Lecture 6: B Cells and Antibodies

Question 1

draw an antibody with its heavy chains and light chains

Answer 1

check with fragment antigen binding site (FAB) and and fragment crystallisable region (Fc)

Question 2

which chains are constant and which are variable

Answer 2

• heavy chain is constant

- light chain is variable

Question 3

what is an epitope

Answer 3

a specific region on an antigen which interacts with an antigen binding site on an antibody. there are numerous epitopes on one antigen

Question 4

on which region do antibodies attach to B cells

Answer 4

Fc region

Question 5

how many types of antibody does each B cell produce?

Answer 5

just one, so all antibodies on the surface are he same

Question 6

what are the different antibody isotopes

Answer 6

• IgM
• IgA
• IgD
• IgG
• IgE

Question 7

IgM

Answer 7

• first antibody produced in immune response so present at birth
• has low affinity for antigens as it is immature
• forms pentamers which are held together by a joining chain (j chain)

Question 8

IgA

Answer 8

• the only antibody that can cross mucosal surfaces
• found in secretions, but protected from digestion by secretory component (s chain)
• forms dimers with a joining chain (j chain)
• colostrum, a forerunner of breast milk is rich in IgA

Question 9

IgD

Answer 9

like IgM is the first antibody produced by a B cell but has no known function

Question 10

IgG

Answer 10

main mature antibody form, circulates as a monomer

Question 11

IgE

Answer 11

• circulates as a monomer
• exact function not known but believed to be important in parasitic infection
• definitely important in allergies

Question 12

describe neutralisation by antibody

Answer 12

• antitoxin antibodies bind to the toxin directly and neutralise it
• eg clostridium tetani releases a toxin that causes muscle contraction (tetanus)

Question 13

describe receptor blocking by antibody

Answer 13

antibody binds to receptor on a virus so it can’t attch to host cell proteins

Question 14

describe opsonisation

Answer 14

coating of bacteria by circulating antibodies to enhance phagocytosis

Question 15

describe mast cell activation by antibodies

Answer 15

• mast cells found in the eye, skin, gut, lungs and nose
• have surface Fc receptors which get coated in IgE
• when the appropriate antigen binds to IgE and cross-links them, the mast cell “degranulates” releasing histamine
• inappropriately activated in allergy

Question 16

describe antibody-dependent cellular cytotoxicity

Answer 16

natural killer cells have Fc receptors on their surface which recognise antibody coated bacteria and kill them by non-phagocytotic means

Question 17

describe the complement response

Answer 17

• when an antibody interacts with an antigen it activates the complement system
• important for opsonisation, inflammation and terminal attack pathway

Question 18

how are antibody receptors generated

Answer 18

somatic recombination

Question 19

disadvantages of somatic recombination

Answer 19

• very energy intensive
• most receptors won’t be useful as they can’t fit biochemically or attack self antigens
• potential for autoimmune diseases as not all incorrect B cells can be destroyed properly

Question 20

describe clonal selection

Answer 20

• we all start with a unique set of B cells, a small number of each B cell
• when exposed to an antigen, the B cell that responds to it is stimulated to divide and produce antibodies

Question 21

describe class switch

Answer 21

when B cells divide in response to an antigen, IgM switches to IgG, so the variable region stays the same but heavy chain is swapped out

Question 22

describe somatic hypermutation

Answer 22

• random mutations are introduced to the variable region of the antibody so daughter cells produce a slightly different antibody
• some may have higher or lower affinity to the antigens
• those with higher affinity go through clonal selection
• these B cells become long-lived memory cells