B cells and antigen recognition

Question 1

Where do B lymphocytes differentiate?

Answer 1

Bone marrow

Question 2

What is the major function of B lymphocytes?

Answer 2

To produce antibodies

Question 3

What can antibodies bind to?

Answer 3

• proteins
• polysaccharides
• small molecules such as toxins

Question 4

How many different constant regions are there?

Answer 4

5

Question 5

What does papain cleave antibodies into?

Answer 5

Fc and Fab

Question 6

What are the 5 different isotypes of Ig?

Answer 6

• IgM
• IgG
• IgA
• IgE
• IgD

Question 7

Which Ig isotype is never secreted?

Answer 7

IgD

Question 8

Which Ig isotypes are found in the plasma?

Answer 8

IgG and IgM

Question 9

Which Ig isotype is found in extracellular fluid and crosses the placenta?

Answer 9

IgG

Question 10

Which Ig is mainly found in secretions?

Answer 10

IgA

Question 11

What are the characteristics of IgM?

Answer 11

• Produced 1st in response
• Pentamer
• Effective first defence against bacteria
• Fairly low affinity

Question 12

What are the characteristics of IgG?

Answer 12

• Produced late in the immune response
• Most abundant
• Crosses the placenta

Question 13

How many subtypes of IgG are there?

Answer 13

4

Question 14

What are the characteristics of IgA?

Answer 14

• Produced late in the immune response
• Can exist as monomers or dimers
• Major Ig in secretions

Question 15

Which Ig is involved in the response to parasitic infections?

Question 16

What does IgE do?

Answer 16

Induces degranulation of mast cella and basophils

Question 17

What are the characteristics of IgD?

Answer 17

• Found as a receptor on the surface of naive lymphocytes
• Not secreted
• Function unknown

Question 18

Which type of BCRs are found on naive B cells?

Answer 18

IgM and IgD

Question 19

What happens when B cells encounter an antigen for the 1st time?

Answer 19

It proliferates massively

Question 20

How are effector cells different to naive cells?

Answer 20

They are already class switched and quicker at reaching pathogens

Question 21

What does isotype switching involve?

Answer 21

Changing the C domain of the heavy chain at DNA level

Question 22

What are the 3 major functions of antibodies?

Answer 22

• Neutralization
• Opsonization
• Complement fixation

Question 23

What are the 2 ways antibodies complete neutralisation?

Answer 23

• Prevents bacteria and viruses from adhering to and infecting cells
• Binding to toxins prevents cell damage

Question 24

Why is neutralisation specifically important in response to viruses/intracellular bacteria?

Answer 24

Blocks internalisation

Question 25

What is opsonization?

Answer 25

Where antibodies coat a bacteria to promote phagocytosis

Question 26

How does opsonization demonstrate a link between the adaptive and innate immune systems?

Answer 26

The coating of anitbodies enhances the action of the innate immune system (and phagocytosis) by extending recognition repetoir

Question 27

How does opsonization enhance the immune response?

Answer 27

* Promotes phagocytosis * Activates natural killer cells

Question 28

What is complement?

Answer 28

A blood-borne group of proteins that form a proteolytic cascade in response to pathogen recognition

Question 29

Is complement part of the innate or adaptive immune response?

Answer 29

Innate

Question 30

What triggers the complement pathway?

Answer 30

Antibody-antigen complexes

Question 31

What are the 2 ways innate immune cells can be activated?

Answer 31

* Activation of pattern recognition receptors as part of innate function * Activation of receptorsfor antibodies that are produced as part of the adaptive immune response

Question 32

How does complement kills pathogens?

Answer 32

It forms pores in the membranes to premealise the cell

Question 33

What is isotype switching?

Answer 33

The process by which the C domain of the heavy chain of an antibody is changed at the DNA level in order to change the class of immunoglobulin a particular antibody is

Question 34

Where does isotype switching occur?

Answer 34

In germinal centres in lymph nodes

Question 35

What do C3a and C5a do?

Answer 35

Powerful initiators of effector function

Question 36

What does C3b do?

Answer 36

It can label bacteria (provides an alternative to opsonisation

Question 37

What are the 2 effector functions of complement?

Answer 37

* Can label bacteria * Forms a membrane attack complex

Question 38

Outline the general principles of how complement works

Answer 38

* Complement proteins are activated by microbial surfaces or antibody-antigen complexes * This leads to the formation of proteases * Soluble factors are released * Membrane attack complex is formed