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micr 386 > module 02 section 01 (antigens and immunogens) > Flashcards

module 02 section 01 (antigens and immunogens) Flashcards

1
Q

define “communicable diseases”

A

infectious diseases that are contagious and which can be transmitted from one source to another by infectious bacteria or viral organisms

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2
Q

approximately how many of diesase related deaths world wide are associated with communicable diseases?

A

25%

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3
Q

define “immunogenicity”

A

the ability of a susbtance to induce a humoral and/or cell mediated immune response

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4
Q

define “immunogens”

A

a molecule that has the ability to evoke a specific immune response and can react with the resultant specific antibody (e.g. humoral immunity)

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5
Q

define “antigens”

A

a molecule (soluble or processed) that can react specifically with either a preformed antibody, immunoglobulin receptors on B-cells or T-cell receptors

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6
Q

can an antigen be recognized as non-self?

A

yes, but may or may not be immunogenic

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7
Q

are immunogenicity and antigenicity the same thing?

A

no - related but have distinct immunological properties

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8
Q

how do immunogens differ from antigens?

A

an immunogen is always an antigen and always elicts an immune response, but an antigen isn’t always an immunogen - won’t always elict an immune response
(immunogen = type of antigen)

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9
Q

what are the 5 properties that contribute to the magnitude of the immune resopnse elicted by an immunogen?

A

(1) foreignness
(2) molecular size
(3) molecular complexity
(4) degradability
(5) physical form

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10
Q

describe “foreignness” in terms of the immune response elicted by an immunogen

A

the greater the phylogenetic distance (evolutionary distinctness) between two species, the greater the structural dispairty between their molecules, and thus the greater the immune response
-i.e., the bigger the difference btwn a substance and ‘self’ cells, the greater the immune response

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11
Q

define “xenogenetic”

A

different species (e.g. duck and cow)

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12
Q

define “allogenetic”

A

different individuals of the same species (e.g. chicken and duck are both birds)

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13
Q

define “syngeneic”

A

similar genetics (e.g. twins)

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14
Q

define “isogeneic/autologous”

A

same gentics (e.g. self)

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15
Q

rank allogenetic, xenogenetic, isogeneic/autologous, syngeneic in order of best immune response to worst immune response

A

xenogenetic, allogenetic, syngeneic, isogeneic/autologous

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16
Q

describe “molecular size” in terms of the immune response elicted by an immunogen

A
  • the larger the molecular size, the greater the immunogenic property
  • generally molecules with a mass greater than 10,000 Da are good immunogens
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17
Q

isulin (5700 Da), histones (6000 Da) and oxytocin (1000 Da) are ______ immunogens

A

poor

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18
Q

ovalbumin (45,000 Da), ribonuclease (14,000 Da) and immunoglobulin (160,000 Da) are _____ immunogens

A

good

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19
Q

describe “molecular complexity” in terms of the immune response elicted by an immunogen

A

internal molecular complexity is essential for good immunogens

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20
Q

are synthetic homopolymers of single amino acids or sugars immunogenic?
the addition of aromatic amino acids changes this how?

A
  • no - they’re structurally unstable

- addition of aromatics (tyr, phe, trp) enhances immunogenicity by stabilizing the structure

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21
Q

describe “degradability” in terms of the immune response elicted by an immunogen

A

antigens that are easily phagocytosed are generally more immunogenic

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22
Q

D-amino acids are _____ (good or poor) immunogens. Why?

A
  • poor
  • recall: endogenous antigens should be phagocytosed and processed first, then presented to helper T-cells by APCs
  • syntehtic polymers of d-aa cannot be processed by enzymes in phagocytosis bc naturally occuring aa are in the L-configuration
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23
Q

describe “physical form” in terms of the immune response elicted by an immunogen
(2)

A

(1) particulate antigens (aggregates of protein) are more immunogenic than soluble ones
- this is bc soluble antigens will go through body fluid and can be excreted, while particulate antigens aggregate
(2) denatured antigens are more immunogenic than when they are in their native fold
- this is bc their tertiary structure is no longer intact, resulting in different portions of the peptide exposed on the outer surface

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24
Q

what is a hapten?

A

small organic molecule that is antigenic, but not immunogenic unless it is attached to a large carrier protein

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25
Q

what do researchers use haptens for?

A

researchers use them to solicit immune responses to haptens when designing vaccines

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26
Q

describe the results when injecting a rabbit with (1) hapten, (2) carrier and (3) the hapten-carrier conjugate

A

(1) no anti-DNP antibody formation (too small to elicit an immune response)
(2) development of anti-BSA antibodies
(3) development of 3 types of antibodies:
- anti-dnp antobodies (major production)
- anti-bsa antibodies (minor production)
- anti-dnp-bsa antibodies (minor production)

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27
Q

provide a well known example of a hapten

A

penicillin

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28
Q

what happens when penicillin enters the body?

A
  • it forms a covalent bond with proteins, forming a penicilloyl-protein derivative
  • this conjugate derviative can mount an immune response in some individuals - which is why doctors ask if youre allergic to penicillin before prescribing it
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29
Q

what are adjuvants?

A

substances that enhance the immunogenicity of an antigen when injected into a human, without resulting in the mouting of an immune response against it

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30
Q

what exactly is the need for adjuvants? what does this phenomenon contribute to?

A

most antigens are soluble so they dont elict a strong immune response

  • adjuvants keep the antigen localized to tissue, preventing it from being dispersed in the body
  • this approach is the basic principle behind developing vaccines
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31
Q

what are the mechanisms by which adjuvants work? (3)

A

(1) keep the soluble immunogen localized to a tissue, acting as a depot and preventing the antigen from dispersing in the body
(2) enhancing the inflammation and developing immune response
(3) activating macrophages to digest and present the processed antigen on MHCII molecules to the helper T-cells, to develop an immune response

32
Q

how can you increase the immunogenicity of a weak immunogen? (3)

A
  • add an adjuvant
  • attach a carrier protein if the antigen is too small
  • complex it with other molecules to increase the molecular complexity
33
Q

what are epitopes?

A

the immunologically active regions of an antigen that bind to:
-antigen specific T- or B-cell receptors on lymphocytes
OR
-secreted preformed antibodies

34
Q

describe the relationship between epitopes and the production of vaccines

A
  • the production of vaccines is contingent on the epitope binding to the antigen-specific receptor (t- or b-cell receptor) to elicit the specific immune response
  • thus, an effective vaccine leads to the generation of antibodies and t-cells that are specific to a particular epitope of the infectious agent
35
Q

how do soluble antibodies bind to epitopes of exogenous antigens?

A

via weak non-covalent interactions that only operate over short distances

36
Q

what are 2 characteristics of the interactions btwn soluble antibodies and the epitopes of exogenous antigens?

A

(1) complementary shape (lock and key) of the binding site of the antibody and the epitope
(2) flat or undulating interacting surface

37
Q

can antibodies recognize epitopes consisting of amino acids that are sequential (linear) and/or non-sequential (discontinous)?

A

yes to both - but in adjacent regions due to their secondary or tertiary structure

38
Q

what are BCRs?

A

B-cell receptors: membrane bound immunoglobulin/antibodies on the b-cell surface

39
Q

what do BCRs recognize?

A

exogenous antigens

40
Q

can BCRs recognize epitopes consisting of amino acids that are sequential (linear) and/or non-sequential (discontinous)?

A

yes

41
Q

list 4 characteristics displayed by epitopes that are recognized by both secreted and membrane-bound antibodies

A

(1) multivalency
(2) immunodominance
(3) specificity
(4) accessability

42
Q

multivalency and immunodominance describe the interactions between what?

A

the epitope and the antibody

43
Q

specificity and accesability describe characteristics of what?

A

the epitopes that influence their interaction with their receptor

44
Q

describe “multivalent antigens”

A

multivalent antigens are those with multiple epitopes that can be recognized by antibodies

45
Q

what are homologous multivalent epitopes?

describe the resulting immune response.

A

these contain the same epitope repeated multiple times, resulting in a single type of immune response

46
Q

what are heterogenous multivalent antigens?

describe the resulting immune response.

A

these express different epitopes, which would result in variation in the immune response depending on the epitope recognized by the antibody

47
Q

define “immunodominant”

when does this occur?

A
  • with multivalent antigens, some epitopes will be immunodominant:
  • antigen that produces a more pronounced immune response
48
Q

what is immunodominance determined by? (3)

A
  • accessibility of the epitope
  • specificity of the binding site
  • affinity of the epitope binding to the BCR
49
Q

immunodominance is an important concept in vaccine design, true or false?
why?

A
  • true

- there will be more antibodies produced specific to the immunodominant epitope than any of the other epitopes

50
Q

accessibility of the epitope is a contributing factor to immunodominance, true or false?
why?

A
  • true

- if the antibody cannot reach the epitope, no immune response can be elicted

51
Q

antigens located between the polyalanine and polylysine backbones are _______ for antibody binding?
(available, unavailable)

A

unavailable

52
Q

what would be necessary for amino acids located at the core of a protein to be exposed to an antigen?

A

denature the protein so the specific aa sequence is exposed to the antibody

53
Q

do antibodies have a higher affinity for certain configurations of antigens over others?

A

yes

54
Q

define specificity in terms of epitope-antibody binding

A

antibodies can discriminate between antigens that differ in configuration

55
Q

how is specificity accquired?

A

by gene rearrangement

56
Q

define gene rearrangement

A

genetic recombination in developing lymphocytes

57
Q

how do acidic groups contribute to antibody specificity?

A

specificity varies depending on whether the acidic group is in the:

  • ortho: strong immune response
  • para: no response
  • meta: no response
58
Q

how do glycoside groups contribute to antibody specificity?

A

-epitopes with glycoside groups develop extreme antibody specificity due to the different alpha/beta configurations of these groups

59
Q

describe specificity using the example of galactoside and glucoside

A

the specific configuration of the OH group in galactoside requires antibody specificity to distinguish it from glucoside
(antibodies will respond to one and not the other)

60
Q

how do T-cells recgonize antigens?

A

via TCRs (t-cell receptors)

61
Q

describe what happens to proteins following phagocytosis

A

they are enzymatically degraded into smaller peptides

62
Q

what happens to the linear peptides generated via phagocytosis

A

they go through the process of binding MHC molecules

63
Q

what specific molecule is recognized by TCRs?

A

the small peptide (from phagocytosis) and the MHC molecules together

64
Q

t-cell recognition is referred to as what? describe this

A

MHC restriction

  • t-cells interact with both the MHC molecule (self) and the peptide that is bound to it (foreign)
  • it will recognize and respond to the antigen only when it is bound to the same MHC molecule
  • i.e. for T-cells, the antigens are processed and presented on MHC molecules to TCR molecules by APCs
65
Q

overview: compare the interaction btwn b-cells and t-cells with the antigen

A

b-cells: involves binary complex of membrane Ig and antigen

t-cells: involves ternary complex of T-cell receptor, antigen and MHC molecule

66
Q

overview: compare the binding of a soluble antigen for b-cells vs t-cells

A

b-cells: yes, can bind soluble protein

t-cells: no, needs to be presented on MHC molecules by APC

67
Q

overview: compare the involvment of MHC molecules for b-cells vs t-cells

A

b-cells: none required

t-cells: required to display processed antigen

68
Q

overview: comapre the epitope properties for b-cells vs t-cells

A

b-cells: accessible, hydrophillic peptides containing sequential or non-sequential aas

t-cells: internal linear peptides produced by processing of antigen and bound to MHC molecules

69
Q

what is antibody cross-reactivity?

A
  • the ability of an antibody to react with two or more antigens that possess a common epitopes
  • some responses may however be stronger than others
70
Q

epitopes of what groups contribute to antibody cross-reactivity?

A

epitopes of nonionic groups

71
Q

what are the antibdodies for blood type A?

A

anti-B

72
Q

what are the antibdodies for blood type B?

A

anti-A

73
Q

what are the antibdodies for blood type AB?

A

none - universal acceptor

74
Q

what are the antibdodies for blood type O?

A

anti-A and anti-B - universal donor

75
Q

ABO blood group antigens are ______ and have similarities to the _______

A

(1) inherited from your parents

(2) the gut microbiota

76
Q

people can develop antibodies to the gut microbiota antigens which can cross react with the ABO blood group antigens, true or false? explain.

A
  • true
  • if you are type A you will have anti-B antibodies
  • during B-cell development the b-cells specific for the A blood group antigens are clonally deleted, but if you are type AB you wont have any antibodies against type A or B antigens
77
Q

list 3 factors that may influence whether antigens are immunogenic

A

(1) the host must be genetically fit to produce an immune response to an antigen
- thus immunodeficient people are not able to mount an immune response
(2) each immunogen has an optimal concentration that is required to elicit an effective immune response
(3) route of entry of the antigen can strongly influence the organ and cell populations that are involved in the immune response, for e.g.:
- ingestion, inhalation: mucosal response
- tissue (scratch, cut): strong response in draining lymph nodes
- blood (injection): general (systemic) response, especially in the spleen.

micr 386 (31 decks)

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