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Cellular basis of immunity > Antibodies > Flashcards

Antibodies Flashcards

1
Q

what are they

A

host proteins produced in response to pathogens or in response to PAMPs

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2
Q

what produce them

A

plasma cells

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3
Q

plasma cells

A

b cell effector- lymphoid lineage

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4
Q

part of the

A

adaptive system

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5
Q

are they soluble?

A

yes

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6
Q

how do they clear infection- simple

A

find antigen to bind to, then antigen-antibody complexes are removed from circulation through phagocytosis by macrophages (primarily)

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7
Q

Linus Pauling

A

became interested in how the polypeptide structure of an antibody moults itself around the antigen

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8
Q

what did Pauling suggest

A

that pre-formed undifferentiated ‘immunoprotein’ folded over the antigenat different locations are different haptenic groups.
- proposed that a single immunoprotein reacted with all antigens but its conformation was different in each case

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9
Q

who realised Pauling was wrong?

A

Sir Frank MacFarlane Burnet

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10
Q

what did Burnet propose

A

‘clonal selection theory’ of acquired immunity
- realised that during the immune response certain cells were selected for antibody production

-proposed that somatic mutation during embryonic life generates the random specificities of antibodies that cells possess concordant antigen receptors and that cells to self-antigens are killed

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11
Q

clonal selection-simple

A

start with large pool of antbiodies, all tested, then left with B cell capable of recognizing antigen but wont harm self tissue

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12
Q

what happens to b cells when infection goes

A

B cell populaton decreases and become memory b cells

- sit in lymphatic tissue waiting to be challenged again

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13
Q

induction of B cell antibody response by T cell

A

1) dendritic cells displaying antigen arrives at lymph nodes
2) activate CD4 specific T cells which proliferate and mature into effector cells
3) these T cells are capable of activating antigen specific B cells
4) once activated by CD4 specific T cells, the B cell proliferates to form a primary focus of antigen specific B cells
5) B cells from primary focus migrate to nearby follicles and proliferate
6) other B cells start secreting some antibodies, but eventually die (not specific to T cell)
7) specific B cells in follicle begin to proliferate rapidly- somatic mutation occurs to introduce variation into B cell receptor
8) B cells undergo selection after somatic mutation- clonal mutation
9) those which fail to bind die

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14
Q

strucutre

A
  • large family of glycoproteins

- share key functional and structural features

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15
Q

shared functional features

A

able to bind both to and antigens and specialised cells and proteins of the immune system

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16
Q

shared structural features

A

COMPOSED OF ONE OR MORE COPPIES OF CHARACTERISITC UNIT THAT FORMS A Y SHAPE

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17
Q

antibodies bind to a specific

A

amino acid

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18
Q

any molecule or parts of molecules recognised by the variable antigen receptor of lymphocytes are

A

antigens

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19
Q

antibodies do not

A

recognise the whole protein, just the amino acid

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20
Q

if the amino acid is changed

A

antibody will no longer be able to recognise

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21
Q

the epitope

A

specific region of the antigen bound by the variable region of an immunoglobulin

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22
Q

paratope

A

is the antigen-binding region of an antibody

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23
Q

affinity

A

is the measure of the strength of binding of an antigen by antibody

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24
Q

antibody binding is

A

non-covalent and reversibly

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25
the affinity of an Ab for an Ag is related to
the ratio of the rates of the forward reactions for formation of the complex to back reaction for the decay of the complex
26
the reaction between Ab and Ag moves backwards and forwards depending on
whether another antibody comes along with a better fit - so if an antibody comes along and has a reasonable fit it will bind, but as the B cells go through somatic mutation to make better fitted antibodies the first antibody will lift off and allow the antibody with the better fit to bind
27
Each Y antibody contains
4 polypeptides
28
the 4 polypeptides are made up of
2 identical heavy chains (55kDa each) | 2 identical light chains (22kDa each)
29
weight of heavy chain
55kDa
30
weight of light chain
22kDa
31
how are the 4 polypeptide chains held together
through disulphide bridges and non-covalent bonds
32
somatic mutation
when genes rearrange so the antibodies get a better and better fit, therefore certain clonal lineages which have the best clonal fit to the antigen
33
isotope switching
is a biological mechanism that changes a B cells production of immunoglobulin from one type to another
34
example of isotope switching
isotope IgM to isotope IgG | --> IgG becomes a better fit as it mutates
35
Fab domain
2 domains which carry the antigen binding site | - fragments having the antigen binding site
36
Fc domain
third domain | - the fragment that crystallizes
37
the hinge in the antibody allows
contortion | -bringing the fab domain closer to allow recognition of PAPM (epitope)- not rigid
38
the ability to bind antigens is determined by the
N terminal domain | - these differ considerably between antibodies of differing specificities are termed 'variable' or 'v' domains
39
Describe the Fab domain
made up of x 2 VL/VH/CL/CH
40
light chain on the
bottom
41
Fc domain allows
binding to cell after epitope binding and also complement binding
42
variable light (VL) and variable heavy (VH) chains
sequence analysis of amino acids VH and VL regions reveal small regions fo hypervariability within 4 conserved framework rgeions
43
which 4 conserved framework regions show hypervariability
Fr1,Fr2, Fr3, Fr4
44
how do these hypervariability cause variable binding sites
the hype variable regions form loops that combine together to form the principle antigen binding surfaces- determine variability within antibody structure - these surfaces re called complementarity determining regions CDRs (CDR1 etc)
45
what give specific affinity and binding capability to target antigen
CDRs
46
5 main classes of immunoglobulins
IgG(gamma) IgM IgA(alpha) IgE and IgD (delta)
47
how are these 5 classes divided
on the basis of the number of Y-like units and the type of heavy chain polypeptide they contain e.g. gamma, alpha
48
heavy chain is always denoted by
the class of polypeptide chain - e.g. gamma, alpha, delta etc
49
5 different types of
heavy chain
50
how many types of light chain
2
51
types of light chain
kappa, lambda
52
one light chain always
associates wityh one heavy chain, so the number of light chains is always equal to the number of heavy chains
53
how many subclasses of IgG in humans
``` 4 IgG1- gamma1 (heavy chain) IgG2-gamma2 IgG3-gamma3 IgG4-gamma4 ```
54
IgA has how many sub-classes
IgA1 and IgA2 | - these have alpha1 and alpha2 chains respectively
55
what did Rodney Porter
using the enzyme papain, Porter showed that gamma-globulin consisted of three factions I, II, III - showed that I and II bound antigen without forming a precipitate - notes the possibility that fractions 1 and II could lie either side of fraction III
56
today Porters fraction I and II are termed
Fab
57
III fraction
Fc | - this fraction could be crystalised
58
porter initially thought
antibodies consisted of a single polypeptide chain
59
Edelman showed that
IgG consisted of 4 chains, a pair of heavy and light chains to give a Y config
60
both Porter and Edelman worked with
IgG
61
papains were used to show that
antibodies are made up of 4 polypeptides - causes fragmentation - pepsin cm also be used
62
papains breaks an antibody into how many parts
3: x2 fab and 1 Fc
63
antibodies must be able to cross mucosal barriers in order to
reach the pathogen
64
what do antibodies use to cross
secretory components
65
secretory components
- helps IgA moveout of the bloodstram and sit on mucosal linings
66
J chains
a loop which holds` chains together e.g. IgM and IgA
67
within your gut there are m cells (sampling cells- which take info from the gut and relay to dendiritc cells- which feed info to the rest of the immune system)
antibody being released by B cell needs to move from the blood into the lumen where is can have an effect on the pathogen/toxin B CELL CANNOT DO THIS- ONLY ANTIGEN
68
which is the most prevalent antibody on mucosal linings
IgA
69
epithelial cells in the intestine
mediate the transfer of dimeric serum IgA to the intestinal lumen via polymeric Ig receptor
70
the polymeric Ig receptor binds to
the secretory component, moving the antibody into the gut | - binds to antigen and prevents uptake of bacteria and toxins
71
trans epithelial transport of IgA
- IgA dimer with j chain attached binds to the polymeric Ig receptor- a transmembrane protein expressed at the basal surface of epithelial cells of the gut, airways and various secretory glands-binding of IgA induces transcytosis of the polymeric Ig receptor - complex is delivered to the apical surface of the epithelial cell and into the lumen - proteases cleave the plgR near the membrane releasing the majority of the extracellular domain still bound to IgA dimer - the secretory component protects IgA from proteases present in the mucus and anchors IgA at the dimer - the secretory component protects IgA from proteases present in mucus and anchors IgA a the desired location
72
once in the lume IgA is able to
complex with toxins and bacteria, signalling for phagocytotic cells to bind to the Fc domain of the antibody and destroy the complex

Cellular basis of immunity (59 decks)

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