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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
Q

the affinity of an Ab for an Ag is related to

A

the ratio of the rates of the forward reactions for formation of the complex to back reaction for the decay of the complex

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26
Q

the reaction between Ab and Ag moves backwards and forwards depending on

A

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

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27
Q

Each Y antibody contains

A

4 polypeptides

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28
Q

the 4 polypeptides are made up of

A

2 identical heavy chains (55kDa each)

2 identical light chains (22kDa each)

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29
Q

weight of heavy chain

A

55kDa

30
Q

weight of light chain

A

22kDa

31
Q

how are the 4 polypeptide chains held together

A

through disulphide bridges and non-covalent bonds

32
Q

somatic mutation

A

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
Q

isotope switching

A

is a biological mechanism that changes a B cells production of immunoglobulin from one type to another

34
Q

example of isotope switching

A

isotope IgM to isotope IgG

–> IgG becomes a better fit as it mutates

35
Q

Fab domain

A

2 domains which carry the antigen binding site

- fragments having the antigen binding site

36
Q

Fc domain

A

third domain

- the fragment that crystallizes

37
Q

the hinge in the antibody allows

A

contortion

-bringing the fab domain closer to allow recognition of PAPM (epitope)- not rigid

38
Q

the ability to bind antigens is determined by the

A

N terminal domain

- these differ considerably between antibodies of differing specificities are termed ‘variable’ or ‘v’ domains

39
Q

Describe the Fab domain

A

made up of x 2 VL/VH/CL/CH

40
Q

light chain on the

A

bottom

41
Q

Fc domain allows

A

binding to cell after epitope binding and also complement binding

42
Q

variable light (VL) and variable heavy (VH) chains

A

sequence analysis of amino acids VH and VL regions reveal small regions fo hypervariability within 4 conserved framework rgeions

43
Q

which 4 conserved framework regions show hypervariability

A

Fr1,Fr2, Fr3, Fr4

44
Q

how do these hypervariability cause variable binding sites

A

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
Q

what give specific affinity and binding capability to target antigen

A

CDRs

46
Q

5 main classes of immunoglobulins

A

IgG(gamma) IgM IgA(alpha) IgE and IgD (delta)

47
Q

how are these 5 classes divided

A

on the basis of the number of Y-like units and the type of heavy chain polypeptide they contain e.g. gamma, alpha

48
Q

heavy chain is always denoted by

A

the class of polypeptide chain - e.g. gamma, alpha, delta etc

49
Q

5 different types of

A

heavy chain

50
Q

how many types of light chain

A

2

51
Q

types of light chain

A

kappa, lambda

52
Q

one light chain always

A

associates wityh one heavy chain, so the number of light chains is always equal to the number of heavy chains

53
Q

how many subclasses of IgG in humans

A 
4
IgG1- gamma1 (heavy chain)
IgG2-gamma2
IgG3-gamma3
IgG4-gamma4
54
Q

IgA has how many sub-classes

A

IgA1 and IgA2

- these have alpha1 and alpha2 chains respectively

55
Q

what did Rodney Porter

A

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
Q

today Porters fraction I and II are termed

A

Fab

57
Q

III fraction

A

Fc

- this fraction could be crystalised

58
Q

porter initially thought

A

antibodies consisted of a single polypeptide chain

59
Q

Edelman showed that

A

IgG consisted of 4 chains, a pair of heavy and light chains to give a Y config

60
Q

both Porter and Edelman worked with

A

IgG

61
Q

papains were used to show that

A

antibodies are made up of 4 polypeptides

  • causes fragmentation
  • pepsin cm also be used
62
Q

papains breaks an antibody into how many parts

A

3: x2 fab and 1 Fc

63
Q

antibodies must be able to cross mucosal barriers in order to

A

reach the pathogen

64
Q

what do antibodies use to cross

A

secretory components

65
Q

secretory components

A
  • helps IgA moveout of the bloodstram and sit on mucosal linings
66
Q

J chains

A

a loop which holds` chains together e.g. IgM and IgA

67
Q

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)

A

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
Q

which is the most prevalent antibody on mucosal linings

A

IgA

69
Q

epithelial cells in the intestine

A

mediate the transfer of dimeric serum IgA to the intestinal lumen via polymeric Ig receptor

70
Q

the polymeric Ig receptor binds to

A

the secretory component, moving the antibody into the gut

- binds to antigen and prevents uptake of bacteria and toxins

71
Q

trans epithelial transport of IgA

A
  • 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
Q

once in the lume IgA is able to

A

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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