Lecture 9

Question 1

What are the features of IgM

Answer 1

• Has a high valency
  Has 10 FAB arms so can bind lots of antigen at once
  -Good at activating complement

Question 2

Structure of immunoglobulin a

Answer 2

The heavy chain is an alpha chain. Can occur as a monomer in serum or as a dimer

Question 3

What can IgA bind to

Answer 3

Can bind to another form of an Fc receptor (one found in gut epithelia) - relates to the way IgA gets from lymphoid tissue to where its needed in secretions

Question 4

Structure of IgD

Answer 4

Its a monomer (single Y shaped antibody unit), doesn’t have a proper hinge region but an extra pair of domains. The domains are flexible and bend through a functional hinge.

Question 5

What’s IgD’s main role

Answer 5

Defence against large extracellular parasites e.g. helminths.

Question 6

Why are antibodies referrred to as flexible adaptors

Answer 6

1. Function to bind to antigen which is mediated by FAB arms
2. Effector functions which are mediated by Fc regions because they can plug into different elements of the immune system

Question 7

Biological role of immunoglobulins

Answer 7

1. Agglutinate particles e.g. bacteria (IgM, IgA)- more easily removed from body by peristalsis
2. Can also form immune complexes with soluble antigen - easier to the body to get rid of as they bind to Fc receptors
3. Block binding pathogens to host cells (IgA, IgG)
4. They neutralise toxins e.g. tetanus
5. They immobilise pathogens e.g. flagella

Question 8

What are the functions of Fc effectors

Answer 8

They invoke destruction of labelled pathogens, they can activate complement.

Question 9

NB effector mechanisms that operate depend on what two things

Answer 9

1.Site and type of infection
2. Stage of the immune response (primary or secondary)

Question 10

What are C1S and C1R

Answer 10

They are serine proteases and they cleave proteins

Question 11

How do you activate complement

Answer 11

C1Q needs to bind to adjacent antigens on the surface of a bacteria.

For activation, at least two of the tulip heads need to bind to antibody.

C1Q must interact with the 2 Fc regions for activation to occur.

Question 12

What happens when antibodies bind to antigen

Answer 12

1. They interact with C1Q causing a confirmational change associated with serum proteases
2. When C1R is activated, it cleaves C1S which activates it to a protease
3. C1S can act on C4 and C2 which are both cleaved. This generates a C3 convertase