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CRG RUSVM Immunology > antigens > Flashcards

antigens Flashcards

1
Q

how was the word antigen come about

A

it was a combination of the words antibody and generator

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2
Q

what are antigens

A
  • antigens are molecules or pieces of molecules that bind to antibodies, MHC molecules or TCRs
  • Molecules that induce an immune response when introduced into the body
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3
Q

what are the two sub categories of antigens

A
  • immunogens
  • haptens
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4
Q

what are immunogens

A

immunogens are a substance capable of stimulating an immune response

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5
Q

what are haptens

A

haptens are substances that will not by themselves stimulate an immune response but can do so when complexed with a larger molecules, such as a host protein

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6
Q

what are the two cardinal features of antigens

A
  • Immunogenicity
  • antigenicity
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7
Q

what is immunogenicity

A

antigens are capable of inducing an immune response (t cells, B cells - Ab)

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8
Q

What is antigenicity

A

antigenicity is when antigens are capable of binding with products of the immune response that they induced (i.e., Lymphocytes or antibodies)

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9
Q

What are the functions of Epitope or antigenic determinant

A

Epitope or antigenic determinant is a part of an antigen that is actually responsible for inducing the immune response and binding to the products of the immune response (lymphocyte receptors and antibodies)

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10
Q

what are the sources of antigens

A
  • Infectious agents such as (microbial antigens)
    • bacteria
    • viruses
    • parasites
    • Fungi
  • Altered self-antigens
    • Tumors
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11
Q

what are the factors that affect the immunogenicity of antigens

A
  • Foreignness
  • size
  • chemical composition
  • Physical properties
  • Degradability
  • genetic factors
  • age
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12
Q

How does Foreignness affect the immunogenicity of antigens

A

The immune system distinguishes between self and non-self and only self substances are immunogenic and induce immune response (with exceptions)

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13
Q

How does size affect the immunogenicity of antigens

A

there is no absolute size at which antigens become more immunogenic, however, the larger the antigen the more immunogenic is can be

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14
Q

How does chemical composition affect the immunogenicity of antigens

A

complex molecules are usually immunogenic (chance of diverse antigenic determinants)

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15
Q

what are the two physical properties that affect immunogenicity of antigens

A
  • Particulate antigens
    • are more immunogenic than soluble antigens
  • Denatured antigens
    • are more immunogenic than native forms (denaturation exposes more antigenic determinants)
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16
Q

How does Degradability affect the immunogenicity of antigens

A

antigens that are phagocytosed and easily degraded are usually highly immunogenic

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17
Q

How does Genetic factors affect the immunogenicity of antigens

A
  • some antigens are more immunogenic for a given species than for the other. Similarly, some antigens are more immunogenic for an individual than the other
    • species or individuals may have genetic variations in genes encoding antigen receptors or both T or B cells
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18
Q

How does age affect the immunogenicity of antigens

A

young or old individuals usually have less capability to mount an immune response compared to the middle-aged in relation to the same antigen

19
Q

what are the chemical nature of antigens we are concerned with

A
  • Proteins
    • by far the largest group of antigens
  • polysaccharides
  • Nucleic acids
  • Lipids
20
Q

how do the proteins affect the chemical nature of antigens

A

most proteins are highly immunogenic (pure proteins, glycoproteins or lipoproteins)

21
Q

how do the polysaccharides affect the chemical nature of antigens

A

pure polysaccharides and lipopolysaccharides are usually good immunogens (pneumococcal polysaccharides may require conjunction)

22
Q

how do the nucleic acids affect the chemical nature of antigens

A

weak antigens may become highly immunogenic when conjugated to proteins

23
Q

how do the Lipids affect the chemical nature of antigens

A

generally not immunogenic but some may be heptanes

24
Q

what are adjuvants

A

a substance that enhances the body’s immune response to an antigen

25
Q

what are exogenous antigens

A

antigens that have entered the body from outside (i.e. inhalation, ingestion, or infection

26
Q

what are endogenous antigens

A

antigens that are generated within cells as a result of normal cell metabolism or because of viral or intracellular bacterial infection

27
Q

what are the 5 types of antigens

A
  1. T-independent antigens
  2. T-dependent antigens
  3. superantigens
  4. Haptens
  5. Autoantigens
28
Q

what are T independent antigens

A

antigens that directly stimulate B lymphocytes do produce antibodies without the need of helper T cells, (ie, lipopolysaccharides are T independent antigens)

29
Q

what are the properties of T-independent antigens

A
  1. have a polymeric structure
    1. the same antigenic determinants repeats several times throughout the length of the antigen
  2. May activate lymphocytes polyclonally
    1. I.e. B cells of different antigenic specificity may be activated
  3. Resistant to degradation
    1. do not easily degrade, therefore, may last longer and stimulate B lymphocytes much longer
30
Q

what are T- dependent antigens

A

antigens that indirectly stimulate B lymphocytes to produce antibodies

31
Q

what are the characteristics of T-dependent antigens

A
  • The presence of helper T cells is required for stimulation, hence the name T-dependent
  • Protein are mostly T-dependent antigens
  • structurally, they contain a few copies each of various antigenic determinants throughout the length of the antigen
32
Q

what is the purpose of superantigens

A

superantigens can activate a large number of lymphocytes at one time (non-specifically)

33
Q

where are superantigens mostly derived from

A

superantigens are mostly derived from bacteria or viruses

34
Q

where do superantigens bind to t cells

A

they bind to the variable domain of the Beta(Vbeta) chain in the T cell receptor (TCR) of CD4+ T cells and the alpha chain of the MHC class 2 molecule on antigen-presenting cells

35
Q

what is the result of superantigens to the TCR and MHC class 2 molecules

A

induces a very strong signal that activates a large number of T cells, polyclonally

36
Q

Polyclonal activation of helper T lymphocytes leads to

A

excessive production of IL-1, IL-2, IL-6, TNFalpha, MIP-1alpha, and MIP-1beta which may lead to systemic toxicity

37
Q

what are haptens

A

small non-immunogenic substances (I.E. metabolites of antibiotics such as penicilloyl from penicillin)

38
Q

Can Haptens induce an immune response

A

Haptens on their own cannot induce an immune response

39
Q

how can haptens induce an immune response

A

only if they become conjugated to a carrier (I.E. protein)

40
Q

why are haptens incomplete antigens

A

because they lack immunogenicity

41
Q

what are autoantigens

A

autoantigens are natural constituents of the body, as opposed to foreign antigens

42
Q

what is the function of Autoantigens

A

they play a role autoimmunity- reactions of the immune system against host antigens

43
Q
A

CRG RUSVM Immunology (8 decks)

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