisms

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27
Q

What are heterophile antigens?

A

heteroantigens that exist in unrelated plants or animals but are either identical or closely related in structure, so that antibody to one will react with the other (cross-reactivity)

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28
Q

What are adjuvants and how do they work?

A

Substances administered with an antigen that increase the immune response, such as metal salts made from aluminum or calcium. These complex with the antigen and increase its size to prevent a rapid escape from the tissues, which prolongs its existence in the area and increases the number of macrophages involved in the antigen processing

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29
Q

What are human leukocyte antigens (HLA)?

A

antigens found on all nucleated cells in the body that play a key role in the immune response

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30
Q

What is the major histocompatibility complex (MHC)?

A

the genes controlling the expression of human leukocyte antigens by coding for proteins that regulate the immune system

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31
Q

What is the main function of the MHC, and what specific conditions does it play a role in?

A

brings antigen to the cell surface for T-cell recognition; plays a role in graft rejection, transfusion reactions, and autoimmune diseases

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32
Q

Where are the MHC genes found and how are they categorized?

A

found on chromosome 6; Classes I, II, and III

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33
Q

Describe Class I MHC genes, including where the molecules are found.

A

coded for at three different loci termed A, B, and C; expressed on all nucleated cells

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34
Q

Describe Class II MHC genes, including where the molecules are found.

A

coded for in the D region with at least three different loci known as DR, DQ, and DP; found primarily on B-cells, activated T-cells, monocytes, macrophages, dendritic cells, and endothelium

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35
Q

Describe Class III MHC genes.

A

code for complement proteins

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36
Q

What kind of cells do Class I molecules present antigen to?

A

CD8 (cytotoxic) T-cells

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37
Q

What kind of cells involve Class II molecules in antigen recognition?

A

CD4 (helper) T-cells

38
Q

What is the main role of Class I molecules?

A

bind peptides that have been synthesized inside the cells by viruses, tumors, and intracellular pathogens and transport them to the plasma membrane where they can be recognized by the T-cells

39
Q

What is the main role of Class II molecules?

A

bind exogenous proteins that have been taken into the cells from the outside and degraded (ex., bacteria attacking cells from the outside)

40
Q

What is a haplotype?

A

the genes inherited at a particular chromosomal region

41
Q

How likely is it that two individuals will express the same human leukocyte antigens?

A

very low; due to the number of genes in the haplotype and the way in which they are inherited, an individual’s MHC type is about as unique as a fingerprint; this makes organ donation matching extremely difficult

42
Q

How would one go about resolving a discrepancy caused by cross-reactivity?

A

perform an adsorption on the serum to remove all but the antigen intended for testing

43
Q

What are immunoglobulins?

A

substances produced in response to an antigenic stimulation that are capable of specific interaction with the provoking antigen

44
Q

What property distinguishes and antibody from an immunoglobulin?

A

antibodies have specificity for a particular antigen

45
Q

Which heavy chain type is found in the IgG class?

A

gamma

46
Q

Which heavy chain type is found in the IgA class?

A

alpha

47
Q

Which heavy chain type is found in the IgM class?

A

mu

48
Q

Which heavy chain type is found in the IgD class?

A

delta

49
Q

Which heavy chain type is found in the IgE class?

A

epsilon

50
Q

What is the constant region of an immunoglobulin molecule associated with?

A

the biological properties that differ between each immunoglobulin class

51
Q

What is the variable region of an immunoglobulin molecule associated with?

A

provides the specificity for antigen binding

52
Q

What chemical property forms the connecting links within an immunoglobulin molecule?

A

disulfide bonds

53
Q

What is the function of the internal disulfide links found in the heavy and light chains of immunoglobulins?

A

they form loops in the peptide chains that compactly fold to form globular domains; these domains can in turn activate complement, bind antigen, and adhere to the monocyte surface, among other things

54
Q

Which immunoglobulin is found in the highest concentration in normal adults?

A

IgG

55
Q

What is the main function of IgG?

A

antibody capable of destroying bacteria, neutralizing viruses, and precipitation reactions; also make up som hemagglutinins and hemolysins

56
Q

Which immunoglobulin can cross the placenta?

A

IgG

57
Q

Which subclasses of IgG fix complement?

A

1-3; 4 does not

58
Q

Is IgG capable of opsonization?

A

yes

59
Q

Which immunoglobulin is the largest?

A

IgM; made up of five basic structural units in a circular arrangement (pentameter)

60
Q

How can the bonds holding an IgM molecule together be broken?

A

using 2-mercaptoethanol

61
Q

What is the name of the chains that hold the IgM pentameter together?

A

J (joining) chains

62
Q

Which immunoglobulin is associated with primary response?

A

IgM

63
Q

Which immunoglobulin is associated with secondary (anamnestic) response?

A

IgG

64
Q

What class of immunoglobulin is first produced by infants during development?

A

IgM

65
Q

What is the relationship between IgM and IgG?

A

synthesis of IgM decreases as concentration of IgG increases

66
Q

Which class of antibody is most often formed in response to Gram-negative bacteria, and what makes it so effective?

A

IgM; multiple binding sites

67
Q

What four components are characteristically IgM in nature?

A

heterophile antibody, rheumatoid factor, cold agglutinins, and hemagglutinins

68
Q

Can IgM activate complement?

A

yes, better than IgG

69
Q

What is the main immunoglobulin found in various body secretions, such as saliva, tears, sweat, and breast milk?

A

IgA, also known as secretory IgA

70
Q

What is the nature of the secretory component of IgA?

A

thought to protect the IgA dimer from enzyme destruction, and aid in transport across mucus membranes into secretions

71
Q

What is the main function of IgA?

A

binds antigen at portals of entry, and confers immunity from mother to baby through breast milk

72
Q

Which subclass is predominant?

A

IgA2

73
Q

Can IgA fix complement?

A

no

74
Q

Which immunoglobulin is found in the lowest concentration in the body?

A

IgE

75
Q

What makes IgE unique?

A

has an extra domain that is capable of binding with receptors on mast cells and basophils

76
Q

What effect does the attachment of IgE to mast cells and basophils have on the body in regards to allergic reactions?

A

mast cells and basophils release vasoactive amines/pharmacologic agents (histamine and heparin) which are important chemical mediators of allergic reactions; the interaction of IgE and active mast cells or basophils stimulates the development of an immediate physiologic response from life-threatening (anaphylaxis) to milder discomforts associated with allergies

77
Q

What role is IgE thought to have in the defense of parasitic infections?

A

recruits eosinophils to areas of infection

78
Q

Where are the major tissues that form IgE located?

A

respiratory and GI tract

79
Q

Can IgE fix complement?

A

no

80
Q

What is the synonym for IgE and what is important to remember about it?

A

reagin; this is NOT the same reagin as that found in syphilis

81
Q

Does IgE participate in agglutination or opsonization?

A

no

82
Q

Which immunoglobulin class was discovered in 1965 in a patient with multiple myeloma?

A

IgD

83
Q

Where is most IgD found?

A

on the surface of immunocompetent but unstimulated B-cells

84
Q

What is thought to be the role of IgD?

A

it is the second immunoglobulin to appear (and therefore may play a role in) B-cell activation, maturation, and differentiation

85
Q

Can IgD fix complement?

A

no

86
Q

What is the Fab fragment?

A

the site of antigen binding on an immunoglobulin (Fab = fragment antigen binding)

87
Q

Is the Fab fragment capable of causing agglutination or precipitation reactions?

A

no

88
Q

What is the Fc fragment?

A

the site of complement attachment/activation on an immunoglobulin (Fc = fragment crystallizable)

89
Q

Which proteolytic enzyme can be used to break apart IgG molecules into three equal parts?

A

papain

90
Q

Which proteolytic enzyme can be used to break apart IgG at the carboxy-terminal side of the interchain disulfide bonds?

A

pepsin

91
Q

What does a treatment of IgG with pepsin yield?

A

a single fragment weighing approximately 100,000 Daltons with all of the antigen-binding ability (known as Fab2), and an additional fragment known as Fc3

Immunohematology (Blood Bank and Serology) (15 decks)

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