Lecture 4, IG Structure

Question 1

What are the 5 Ig isotypes?

Answer 1

IgM, IgG, IgE, IgA, IgD

Question 2

Describe the structure of an Ig

Answer 2

2 central heavy chains, each w/ a light chain attachment via di-S bonds.
- All 4 chains have a variable and constant domain

Question 3

What’s another name for the hyper-variable regions of each chain?

Answer 3

CDR: complementarity-determining region

Question 4

In the CDR, 3 hyper-variable regions combine to make a _______________.

Answer 4

Binding site

Question 5

If treated w/a proteolytic enzyme, what would be the names of the resulting Ig fragments?
*Which would tell you what class of Ig it is?

Answer 5

• Fab (ag-binding fragment)
• Fc (crystallizable fragment- constant region)
  Fc would tell you Ig class

Question 6

Which Ig’s aren’t only found in monomeric form, and what form are they found in?
What’s the name of their accessory protein, in each?

Answer 6

• Pentameric IgM
• Dimeric IgA
  (both contain J chain as well)

Question 7

If you see cell w/monomeric IgM on its surface, by definition it’s a _____________.

Answer 7

B cell

Question 8

What’s an epitope?

About how many AA’s long do they span?

Answer 8

Antigenic determinant (small segment of ag where AB binds)
- Usually 6-8 AAs long (so can be lots)

Question 9

IgA in the mucosa is found as a ___________ but in the serum it’s found as a ___________.

Answer 9

• dimer

- monomer

Question 10

What is the major AB of the body? Where is it mostly found?

Answer 10

IgA

- Mucosa

Question 11

What’s the major AB of the blood?

Answer 11

IgG

Question 12

What is the normal laboratory value of serum total protein?

What portion is Ig?

Answer 12

• 7 g/dL (wiki; but she says 100…)

- Ig: ~1/10th of the total protein found in blood (mostly IgG)

Question 13

What’s the 1/2-life range of the Ig’s?

*Which typically has the longest 1/2-life?

Answer 13

~2-21 days

- IgG

Question 14

Cross-linking of which Ig on mast cell leads to degranulation? (allergies)

Answer 14

IgE

Question 15

What’s the name of the receptors that cells have to bind Ig’s?
Which part of the Ig do they bind?

Answer 15

Fc receptors (e.g. Fc-epsilon, Fc-gamma, etc)
- Bind constant domain

Question 16

By which 3 Methods do ABs mediate humoral immunity?

Answer 16

1. Neutralization
2. Opsonization (facilitates phagocytosis)
3. Complement Activation (phagocytosis facilitated, sometimes w/lysis)

Question 17

What must happen when an Ig binds an Fc in order for a response to occur?

Answer 17

Cross-linking

Question 18

Prior to conception, fetus relies on what Ig from mom?
Fetus first starts to develop which of its own Ig’s?
What 2 come next, after birth?

Answer 18

• IgG
• IgM
• IgG, IgA

Question 19

The total 1/2-life of AB’s to diseases like tetanus and measles is:

a. weeks
b. months
c. years

Answer 19

c. years

5-10 years for tetanus, 3,000 years for measles

Question 20

AB from a clone of B cells is ___________. AB from multiple clones of B cells is ___________.

Answer 20

• Monoclonal

- Polyclonal

Question 21

What is IVIG?

How is it made?

Answer 21

• Intravenous immunoglobulin: Polyclonal AB used to treat many immune deficiencies and inflammatory dz’s
• Made by taking serum from ~10K different people, isolate the serum, pool together (not known if it actually works)

Question 22

Class-specific antigenic determinants are associated w/which part of the Ig molecule?

Answer 22

Constant region of heavy chain

Question 23

How do you differentiate a T from B cell?

What about a specific type of B cell?

Answer 23

B cells have IgM on the surface.

- Could also look for kappa or lamba light chain to find a specific type of B cell?

Question 24

What’s the major AB in secretions (saliva, tears, breast milk)?
Be specific

Answer 24

Mucosal IgA (dimeric)

Question 25

First serum AB made in an immune response?

Answer 25

IgM

Question 26

What Ig plays a primary role in protecting gut or resp mucosa?

Answer 26

Secratory IgA

Question 27

Predominant Ig produced in the primary immune response?

Answer 27

IgM

Question 28

Predominant Ig produced in the secondary immune response?

Answer 28

IgG

Question 29

Predominant Ig in external secretions as dimer? (monomer in the serum)

Answer 29

IgA

Question 30

Ig found mainly on surface of B cells, only?

Answer 30

IgD

Question 31

Ig involved in allergic hypersensitivities?

Answer 31

IgE

Question 32

What major Ig crosses placental barrier?

Which 2 others major ones don’t?

Answer 32

• IgG does

- IgM, IgA don’t

Question 33

What Ig has a role in mucosal immunity, but it’s fcn is unclear?

Answer 33

IgA

Question 34

*Compare the relative levels of each Ig class in serum.

Answer 34

IgG 13.5mg/dL > IgA 2.1 > IgM 1.5 > IgD 0.04 > IgE 3E-5