Immunoglobulin structure and fucntion

Question 1

what are antibodies also termed as?

Answer 1

immunoglobulins

Question 2

where are immunoglobulins present in?

Answer 2

Plasma, tissues, secretions and lymphatics

Question 3

what is immunoglobulins a product of?

Answer 3

humoral immune system

Question 4

what are immunoglobulins secreted by?

Answer 4

activated B cells

Question 5

What are the five classes of immunoglobulin?

Answer 5

• IgG
• IgM
• IgA
• IgD
• IgE

Question 6

what do these 5 classes of immunoglobulins do?

Answer 6

Provide recognition function and trigger effector functions

Question 7

Describe the structure of an antibody molecule.

Answer 7

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

Question 8

what do both the heavy and Light chains have?

Answer 8

• variable region

- constant region

Question 9

what does the Fab region stand for?

Answer 9

fragment antigen binding

Question 10

what does the Fc region stand for?

Answer 10

fragment crystaliasble

Question 11

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

Answer 11

• Recognition function- Binding to antigen via Fab arms

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

Question 12

what are the two types of light chains?

Answer 12

• lambda

- Kappa

Question 13

Do light chains in antibodies classes differ?

Answer 13

No -All antibody classes use these same light chains

Question 14

what do the light chains fold up into?

Answer 14

2 globular domains termed VL and CL

Question 15

What determines the class of antibody?

Answer 15

the heavy chains

Question 16

Name the different heavy chains in the 5 classes.

Answer 16

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

Question 17

what does the heavy chains fold up into?

Answer 17

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

Question 18

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

Answer 18

sugar attachments - oligosaccharides

Question 19

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

Answer 19

produce small number of effector molecules

Question 20

what was revealed when comparing sequences of different antibodies?

Answer 20

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

Question 21

what do hyper variable loops or CDRs form?

Answer 21

antigen binding site

Question 22

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

Answer 22

their 6 CDRs create the antigen-binding site

Question 23

what makes up the antigen binding site?

Answer 23

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

Question 24

how does the antigen binding site and antigen bind?

Answer 24

Complementarity of 3D structures

Question 25

What is the most abundant Ig in plasma?

Answer 25

IgG

Question 26

Describe the shape of the IgG?

Answer 26

Y shaped: | 2 HC of 50 kDa, 2 LC of 25 kDa

Question 27

What are the subclasses of IgG?

Answer 27

4 subclasses - IgG1, IgG2, IgG3, IgG4

Question 28

what is IgG efficient at triggering?

Answer 28

complement and phagocytosis via Fc receptors

Question 29

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

Answer 29

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

Question 30

what is IgG a predominant antibody of?

Answer 30

Secondary response

Question 31

where is IgM found?

Answer 31

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

Question 32

Describe the structure of IgM.

Answer 32

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

Question 33

How many binding sites does IgM have for antigens?

Answer 33

10 binding sites -very good at | agglutinating particles eg viruses

Question 34

what is IgM efficient at doing?

Answer 34

activating complement

Question 35

What is IgM a predominant antibody of?

Answer 35

Primary response

Question 36

what is Iga the major antibody in?

Answer 36

seromucous secretions | e.g. salvia, milk

Question 37

what is IgA first to encounter?

Answer 37

invading bacteria and viruses

Question 38

what are the 2 subclasses of IgA?

Answer 38

IgA1 and IgA2

Question 39

what are the two forms of IgA?

Answer 39

Monomeric and dimeric forms

Question 40

what percentage of IgA subclasses are in the monomeric form?

Answer 40

90% IgA1, 10% IgA2

Question 41

what percentage of IgA subclasses are in the dimeric form?

Answer 41

40% IgA1, 60% IgA2

Question 42

what form of IgA is serum?

Answer 42

monomeric

Question 43

what form of IgA is secretory?

Answer 43

predominantly dimeric

Question 44

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

Answer 44

IgA1 has a long hinge and so needs more protection

Question 45

what antibody is heavily glycosylated?

Answer 45

IgE

Question 46

what is IgE's effector function?

Answer 46

Interacts with FcRI: - High affinity receptor - Expressed on mast cells and basophils - Associated with allergic response

Question 47

what IgE important for?

Answer 47

important against parasitic infections

Question 48

What is the serum concentration of IgD?

Answer 48

very low

Question 49

where are IgD found?

Answer 49

surface of lymphocytes

Question 50

what are Fc receptors?

Answer 50

receptors which bind specifically to the Fc region of immunoglobulins

Question 51

what immune cells are Fc receptors present on?

Answer 51

- macrophages - neutrophils - basophils,mast cells

Question 52

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

Answer 52

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

Question 53

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

Answer 53

Release of histamine, prostaglandins, | leukotrienes and other mediators of allergic response