b cells and antibodies

Question 1

What is part of the ‘adaptive’ immune system?

Answer 1

antibodies and T cells

Question 2

What part of antigens do antibodies actually recognise?

Answer 2

epitopes

Question 3

What does the Fc region of antibodies do?

Answer 3

interacts with other cells and molecules of the immune system

Question 4

What are the 5 antibody isotypes?

Answer 4

• IgM
• IgD
• IgA
• IgG
• IgE

Question 5

Describe the IgM response?

Answer 5

• first antibody produced in immune response
• low affinity for antigen
• forms ‘pentamers’, held together by joining (j) chain

Question 6

Describe IgA

Answer 6

• only antibody that can cross mucosal surfaces
• found in secretions (colostrum rich in this)
• protected from digestion by secretory component (s chain)
• forms dimers (joining j chain)

Question 7

Describe IgD

Answer 7

• like IgM, first antibody produced by B cell
• but no known function

Question 8

Describe IgG

Answer 8

• main mature antibody form
• circulates as a monomer

Question 9

Describe IgE

Answer 9

• circulates as monomer
• exact function not known (believed to be important for parasitic infection)
• defo important in allergic disease

Question 10

What are the 3 ways antibodies can help us?

Answer 10

• by binding to things and affecting them
• by binding to things and interacting with another element of the immune system
• when bound to b cells: act as receptors

Question 11

What are the ways antibodies can bind to things and affect them?

Answer 11

• toxin neutralisation
• receptor blocking

Question 12

What are the ways antibodies can bind to things and interact with another element of the immune system?

Answer 12

• phagocytes (opsonisation)
• mast cell activation
• complement
• antibody-dependent cellular cytotoxicity

Question 13

How do antibodies aid in opsonisation?

Answer 13

1. bacteria coated by antibody
2. phagocytic cells have receptors for Fc portion of antibody
3. enhances phagocytosis by reducing repulsion between two negatively charged membranes

Question 14

How do antibodies aid in mast cell activation?

Answer 14

1. mast cells coated with IgE antibody (has Fc receptor)
2. when appropriate antigen binds IgE antibodies, mast cell ‘degranulates’, releasing histamine

Question 15

How do antibodies aid in antibody-dependent cellular toxicity?

Answer 15

1. NK cell recognises antibody-coated bacteria by Fc receptor
2. target organism then killed by non-phagocytic means

Question 16

How do antibodies aid in interaction with ‘complement’?

Answer 16

activates complement system:
1. opsonisation
2. inflammation
3. terminal attack pathway

Question 17

What is the principle of receptor generation by somatic recombination

Answer 17

select gene segment from region 1, 2 and 3 at random and combine them to make variable region of antibody

Question 18

What is clonal selection?

Answer 18

division and selection of the fittest B cells

Question 19

What are the two things B cells do when they divide?

Answer 19

• class switch
• somatic hypermutation

Question 20

What is the class switch that happens during B cell divison?

Answer 20

• IgM in primary response switches to IgG
• variable region of antibody remains the same though

Question 21

What is somatic hypermutation that happens during B cell divison?

Answer 21

• random mutations introduced into variable region
• daughter cells therefore produce slightly different antibody
• further clonal selection pick out best receptors

Question 22

What is the primary immune response?

Answer 22

1. low affinity IgM antibody meets antibody
2. class switch or somatic hypermutation

Question 23

What is the secondary immune response?

Answer 23

1. best B cells now selected and number increased
2. these mature B cells become memory cells and respond vigorously when stimulated again (a lot of IgG)