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Immunuology > Immunoglobulin structure and fucntion > Flashcards

Immunoglobulin structure and fucntion Flashcards

1
Q

what are antibodies also termed as?

A

immunoglobulins

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2
Q

where are immunoglobulins present in?

A

Plasma, tissues, secretions and lymphatics

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3
Q

what is immunoglobulins a product of?

A

humoral immune system

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4
Q

what are immunoglobulins secreted by?

A

activated B cells

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5
Q

What are the five classes of immunoglobulin?

A
  • IgG
  • IgM
  • IgA
  • IgD
  • IgE
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6
Q

what do these 5 classes of immunoglobulins do?

A

Provide recognition function and trigger effector functions

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7
Q

Describe the structure of an antibody molecule.

A

Consists of two heavy chains and two light chains. The hinge that connects the two heavy chains is disulphide bonds and non covalent interactions also hold chains together

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8
Q

what do both the heavy and Light chains have?

A
  • variable region

- constant region

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9
Q

what does the Fab region stand for?

A

fragment antigen binding

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10
Q

what does the Fc region stand for?

A

fragment crystaliasble

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11
Q

Relate Fab and Fc regions to the dual function of antibodies.

A
  • Recognition function- Binding to antigen via Fab arms

- Effector function- Clearance mechanisms via interaction of Fc with effector molecules

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12
Q

what are the two types of light chains?

A
  • lambda

- Kappa

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13
Q

Do light chains in antibodies classes differ?

A

No -All antibody classes use these same light chains

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14
Q

what do the light chains fold up into?

A

2 globular domains termed VL and CL

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15
Q

What determines the class of antibody?

A

the heavy chains

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16
Q

Name the different heavy chains in the 5 classes.

A 
IgG	gamma  heavy chain
IgA	 alpha heavy chain
IgM	 micro heavy chain
IgE.  epsilon heavy chain
IgD 	 delta heavy chain
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17
Q

what does the heavy chains fold up into?

A

-IgG , IgA, IgD into 4 globular domains and for IgM and IgE 5 globular domains

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18
Q

what is needed for antibody molecules to complete their effector function?

A

sugar attachments - oligosaccharides

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19
Q

With millions of different antigens, what do antibodies do (adapter molecules)?

A

produce small number of effector molecules

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20
Q

what was revealed when comparing sequences of different antibodies?

A

There were three hypervariable loops or CDRs (complementarity determining region) in each V domain

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21
Q

what do hyper variable loops or CDRs form?

A

antigen binding site

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22
Q

What happens when Vh (variable heavy domain) and Vl (variable light domain) are paired?

A

their 6 CDRs create the antigen-binding site

23
Q

what makes up the antigen binding site?

A

6 Hypervariable regions or complementarity determining regions (CDR) - 3 in VH and 3 in VL

24
Q

how does the antigen binding site and antigen bind?

A

Complementarity of 3D structures

25
Q

What is the most abundant Ig in plasma?

A

IgG

26
Q

Describe the shape of the IgG?

A

Y shaped:

2 HC of 50 kDa, 2 LC of 25 kDa

27
Q

What are the subclasses of IgG?

A

4 subclasses - IgG1, IgG2, IgG3, IgG4

28
Q

what is IgG efficient at triggering?

A

complement and phagocytosis via Fc receptors

29
Q

what characteristic does IgG have that no other Ig’s have?

A

Only Ig class to cross placenta from mother to foetus - protects baby in first months of life

30
Q

what is IgG a predominant antibody of?

A

Secondary response

31
Q

where is IgM found?

A

Only in plasma and secretions as it is too large to enter tissues

32
Q

Describe the structure of IgM.

A

5 Y-shaped units:
Joined by J chain and disulphide bridges
Heavy chain has 5 globular domains

33
Q

How many binding sites does IgM have for antigens?

A

10 binding sites -very good at

agglutinating particles eg viruses

34
Q

what is IgM efficient at doing?

A

activating complement

35
Q

What is IgM a predominant antibody of?

A

Primary response

36
Q

what is Iga the major antibody in?

A

seromucous secretions

e.g. salvia, milk

37
Q

what is IgA first to encounter?

A

invading bacteria and viruses

38
Q

what are the 2 subclasses of IgA?

A

IgA1 and IgA2

39
Q

what are the two forms of IgA?

A

Monomeric and dimeric forms

40
Q

what percentage of IgA subclasses are in the monomeric form?

A

90% IgA1, 10% IgA2

41
Q

what percentage of IgA subclasses are in the dimeric form?

A

40% IgA1, 60% IgA2

42
Q

what form of IgA is serum?

A

monomeric

43
Q

what form of IgA is secretory?

A

predominantly dimeric

44
Q

why does IgA1 have more O-linked sugars than IgA2?

A

IgA1 has a long hinge and so needs more protection

45
Q

what antibody is heavily glycosylated?

A

IgE

46
Q

what is IgE’s effector function?

A

Interacts with FcRI:

  • High affinity receptor
  • Expressed on mast cells and basophils
  • Associated with allergic response
47
Q

what IgE important for?

A

important against parasitic infections

48
Q

What is the serum concentration of IgD?

A

very low

49
Q

where are IgD found?

A

surface of lymphocytes

50
Q

what are Fc receptors?

A

receptors which bind specifically to the Fc region of immunoglobulins

51
Q

what immune cells are Fc receptors present on?

A
  • macrophages
  • neutrophils
  • basophils,mast cells
52
Q

what can binding of antibody-coated targets to FcR on immune cells result in?

A

A) Phagocytosis
B) Release of activated oxygen species and enzymes
C) Release of inflammatory mediators e.g. histamine (via FcRI)
D) Enhanced antigen presentation
E) Clearance of immune complexes

53
Q

when an antibody-Fc receptor complex binds to allergens, what is released from the mast cell as a result?

A

Release of histamine, prostaglandins,

leukotrienes and other mediators of allergic response

Immunuology (10 decks)

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