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Immunology PY2 > Lecture 9: Antigen Structure & Interactions with Antibody > Flashcards

Lecture 9: Antigen Structure & Interactions with Antibody Flashcards

1
Q

what is the function of an immunogen?

A

generates either a humoral or cellular immune response

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2
Q

what is the function of an antigen?

A

reacts with antigen receptors whether or not it is able to create an immune response

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3
Q

Antigen binding to its receptor may or may not lead to an immune response, why might a response not happen?

A

certain small molecules react with preformed antibodies but are not capable of stimulating a specific immune response unless complexed with a larger protein

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4
Q

what are 4 types of antigens?

A
  1. proteins
  2. polysaccharides
  3. lipids
  4. nucleic acids
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5
Q

what type of antigens are the most potent?

A

proteins

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6
Q

what are the second most potent antigens?

A

polysaccharides

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7
Q

lipids and nucleic acids are not usually immunogenic unless ____

A

they are complexed with proteins or polysaccharides

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8
Q

proteins and polysaccharides activate ____ cells and induce ____ responses

A

B cells and immune presponses

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9
Q

proteins and glycolipids and lipids presented by CD1 induce ____ cell responses

A

T cell

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10
Q

what are 4 important properties of antigen?

A
  1. foreigness
  2. molecular size
  3. chemical complexity & composition
  4. susceptibility to processing and presentation
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11
Q

explain the “foreigness” property of antigens

A

antigens need to be recognized as non-self to create an immune response

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12
Q

antigens with a molecular size greater than ___kDa are optimal for immunogenicity and those less than ___kDa are generally poor antigens

A

100; 5-10

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13
Q

explain the role of chemical complexity and composition of antigens

A

the more complex an antigen, the greater its immunogenicity

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14
Q

describe the difference in immunogenicity between homopolymers and copolymers

A

homopolymers, regardless of their size, tend to lack immunogenicity while copolymers of sufficient size are immunogenic

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15
Q

what type of antigens would not be susceptible to processing and presentation to stimulate T cells (making them poorly immunogenic)?

A

macromolecules

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16
Q

what are 4 biological factors affecting immunogenicity?

A
  1. genotype of recipient
  2. immunogen dosage
  3. route of administration
  4. adjuvants
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17
Q

how does the genotype of the recipient affects immunogenicity?

A

some people may fail to mount an effective immune response to certain antigens while others may mount a more intense response because of their gene expression profile

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18
Q

how can immunogen dosage affect immunogenicity?

A

too much or too little antigen will fail to induce an immune response (insufficient activation or tolerance); repeated doses of immunogen will increase the strength of the immune response

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19
Q

how does route of administration affect immunogenicity?

A

intradermal and SQ are superior to the oral route

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20
Q

how do adjuvants affect immunogenicity?

A

they are substances that when mixed with antigen, increase their immunogenicity

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21
Q

what are the 4 ways adjuvants can increase the immunogenicity of antigen?

A
  1. prolong antigen persistence
  2. enhance the costimulatory signal
  3. increase local inflammation, resulting in macrophage activation and antigen presentation
  4. stimulate the nonspecific proliferation of lymphocytes
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22
Q

what are epitopes?

A

immunologically active regions of an immunogen

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23
Q

antigen receptors on lymphocytes recognize discrete sites on antigens called ____ or ____

A

epitopes or antigenic determinants

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24
Q

does the antigen recognition of B and T cells involve the same epitopes?

A

no; they are fundamentally different

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25
Q

in B cells, antibodies recognize native antigens by binding to epitopes that are ___ and ____

A

accessible and hydrophobic

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26
Q

in B cells, the antibodies may interact with ___sequences of AA or with ____ or ___ type epitopes

A

linear; nonsequential or conformational

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27
Q

how do antigens and antibodies bind to each other in B cells?

A

by weal noncovalent interactions due to complementarity in shape between epitope and antigen-binding site of the antibody

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28
Q

in B cells, most antibodies raised against a globular protein recognize surface structures that depend on the ____ of the native protein

A

conformation

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29
Q

B cell epitopes tend to be found in the ____ regions of an immunogen

A

flexible

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30
Q

in B cells; a large & complex protein antigen has many possible epitopes, but the _____ are the regions that are most accessible to antibody

A

immunodominant antigenic determinants

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31
Q

a ____ (large or small) antigen is more likely to bear a number of structurally distinct antigenic determinants

A

large

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32
Q

T cells only recognize peptides complexed with _____ on the surface of APC and other nucleated cells

A

self MHC

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33
Q

where are T cell epitopes typically located?

A

internally

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34
Q

T cell epitopes typically contain ____peptide sequences revealed by antigen processing

A

amphipathic

35
Q

in T cell epitopes, the hydrophobic sequnces interact with ____ and hydrophilic sequences interact with ___

A

MHC; T cell receptor

36
Q

what determines immunodominance of T cell epitopes?

A

the ability to interact with the MHC of a given individual

37
Q

certain T cells can also recognize ____ and ___ presented by CD1 as antigen

A

lipids and glycolipids

38
Q

what is the function of mitogens?

A

capable of activating many clones of B or T cells, irrespective of their antigenic specificity

39
Q

mitogens are known as ___ activator s

A

polyclonal

40
Q

what mitogens preferentially activate T cells?

A

lectin concanavalin A

41
Q

what mitogens preferentially activate B cells?

A

LPS

42
Q

what is an example of a superantigen?

A

staphylococcal enterotoxins

43
Q

what is the function of superantigens?

A

activate a large number of T helper cells by cross-linking their T cell receptors with any MHC class 2 of an APC

44
Q

superantigens are extremely potent ___

A

T cell mitogens

45
Q

what type of bonding is involved in antigen-antibody reactions (4 types of noncovalent)

A
  1. ionic or electrostatic
  2. hydrogen
  3. hydrophobic
  4. Van der Waals
46
Q

exclusion of water molecules at the site of antigen-antibody interaction ____ (increases/decreases) the magnitude of the weal atomic forces

A

increases

47
Q

do the antigen-antibody reactions ever involve covalent binding? What is the significance of this?

A

no; this means their bonds are readily reversible

48
Q

what is affinity?

A

the strength of the sum total of noncovalent interactions between a single epitope and an antigen-binding site of an antibody

49
Q

what is avidity?

A

the overall strength of binding between a multivalent antibody and a multivalent antigen

50
Q

when does cross-reactivity happen?

A

when antibodies in a polyclonal antibody preparation raised against one antigen cross-react with a partially related antigen that has one or more identical or similar epitopes

51
Q

what are precipitation reactions?

A

mixing an antigen in aqueous solution with specific antibodies in the correct ratio results in the formation of visible precipitates

52
Q

the antibodies involved in precipitation reactions are called ____

A

precipitins

53
Q

what is the structure of the precipitates from the precipitation reaction?

A

3D lattice structure

54
Q

how are the precipitates formed in precipitation reactions?

A

by cross-linking of multivalent soluble antigen with divalent (IgG) or pentameric (IgM) antibody molecules

55
Q

t/f no precipitates are formed in there is an excess of antibody and or antigen

A

t

56
Q

t/f precipitation reactions can be visualized in semi-solid media such as agarose gel

A

t

57
Q

what are agglutination reactions?

A

cross-linking of particulate multivalent antigens such as cells by antibodies that are at least divalent leads to agglutination of particles

58
Q

the antibodies involved in agglutination reactions are called ___

A

agglutinins

59
Q

antibody excess that inhibits agglutination is called the ___ effect

A

prozone

60
Q

during agglutination, sufficient links must be formed at the greatest possible distance to overcome ____ by particles with the same charge, such as RBC

A

mutual repulsion

61
Q

which is a better agglutinin and why: IgM or IgG?

A

IgM because it spreads antigen the greatest possible distnace to overcome repulsion due to pentameric structure

62
Q

what can be detected by Enzyme-linked Immunosorbant Assay (ELISA)?

A

specific antibody (indirect ELISA) or antigen (sandwich ELISA)

63
Q

explain how an indirect ELISA works

A
  1. antigen is absorbed to teh wells of a plastic plate in a monomolecular layer
  2. excess antigen is removed by washing & irrelevant protein is used to block remaining free sites on the plastic
  3. excess blocking protein is removed by washing and the patient’s serum is added to the well
  4. after another wash, the enzyme-conjugated anti-immunoglobulin (isotype-specific) is added
  5. unbound antibody is removed by washing and the colourless substrate is added
  6. the colour recation generated by the enzyme is quantified by absorbance using an automated plate reader
64
Q

in sandwich ELISA, a ____ is absorbed to the well before the antigen-containing preparation is added

A

capture antibody

65
Q

what is a ELISPOT assay?

A

a modification of ELISA that allows measurement of molecules secreted by individual cells

66
Q

how is an ELISPOT assay performed?

A

1wells are coated with detection antibody

  1. washed, and blocked
  2. cell population added and cultured to allow secretion of molecule of interest
  3. cells washed away
  4. detection antibody added
  5. washing & substrate addition
67
Q

what is the purpose of Immunofluorescence reactions?

A

antigen-antibody complexes can be visualized under UV light if fluorescent dyes are first coupled to the antibody molecules

68
Q

what is immunofluorescence used to assess?

A

antigen distribution on cells or tissues

69
Q

what is the direct method of immunofluorescence?

A

the primary antibody is tagged with the fluorochrome

70
Q

what is the indirect method for immunofluorescence?

A
  1. unlabelled primary antibody bound to the substrate is visualized with a fluorochrome-conjugated anti-immunoglobulin preparation that is specific for the isotype of the primary antibody
  2. Alternatively: use fluorochrome-labeled protein A, which binds the Fc region of certain immunoglobulin subclasses
71
Q

what are 2 advantages of the indirect method for immunofluorescence?

A
  1. increased sensitivity bc several fluorescent secondary antibodies bind to each primary antibody
  2. simplicity bc each primary antibody does not need to be coupled to a fluorochrome
72
Q

in flow cytometry using fluorochrome-labeled antibodies, the forward & side scatter of light gives an indication of cell ____ and ____ respectively and this is used for gating

A

forward: cell size
side: complexity

73
Q

what shape antigens can bind to B cells? T cell?

A

B cells: 3D

T cells: linear complexed with MHC

74
Q

NKT cells have special receptor that can recognize ___ complexes presenting lipids

A

CD1

75
Q

TCR have ___ and ___ chains and signal through associated ____ chains

A

alpha and beta; CD3

76
Q

what is the co-receptor for MHC found on helper T cells? What class of MHC does it bind to?

A

CD4 –> MHC2

77
Q

what is the coreceptor for MHC on cytotoxic T cells? What class of MHC does it bind to?

A

CD8; MHC1

78
Q

t/f T cell epitope are always sequential

A

t

79
Q

mitogens and superantigens bypass the ____ of B and T cells

A

antigen specificity

80
Q

superantigens are usually found in ___

A

microbes

81
Q

what antibody has high avidity?

A

IgM (5x the binding sites = 5x the avidity)

82
Q

what does it mean if there is a precipitation when an antigen is added?

A

you know the system has seen the antibody before bc it has antibodies that bind to it to form precipitates

83
Q

ELISPOT is a more intense form of ELISA that can recognize a specific secreted ___

A

cytokine

Immunology PY2 (20 decks)

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