Immunoglobulins

Question 1

Define antibody’s role

Answer 1

Glycoproteins secreted into serum in response to exposure to antigens

Question 2

What were the 4 fractions when electrophoresis was carried out on serum?

Answer 2

Albumin
Alpha, beta and gamma globulin

Question 3

Why were antibody molecules considered Gamma-globulins?

Answer 3

Most antibody activity is found in gamma fractions of the globulin

Question 4

What are the two functionally distinct fragments of antibodies?

Answer 4

Fab = fragment antigen-binding
Fc = fragment crystallizaable

Question 5

What are the functions of the distinct antibody regions?

Answer 5

Fab = antigen binding
Fc = effector function

Question 6

What enzyme was used to cleave the antibody, and what type of cleavage was it?

Answer 6

Papain proteolytically cleaved the antibody into 3 fragments

Question 7

Where does pepsin cleave the antibody?

Answer 7

Towards the C-terminal side of the disulphide bond
Splitting the antibody into Fab and Fc domains

Question 8

When cleaved what can fragment I and II still do?

Answer 8

Retain the power to combine with the antigen

Question 9

Properties of fragment III

Answer 9

Crystallizes easily
Has much of the antigenic specificity of the original molecule

Question 10

What causes the antibody to dissociate into Light and Heavy chains?

Answer 10

Reduction of the disulphide bonds in antibodies = occurs in presence of denaturing agents

Question 11

What are the molecular weights of L and H chains?

Answer 11

25kDa and 50kDa

Question 12

How many chains and what molecules weight is IgG?

Answer 12

2 LC and 2 HC = 150kDa

Question 13

What is the function of the hinge region?

Answer 13

Give flexibility
Create different bond angles between Ig arms

Question 14

Where is hypervariability found?

Answer 14

Primary amino acid sequence of V regions

Question 15

How are complementarity-determining regions formed?

Answer 15

3 hypervariable regions are separated in primary structure
CVD are formed when they come together in tertiary structure

Question 16

What is the complementarity-determining region?

Answer 16

Antigen binding site

Question 17

What separates the CDR?

Answer 17

Framework regions = highly conserved regions of the variable portion of the antibody

Question 18

How many CDRs are involved when antibody and antigen interact?

Answer 18

6

Question 19

What are Fr receptors?

Answer 19

Receptors on effector cells that bind antibodies’ Fc region

Question 20

What cells express receptors for antibodies?

Answer 20

Macrophages
Dendritic cells
Mast cells
Eosinophils
NK cells

Question 21

How many major types of light chains are there?

Answer 21

2 = kappa or lambda

Question 22

What are the 5 major genes that encode the heavy chains?

Answer 22

Gamma
Mu
Delta
Alpha
Epsilon

Question 23

What is special about the function of IgG?

Answer 23

Only IgG is transferred from mother to fetus
It is the only Ig that can cross the placenta

Question 24

When are there transient low levels of IgG?

Answer 24

2-4 months old
Disease susceptible period

Question 25

How do different subclasses occur?

Answer 25

Structural and functional differences

Question 26

Give examples of subclass structural differences

Answer 26

Different number of disulphide bonds Different size of hinge region

Question 27

Give examples of different physiochemical properties of IgG subclasses

Answer 27

Serum concentrations Serum half lives

Question 28

What form is IgA present in the serum (circulation)?

Answer 28

Monomeric

Question 29

What form is IgA present in secretion?

Answer 29

Dimeric

Question 30

What is the function of the J chain?

Answer 30

J chain regulates the multimerization of IgM and IgA in mammals

Question 31

What does the antibody isotype determine?

Answer 31

Effector function

Question 32

What are the 5 effector functions?

Answer 32

1. Antibody dependent cellular cytotoxicity (ADCC) 2. Degranulation of mast cells and eosinophils 3. Opsonization of pathogens 4. Recruitment of complement 5. Neutralization of bacteria, viruses and toxins

Question 33

What are the functions of antibodies and how is this function carried out?

Answer 33

Protect us by recruiting other effector functions Through interaction of Fc with other cells

Question 34

How do antibodies neutralize viruses?

Answer 34

Antibodies bind to the viruses, preventing the virus from binding to cell surface receptors Blocks fusion event

Question 35

Which antibodies neutralize toxins?

Answer 35

IgA and IgG

Question 36

How can we protect against toxic effects of venom?

Answer 36

Passive immunization

Question 37

What is antibody opsonization?

Answer 37

Process by which a pathogen is marked for phagocytosis

Question 38

How does opsonization enhance pathogen killing?

Answer 38

C3b binds CR1 receptor on effector cell

Question 39

What must occur to cross-link with Fc receptors on effector cells?

Answer 39

Antibody must be bound to antigen on pathogen = this allows Fc receptors on effector cell to bind the complex

Question 40

What cells mainly use antibody dependent cellular cytotoxicity?

Answer 40

NK cells

Question 41

What is antibody dependent cellular cytotoxicity?

Answer 41

The activation of NK cells by antibodies binding to its Fc receptor and binding to pathogen NK then releases the enzyme perforin that punches holes in the pathogen, causing it to lyse

Question 42

What antibodies recruits eosinophils?

Answer 42

IgE

Question 43

What do eosinophils mainly attack?

Answer 43

Parasites

Question 44

How is degranulation activated?

Answer 44

IgE coats the parasite and eosinophil binds IgR through Fc receptor Eosinophil degranulates and releases lysozymes and cytotoxic granules