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Immunology > 3. Antigens and Antigen Receptors > Flashcards

3. Antigens and Antigen Receptors Flashcards

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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
antibody pentamer
M
26
B cell antigen receptor (BCR) complex
Comprises membrane-bound Ig (mIg) AND 2 Igα and 2 Igβ chains (CD79a and CD79b)
27
ITAMs
Immunoreceptor Tyrosine kinase | Activatory Motif - important for signal transduction, in cytoplasmic chains
28
ITAM signalling leads to...
development of either plasma or | memory cells
29
where are Immunoglobulin-antigen interactions located?
at the furthest extreme of the heavy (VH) and light chains (VL)
30
why is a high affinity antibody is more protective than a low affinity antibody
it will bind antigens at lower concentrations
31
avidity
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
immunoglobulin fold
a protein domain of Anti-parallel β-pleated strands and includes a disulfide bridge
33
what are the Two types of TCR
αβ and γδ
34
how many antigen binding sites do TCRs have?
one
35
how does TCR signal?
it can't itself - instead CD3 does
36
CD3 structure
consists of 6 polypeptides; ζζ, γε and εδ dimers
37
MHC class I recognised by...
CD8 - cytotoxic
38
MHC class II recognised by...
CD4 - helper
39
classical T cell activation steps
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
superantigens
proteins that bypass normal antigen recognition. not processed by antigen presenting cells
41
where do superantigens bind to in order to bypass normal antigen recognition?
– non-variable sequences of TCR variable regions | – non-polymorphic sequences of MHCII α-chain
42
where are γδ T cells found?
mostly in epithelial rich | tissues e.g. foetus, mucosa
43
how do γδ T cells differ from αβ T cells?
``` less diverse. recognise antigen presented in CD1 rather than MHC. recognise lipids, pathogens (such as M. tuberculosis) and pathogenic toxins ```
44
presentation
how complex antigens/proteins are broken down | into peptides and loaded into molecules
45
MHC class 1 recognises...
endogenous antigens
46
MHC 2 recognises...
exogenous antigens
47
MHC 1 structure
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
where is MHC 1 found?
on all nucleated cells & platelets
49
where is MHC 2 found?
On professional Antigen presenting cells - Dendritic cells Macrophages B cells
50
MHC 2 structure
two chains a and b
51
dendritic cells location
Skin GI and respiratory tracts Parenchyma
52
capture and presentation of protein antigens by dendritic cells
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
processing endogenous antigens
processed by proteasome and imported into ER. loaded into MHC 1 and transported to cell membrane
54
processing exogenous antigens
engulfed into endocytic vesicles and degraded. loaded into MHC 2 and transported to cell membrane
55
how are proteins marked for degradation?
ubiquitination
56
TAP
transporter associated with antigen processing
57
immunoglobulin genes contain...
– V = Variable Segments – D = Diversity Segments – J = Joining Segments
58
positive selection of b cell development
cells that cannot make functional heavy or light chains die by apoptosis
59
negative selection of b cell development
cells that bind to self | molecules whilst arranging their BCRs die by apoptosis
60
when does thymocyte expression of TCR begin?
after rearrangement | of the DVJ segments genes encoding α and β chains
61
HLA
Human leukocyte antigens - a single stretch found on Chromosome 6 in humans that contains genes for the MHC and other immune-related genes
62
MHC 1 HLA genes
A, B and C
63
MHC 2 HLA genes
DP, DQ and DR
64
advantage of diverse MHCs
provides resilience in a population to emerging pathogens
65
disadvantage of diverse MHCs
makes tissue typing in organ transplantation essential to avoid rejection of the organ as “non-self”
66
polyclonal response
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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