4. Immunoglobulin Classes- Structure and Function Part I

Question 1

What Greek letters denote the heavy and light chains in the IgG molecule?

Answer 1

Heavy chains: Gamma, Alpha, Mu, Delta, or Epsilon

Light chains: Kappa or Lambda

Question 2

What portion of the IgG molecule is responsible for binding to antigen? binding to complement? binding to macrophages?

Answer 2

Antigen = binds to variable region (NH2 Terminal) at their epitope
Macrophage = binds to IgG at their constant region with their Fc receptor
Complement = binds to 2 IgG at their constant region

Question 3

What is the difference between affinity and avidity?

Answer 3

Affinity = force of attraction between a SINGLE Ag-binding site on the Ab, and the Ag.

Avidity = sum of ALL attractive forces between an Ag and an Ab

Question 4

What fragments result from treatment of the IgG molecule with papain? with pepsin?

Answer 4

Papain = Fab x2 and FC
Pepsin = F(ab')2 and Fc fragments

Question 5

What chemical reduces the disulfide bonds of an immunoglobulin molecule so it is broken down into its heavy and light chains?

Answer 5

Mercaptoethanol

Question 6

What is opsonization, and which IgG subclasses can serve as opsonins?

Answer 6

Opsonization is the enchancement of phagocytosis by coating the Ags with opsonins

IgG opsonins = IgG1 & IgG3

Question 7

What cells does IgG bind to in the process of ADCC?

Answer 7

• NK cells
• Macrophages
• PMN (polymorphonuclear cells)

Question 8

How does IgG protect the infant during the first few months of life if the infant produces little IgG during that time period?

Answer 8

IgG is the only immunoglobulin that can cross the placenta from mother to infant in order to protect the newborn during the 1st few months of life. IgG1 and IgG4 (best) mediate this.