Lecture 29

Question 1

Structure of Antibody

Answer 1

• Y shaped glycoprotein
• A part of Immunoglobulin family
• 2 identical disulfide linked heavy chains and 2 identical light chains
• 4 chains total

Question 2

Where are Variable regions

Answer 2

At tip/top of Y
Both heavy and light chain have a variable region
Light chain–>VL
Heavy chain–> VH

Question 3

Where is constant region

Answer 3

Base and cross of Y
Both heavy and light chains have a constant region
Light chain–>CL
Heavy chain–>CH

Question 4

Function of Variable region

Answer 4

Antigen Binding
VL and VH forms antigen-binding sites (2 identical sites per antibody, one at each tip of Y)
Binding can result in neutralization

Question 5

Function of Constant regions

Answer 5

Involved in complement activation
Constant region (Fc) can bind to Fc receptors on phagocytes and other cell types (mast cells and eosinophils)

Question 6

Fab fragment contents

Answer 6

2 Fab fragments per antibody
Each fragment has an antigen-binding domain AND part of CH and CL chains
Each Fork of Y
Fab= fragment antigen binding

Question 7

Fc fragment contents

Answer 7

1 Fc fragment
Constant region of heavy chain
Receptors that bind antibodies recognize the Fc region
Base of Y
Fc= fragment crystallizable

Question 8

Immunoglobulin contents

Answer 8

2 Heavy chains (each with variable and constant regions)
2 Light chains (each with variable and constant regions)

Question 9

How are heavy and light chains held together

Answer 9

By intra/interchain disulfide covalent bonds
Both constant and variable regions are folded in complex 3D structures including beta strands

Question 10

Where is the Complementarity determining region (CDR)

Answer 10

In Variable region of light chain at extremities (very tip of fork)

Question 11

CDR contents

Answer 11

6 Hypervariable loops (3 loops per variable domain)
Not part of the beta strands

Question 12

Function of CDR

Answer 12

Allows for antigen specificity
Has direct contact with antigen (being part of the antigen binding site)
Greatest variability in antibody sequence

Question 13

Types of bonds for antigen binding

Answer 13

Involves non-covalent bonding between the immunoglobulin and antigen epitope
Ex. Hydrogen bonds, Van der Waals, Hydrophobic, Ionic bonds

Question 14

Saying for antigen binding specificity

Answer 14

Lock and key specificity
- involves extremities of antibody (CDR)
Location of epitopes can be anywhere on the antigen

Question 15

5 Major classes of antibody

Answer 15

IgG, IgA, IgM, IgE, IgD

Question 16

How are antibody classes different

Answer 16

1)Different number of Ig-like domains
2) Different length of constant region in heavy chains (different amino acid sequence)
3) Different functions during immune response

Question 17

Overall structure of IgM

Answer 17

1) Pentameric (5 antibodies linked together via disulphide bonds)
2) Heavy chain has 4 constant regions and 1 variable region

Question 18

When are IgM expressed

Answer 18

Mature B cells prior to activation (transmembrane expression)

Question 19

Which immunoglobulins are part of the first wave of secreted antibodies

Answer 19

IgM, IgD

Question 20

What is immunoglobulin the most effective initiator of the complement cascade

Answer 20

IgM

Question 21

IgD structure

Answer 21

Heavy chain has 3 constant regions and 1 variable region

Question 22

IgG structure

Answer 22

Heavy chain has 3 constant regions and 1 variable region
4 subclasses in humans IgG (1-4)

Question 23

Which immunoglobulin is most abundant in plasma

Answer 23

IgG

Question 24

When are IgG produced

Answer 24

Following differentiation in the Germinal Center

Question 25

IgE structure

Answer 25

Heavy chain has 4 constant regions and 1 variable region

Question 26

When are IgE produced

Answer 26

In response to Helminth infections
IgE role in TH2 response

Question 27

Structure of IgA

Answer 27

Heavy chains has 3 constant regions and 1 variable region
In plasma–>monomer
In mucous secretions through the J chain–>dimer
2 subclasses: IgA1 and IgA2

Question 28

Which immunoglobulin is important for mucosal immunity

Answer 28

IgA

Question 29

Treatment for rheumatoid arthritis

Answer 29

Antibody against TNF-alpha (pro-inflammatory cytokine)

Question 30

Clinical use of antibodies

Answer 30

1) Antibodies made to bind virtually any epitope
2) Antibody made to bind to another antibody