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Immunology Exam 1 > Lecture 3 - Antigens > Flashcards

Lecture 3 - Antigens Flashcards

1
Q

What is the fn of the immune system?

A

to protect the body against invading organisms

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2
Q

What is an antigen?

A

any substance that can induce antibody generation (induce specific immune responses - can be bound by B or T cell receptors)
-also called immunogens

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3
Q

What do B cell receptors (Ab) recognize?

A

peptides sugars, lipids, nucleic acids and hormones

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4
Q

What do T cell receptors recognize?

A

only peptides that have been processed or degraded

-gamma/delta T cells recognize lipids directly on pathogen surface

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5
Q

what is an allergen?

A

antigen that induces an allergic reaction/immune response

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6
Q

What are epitopes?

A

smaller portions of large molecules that have the structure bound by the Ab or T cell receptor
-also called an antigenic determinant

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7
Q

Can an Ag contain more than one epitope?

A

each Ag contains many epitopes individually able to bound by Ab or T cell receptors

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8
Q

What is multivalency?

A

when epitopes are repeated several times on a macromolecule

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9
Q

How do antigenic-specific cells (B and T cells) recognize epitopes?

A

B cells have receptors (Ab) that can bind directly to the native Ag

  • T cells require presentation of the epitope by an MHC molecule
  • different lymphocytes/receptors can recognize different epitopes on the same Ag
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10
Q

What influence does spatial arrangement of epitopes on a single Ag have?

A

it affects how Abs can bind to the macromolecule

-ususally Ab epitopes are limited to those accessible to the Ab, and crowding can exclude access of Ab to all epitopes

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11
Q

How are antigenic determinants (epitopes) limited?

A

limited to those portions of the Ag that can bind to MHC molecules –> differences in the responses of different individuals

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12
Q

What if there is no MHC mol to present a particular epitope?

A

can’t generate Abs for that epitope

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13
Q

What are haptens?

A

small molecules that are not normally immunogenic but become antigens when linked to another structure (carrier) –> linkage forms a new epitope which is now big enough to be bound by Ab or T cell receptors

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14
Q

What are common results of haptens?

A

drug allergies –> common due to the tendency for them to bind larger proteins

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15
Q

Give examples of haptens?

A
  • penicillin –> binds to albumin

- urushiol –> toxic agent of poison ivy (converted to a reactive cmpd which reacts with skin proteins)

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16
Q

What are blood group Ags?

A
  • A-type blood contains an A-type enzyme
  • B-type blood contains a B-type enzyme
  • AB-type blood contain both enzymes
  • O-type blood lack both types of enzymes
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17
Q

What types of Ab do haptens generate?

A

1) against the carrier
2) against the hapten
3) against the new epitope generated by the hapten-carrier linkage
- normally don’t generate Abs against carrier (own RBCs)

18
Q

What are T independent Ag?

A

Ags that are immunogenic enough that T cells are not required to activate B cells for Ab production

  • usually very complex molecules
  • have repeating epitopes (multivalent)
  • cross-link B cell receptors (Abs) on the surface of a B cell
  • stable in vivo
19
Q

When can these T ind. Ags occur?

A

early in an immune response and assist in host clearance of certain pathogens
-B cells bind enough epitopes to Abs to activate

20
Q

What makes a good Ag (generate a strong Ab response)?

A
  • size (large)
  • Complex (last long enough so immune response can be generated)
  • intermediate stability (not too stable so T cells can’t break down)
  • Foreign enough
  • more different immunogen is from recipient –> stronger the immune response
21
Q

Rate macromolecules on how good antigens they would be (proteins, simple polysacch, complex carb,, nucleic acids, lipids)

A
  • Proteins - excellent Ags if greater than 1000Da
  • Simple Polysaccharides - poor Ags (readily degraded in cells)
  • Complex carb - usually good Ags (esp if bound to proteins)
  • Nucleic acids - usually poor Ags (unless bound to proteins)
  • Lipids - usually poor Ags (unless linked to proteins)
22
Q

What influences immunogenicity?

A

Host factors and environmental factors

23
Q

What host factors affect immunogenicity?

A

Genetics - genes that encode the specific antigen receptors can vary btw individuals
-MHC, T cell receptors, Abs
Age - specific immunity in particular is deficient in neonates and in senescent individuals

24
Q

What environmental factors affect immunogenicity?

A

dose, route of exposure, adjuvants (recognition factors)

  • increased: large, intermediate dose, complex, particular, denatured, multiple diffs, slow release, bacteria, effective interaction with host MHC
  • decreased: small, high or low dose, simple, soluble, native, few diffs, rapid release, no bacteria, ineffective interaction with host MHC
25
Q

What is cross-reactivity?

A

process by which one epitope is similar enough to trigger a response against another epitope, even on very different molecules –> specific immunity against apparently unrelated Ags

26
Q

Give an example of cross-reactivity

A

blood antigens - bacteria contain glycoproteins with carb sidechains similar to those found on RBCs

27
Q

Describe different situations of Ag exposure

A
  • Ags encountered in tissues are taken up by dendritic cells (and macrophages) tehn moved to draining lymph nodes –> elicit IgG isotype Abs
  • Ag encountered on mucosal surfaces are generally taken up through specialized M cells or via dendritic cells that extend through the epithelial lining –> elicit IgA and IgE isotype Abs
  • diff Abs elicit diff immune responses
28
Q

What is Ag processing?

A

degradation of proteins into peptides that can bind MHC molecules for presentation to T cells

29
Q

What is Ag presentation?

A

display of Ags as peptide fragments bound to MHC molecules on surface of a cell

30
Q

How are diff cell origins presented?

A
  • exogenous Ags (outside cell) –> MHC class II mols

- endogenous Ags (inside cell) –> MHC class I mols

31
Q

What are Antigen-presenting Cells?

A

highly specialized cells that can display processed Ag as peptide fragments on cell surface

32
Q

What does Ag processing involve?

A

uses surface mols encoded by Major Histocompatibility Complex

33
Q

What determines the pathway for Ag break down?

A

which class of MHC mols used which depends on origin of Ag

  • Ags in cytosol –> MHC class I (contact cytoplasm)
  • Ags from outside cell –> MHC class II (separate from cytoplasm)
34
Q

What are autoantigens?

A

self antigens
-normally ability for immune system to recognize self proteins is blocked. If errors occur, Abs and reactive T cells canb e generated against them

35
Q

Give examples of autoantigens

A

mitochondria, sperm, nucleic acids

-usually requires a host genetic predisposition for disease

36
Q

How can pathogens induce autoimmunity?

A

molecular mimicry

-infection with particular pathogens is associated with immune response against self epitopes

37
Q

What is molecular mimicry?

A

when some pathogens express proteins or carb residues that resemble host mols

38
Q

What does mol mimicry result in?

A 
activation of T cells that also recognize host cell proteins presented by normal, homeostatic MHC class I mols
-sequestered self Ags may be released following damage by pathogens --> exposes them to adaptive immune cells
39
Q

Name some types of Ag associated with pathogens or infections

A

H antigens - flagellum
F antigens - pili
K antigens - capsule
O antigens - cell wall

40
Q

What are tumor antigens

A

self antigens used to identify tumors (not expressed often)

  • presented on surface of tumor cells by MHC class I and II mols
  • not found on normal cells
41
Q

What are superantigens?

A
  • usually secreted exotoxins that are highly mitogenic and stimulatory for T cells
  • don’t require prior processing in order to bind to T cell receptor
  • most work by cross-linking MHC and TCR to overstimulate T cells and drive hyperinflammation
  • T cell thinks there’s an epitope and creates an immune response
42
Q

What’s the difference btw innate and adaptive?

A

innate system recognizes many chemical structures or signatures without first processing a larger mol

  • determinants recognized by innate immmune system differ from those recognized by adaptive immune system
  • Abs, B/T cell receptors recognize discrete determinants and demonstrate high degree of specificity
  • innate immune system recognize broad molecular patterns found in pathogens but NOT in host –> lack a high degree of specificity –> sometimes called Pathogen Associated Molecular Patterns (NOT antigens)

Immunology Exam 1 (7 decks)

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