L5 - Ig Structure

Question 1

How many Ig domains does each heavy chain have on the Fc region in secreted IgG?

Answer 1

2

Question 2

Approximately how many amino acids long are Ig domains?

Answer 2

~110

Question 3

What happens to an antibody during proteolytic cleavage by papain?

Answer 3

Cleavage at the hinge region resulting in 2 x Fab region and an Fc region

Question 4

What happens to an antibody during proteolytic cleavage by pepsin?

Answer 4

Cleavage below the hinge resulting in a F(ab’)2 region and a pFc’ region. Can still neutralize via functional Fab portion

Question 5

What are the 5 Ig isotypes?

Answer 5

IgA, IgD, IgG, IgE and IgM

Question 6

What is the most abundant / least abundant Igs?

Answer 6

Most abundant: IgG

Least abundant: IgE

Question 7

What are some properties of IgG?

Answer 7

• Found in serum and lymph
• Monomer, major class in secondary response
• High affinity

Question 8

What are some properties of IgM?

Answer 8

• Found in serum
• Has an extra C domain
• Pentamer
• High avidity but low affinity
• J chain

Question 9

What are some properties of IgA?

Answer 9

• Found in serum and secretions
• Dimer
• Major Ig secreted into GI and respiratory tract
• Uses secretory component for transcytosis into lumenal space
• J chain

Question 10

What are some properties of IgE?

Answer 10

• Found beneath epithelial surfaces
• Involved in allergic reactions, involved in response in parasites
• Binds to mast cells
• Has extra C domain

Question 11

What are some antibody effector functions?

Answer 11

• Neutralization
• Opsonization
• Complement activation

Question 12

What is meant by direct mechanism vs indirect with regards to neutralization via antibodies?

Answer 12

Direct - Involves Fab part of Ig

Indirect - Involves Fc part of Ig

Question 13

What is ADCC?

Answer 13

Antibody-dependent cell mediated cytotoxicity

• Ab binds to target cell via Fab region
• Ab binds to NK cell via Fc region / FcgRIII receptor (CD16)
• Cross linking of FcR triggers NK cell killing

Question 14

What triggers degranulation in eosinophils or mast cells?

Answer 14

IgE binds to parasite or allergen, which via its Fc region binds to FceR on Mast cells
- Cross linking of FceR triggers degranulation e.g. histamine

Question 15

Briefly discuss the beginning of complement activation via antibodies

Answer 15

• Ab binds to C1q via Fc initiating the classical complement cascade