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Immunology > 3. Antigens and Antigen Receptors > Flashcards

3. Antigens and Antigen Receptors Flashcards

1
Q

Paratopes

A

antigen binding sites on antigen receptors

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2
Q

Epitopes/antigenic determinant

A

the part of the antigen that binds to paratopes

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3
Q

immunogen

A

any molecule or group of molecules

that induce an immune response

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4
Q

hapten

A

Small molecule that can act as an

epitope but not elicit an immune response

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5
Q

Non microbe derived antigens

A

pollen, food and dust or ‘self’ antigens

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6
Q

how do antigens enter the body?

A

– breaks in the skin and mucous membranes,
– direct injection, as with a bite or needle or through
– organ transplants and skin grafts
– M cells in the mucosal surfaces

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7
Q

complex antigens

A

have many different antigenic determinants - e.g. viruses

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8
Q

Adjuvants

A

enhance the immune response to an antigen,

making it more immunogenic

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9
Q

what do adjuvants increase?

A

• persistence (‘depot’)
• effective size (for uptake by APCs)
• activation of dendritic cells, macrophages →
inflammatory cytokine production

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10
Q

examples of adjuvants

A

• Complete Freund’s adjuvant (oil, water, dead/lysed
mycobacteria)
• Alum (aluminium potassium sulphate)

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11
Q

what do T cells bind to?

A

linear arrays of

approximately 9 amino acids - antigens that have been broken down into peptides and presented on cells

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12
Q

immunoglobulins

A

proteins that recognize and bind to a particular antigen with very high specificity

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13
Q

how do BCR and B cell antibodies differ structurally?

A

BCR has a short cytosolic tail

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14
Q

Fab region

A

contains the variable

antigen binding site

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15
Q

Fc region

A

rest of the molecule has a relatively constant structure

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16
Q

how many variable regions are there in the antigen binding site?

A

2 - heavy and light

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17
Q

what type of chains are light constant regions?

A

kappa or lamda

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18
Q

what type of chains are heavy constant regions?

A

mu, gamma, alpha, delta and epsilon

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19
Q

CDRs

A

complementarity-determining regions - immunoglobulin-like domains that
contain 3 hypervariable loops between
the strands of the β-pleated sheets

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20
Q

IgM

A

Found on the surface of naïve B cells

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21
Q

IgA, IgE and IgG

A

Found on the surface of B cells that have been

activated and have undergone “class-switching”

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22
Q

IgD

A

Found on all B cells

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23
Q

antibody monomers

A

G, D and E

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24
Q

antibody dimer

A

A

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25
Q

antibody pentamer

A

M

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26
Q

B cell antigen receptor (BCR) complex

A

Comprises membrane-bound Ig (mIg)
AND 2 Igα and 2 Igβ chains (CD79a
and CD79b)

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27
Q

ITAMs

A

Immunoreceptor Tyrosine kinase

Activatory Motif - important for signal transduction, in cytoplasmic chains

28
Q

ITAM signalling leads to…

A

development of either plasma or

memory cells

29
Q

where are Immunoglobulin-antigen interactions located?

A

at the furthest extreme
of the heavy (VH) and light chains
(VL)

30
Q

why is a high affinity
antibody is more protective than a low
affinity antibody

A

it will bind
antigens at lower
concentrations

31
Q

avidity

A

the total strength of binding of the Fab
regions of the population of antibodies raised against an antigen, and
involves the reaction with all antigenic determinants

32
Q

immunoglobulin fold

A

a protein domain of Anti-parallel β-pleated strands and includes a disulfide bridge

33
Q

what are the Two types of TCR

A

αβ and γδ

34
Q

how many antigen binding sites do TCRs have?

A

one

35
Q

how does TCR signal?

A

it can’t itself - instead CD3 does

36
Q

CD3 structure

A

consists of 6 polypeptides; ζζ, γε and εδ dimers

37
Q

MHC class I recognised by…

A

CD8 - cytotoxic

38
Q

MHC class II recognised by…

A

CD4 - helper

39
Q

classical T cell activation steps

A
  1. variable regions of TCR interact with peptide in MHC
  2. epitope must be complementary to paratope
  3. CD4/8 joins the complex
  4. kinases and ITAMs stimulate activation
40
Q

superantigens

A

proteins that bypass normal antigen recognition. not processed by antigen presenting cells

41
Q

where do superantigens bind to in order to bypass normal antigen recognition?

A

– non-variable sequences of TCR variable regions

– non-polymorphic sequences of MHCII α-chain

42
Q

where are γδ T cells found?

A

mostly in epithelial rich

tissues e.g. foetus, mucosa

43
Q

how do γδ T cells differ from αβ T cells?

A 
less diverse.  recognise 
antigen presented in 
CD1 rather than MHC.  recognise lipids, pathogens (such 
as M. tuberculosis) and 
pathogenic toxins
44
Q

presentation

A

how complex antigens/proteins are broken down

into peptides and loaded into molecules

45
Q

MHC class 1 recognises…

A

endogenous antigens

46
Q

MHC 2 recognises…

A

exogenous antigens

47
Q

MHC 1 structure

A

single polypeptide chain, bound to β2-microglobulin. a1 and a2 domains consist of 4 b strands and an a helix. These form a groove or cleft which is the Ag-binding site

48
Q

where is MHC 1 found?

A

on all nucleated cells & platelets

49
Q

where is MHC 2 found?

A

On professional Antigen presenting cells - Dendritic cells Macrophages B cells

50
Q

MHC 2 structure

A

two chains a and b

51
Q

dendritic cells location

A

Skin
GI and respiratory tracts
Parenchyma

52
Q

capture and presentation of protein antigens by dendritic cells

A
  1. antigen is processed
  2. dendritic cells become migratory - detach and enter lymphatics
  3. enter paracortex area of lymph nodes
  4. then become positioned on the fibroblastic reticular cell network
  5. scanned by naive CD4/8 T cells
53
Q

processing endogenous antigens

A

processed by proteasome and imported into ER. loaded into MHC 1 and transported to cell membrane

54
Q

processing exogenous antigens

A

engulfed into endocytic vesicles and degraded. loaded into MHC 2 and transported to cell membrane

55
Q

how are proteins marked for degradation?

A

ubiquitination

56
Q

TAP

A

transporter associated with antigen processing

57
Q

immunoglobulin genes contain…

A

– V = Variable Segments
– D = Diversity Segments
– J = Joining Segments

58
Q

positive selection of b cell development

A

cells that cannot make functional heavy or light chains die by apoptosis

59
Q

negative selection of b cell development

A

cells that bind to self

molecules whilst arranging their BCRs die by apoptosis

60
Q

when does thymocyte expression of TCR begin?

A

after rearrangement

of the DVJ segments genes encoding α and β chains

61
Q

HLA

A

Human leukocyte antigens - a single stretch found on
Chromosome 6 in humans that contains genes for the MHC and other immune-related
genes

62
Q

MHC 1 HLA genes

A

A, B and C

63
Q

MHC 2 HLA genes

A

DP, DQ and DR

64
Q

advantage of diverse MHCs

A

provides resilience in a population to emerging pathogens

65
Q

disadvantage of diverse MHCs

A

makes tissue typing in organ transplantation essential to avoid rejection
of the organ as “non-self”

66
Q

polyclonal response

A

many
clones of B and T cells will expand as they recognise
the different antigens and/or different epitopes within
them

Immunology (9 decks)

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