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Biomolecular Mechanisms > Week 17: (C) Immunoglobulins > Flashcards

Week 17: (C) Immunoglobulins Flashcards

1
Q

Where is IgA found?

major antibody where?

A

seromucous secretions

e.g. saliva, milk, colostrum, gut, tracheobronchial system & genito-urinary system

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2
Q

When is IgA encountered?

A

first encountered by many invading pathogens.

2most prevalent antibody in serum after IgG

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3
Q

What is the most abundant antibody?

A

IgA

found in serums

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4
Q

What are the 2 sub-classes of IgA?

A

1 and 2

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5
Q

What 2 forms can IgA have?

A

monomeric and dimeric forms

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6
Q

What structure is IgA in serum?

A

monomeric

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7
Q

How much is IgA1 and IgA2 in monomeric form?

A

90% IgA1

10% IgA2

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8
Q

What structure is IgA in secretions?

A

mostly dimeric

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9
Q

What percents of IgA1 and IgA2 are in secretions?

A

40% IgA1

60% IgA2

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10
Q

What additional component is in the secretory IgA?

A 
additional polypeptide (secretory component).
derived from receptor mediating sport to the secretions. 
Carries IgA into the secretions
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11
Q

What is the secretory component?

A

Additional polypeptide in the secretory IgA.

Carries IgA into secretions

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12
Q

What does the secretory component protect IgA from?

A

harsh environment

extremes of pH and proteolytic enzymes present.

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13
Q

Are IgA’s N-linked?

A

GLYCOSYLATED, decorated with N-liked oligosaccharides.

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14
Q

What additional oligosaccharides does IgA1 have?

A

O-linked sugars, attached thing region

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15
Q

What are O-linked oligosaccharides attached to?

A

Ser or Thr residues

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16
Q

Where is secretory IgA produced?

A

locally at the mucosal surfaces

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17
Q

What structure is secretory IgA?

A

dimeric

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18
Q

What holds the SIgA together?

A
  • J-chain (middle the tails)

- Secretory component CH2 through the J-chain to the other CH2 of other chain

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19
Q

how many globular domains does the secretory component have?

A

5

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20
Q

Where is the secretory component derived from?

A

receptor that carried the dimeric IgA out into the secretions

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21
Q

IgA has 4 ABS, what is this called?

A

polyvalent

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22
Q

What can IgA be described as?

A

antiseptic paint. Agglutinates pathogens.

Pathogens prevented from crossing the epithelium and rushed from body

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23
Q

How many heavy chain globular domains does IgE have?

A

5

24
Q

How many heavy chain globular domains does IgA have?

A

4

25
Q

Does IgE have a lotto oligosaccharides attached?

A

YES

26
Q

What response is ice associated with?

A

allergic response

protection in parasitic infections

27
Q

What immunoglobulin done know the least about?

A

IgD

28
Q

What concentration is IgD in serum

A

Low conc

29
Q

Where is IgD found?

A

surface lymphocytes

30
Q

What is the function of IgD?

A

unclear, may be involved control of antibody response

OR// mucosal immune system

31
Q

How do antibodies block virus from binding to and invading host cell?

A

1) block binding receptors on virus–> block fusion event

2) agglutination–>multiple ab and viruses clumped together

32
Q

How do antibodies block entry of pathogens into host cells?(bacterial)

A

antibodies block colonisation

Also agglutinate

33
Q

What do bacterial pathogens bind to?

A

colonise on cell surface via bacterial adhesions

34
Q

What is the action of town poisoning a cell?

A

1) toxin binds to receptor
2) endocytosis of toxin- receptor complexes
3) Dissociation of toxin to release the active chain, poisoning cell

35
Q

How do antibodies block the binding of toxin?

A

bind to toxin and block

Neutralisation

36
Q

What antibodies are efficient in binding soluble toxins?

A

IgG & IgA

37
Q

What are antibodies called that prevent a toxin binding to cell surface receptors?

A

neutralising antibodies

38
Q

It’s not only the recognition site on the Fab region that is associated with protective function, but what does the Fc region do?

A

effector function

interact with effector molecules

39
Q

What 3 pathways can result in complement activation?

A

classical, lectin & alternative

40
Q

What complement pathways can be activated directly via pathogen?

A

lectin & alternative

41
Q

What compliment pathway does IgM and IgG need to recognise pathway before activation?

A

Classical

42
Q

What activation any of the 3 compliment pathways lead to?

A

C3 convertase enzymatic activity.

cleavage of C3 —>c3b+C3a

43
Q

What can C3b initiate?

A

1) feedback to alternative pathway
2) opsonisation
3) C5–>C5b+C5a …
C6-C9 … membrane stack process (punch hole into membrane) = LYSIS

44
Q

What conformational change does IgM undergo when binding to antigenic surface?

A

planar to staple confo

45
Q

When IgM is in stable confo, what can recognise and bind to it?

A

C1q

46
Q

How many IgG molecules are bound to antigenic surface?

A

6

47
Q

What conformation does the IgG make when bound to antigen cell surface?

A

cluster together
Fab arms facing the outside
Fc create a platform in the middle

48
Q

What does the C1q recognise in the IgG?

A

the Fc platform

49
Q

What stops inappropriate activations of the C1q complement to IgG?

A

need a cluster of 6, individual IgGs cannot activate

50
Q

What does activation of C1q activate?

A

C1r –> cleaves and activates C1s.

further steps trigger lysis of target cell

51
Q

What are the 2 types of effector molecules can interact with the Fc region?

A

C1q & fc receptors (specific to different types Igs)

52
Q

How can Fc receptor- mediated pathways cause clearance of pathogen?

A

1) free Ig bind to Fc receptors but don’t cross-link (no neighbouring Fc R activated). macrophage not activated.

2) Specific IgG recognise antigenic determinants on a bacterial cell, closely associated together.
Engagement of neighbouring Fc receptors = cross-linked on surface of the cell —> signal passed into cell, phagocytose

53
Q

What is a bacterial cell coated with in bacterial opsonisation?

A

specific IgG

C3b

54
Q

In bacterial opsonisation what receptors recognise C3b and IgG?

A 
C3b = CR1
IgG = Fc receptors
55
Q

What happens after binding of C3b and IgG to their receptors?

A

internalised into a vesicle, dude with lysosome, lysosome contents release. lysis of cell.

56
Q

What is the Fc receptor present inmost cells called?

A

Fc (epsilon) R1 receptor

57
Q

When does the IgE bind to the Fc(epsilon) receptor?

A

allergic responses
(innocuous antigen)
cross-linked–> release inflammatory responses e.g histamine

Biomolecular Mechanisms (34 decks)

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