INTRO TO B CELLS AND ANTIBODIES

Question 1

what are B cells?

Answer 1

Stay in the lymphatic tissue and respond to antigens by differentiating into plasma cells

Question 2

how are B cells activated?

Answer 2

by B cell receptors (BCRs) binding to specific antigens

Question 3

what do B cells respond to?

Answer 3

to either unprocessed antigens or antigens presented by antigen presenting cells
initially respond to foreign antigens by taking in some of the antigen molecule, and then combining antigen fragments to MHC –II

Question 4

what is the antigen-MHC-II complex recognised by?

Answer 4

by helper T cells which secrete cytotokines i.e. IL-2, IL-4, IL-6

Question 5

what do cytokines do?

Answer 5

co-stimulate the B cells

Question 6

what happens once B cells are activated?

Answer 6

some of the B cells enlarge and differentiate into plasma cells which secrete antibodies that are specific to the initial stimulating antigen.
Some become memory B cells.

Question 7

what is the structure of an antibody?

Answer 7

consist of 4 polypeptide chains, two identical heavy chains and two identical light chains

Question 8

what is the heavy chain made of?

Answer 8

of about 450 AA and also some additional carbohydrate chains

Question 9

what is the light chain made of?

Answer 9

only consist of about 220 AA

Question 10

how is the light chain bound o the heavy chain?

Answer 10

by a disulfide bond

Question 11

how are the 2 heavy chains held together?

Answer 11

at the mid region by 2 disulphide bonds which forms the hinge region of the antibody

Question 12

what forms beyond the hinge region on the heavy chains?

Answer 12

a common stem region

Question 13

what 2 regions do both the light and heavy chain possess?

Answer 13

variable regions and the constant regions (V and C regions)

Question 14

what is the V region?

Answer 14

confer the specificity of the antibody

Question 15

where are the V region found?

Answer 15

at the tips of the H and l chains at the apex of the antibodies arms

Question 16

how many binding sites does each antibody have?

Answer 16

2

Question 17

what does the flexibility of the hinge region allow?

Answer 17

allows the 2 recognition sites to bind to quite widely separated antigens

Question 18

what is the C region?

Answer 18

consists of those regions of the H and L chains not associated with antigen binding

Question 19

does the C region of the heavy chain vary?

Answer 19

it does vary slightly between different classes of antibodies and this difference allows the classification of antibodies into 5 different classes., IgG, IgA, IgM, IgD, and IgE

Question 20

what does binding of the antigen-binding site of an antibody with antigen cause?

Answer 20

neutralisation
agglutination
precipitation

Question 21

what does the exposed Fc portion following antigen binding by the antibody promote?

Answer 21

complement fixation
opsonisation
activation of NK cells

Question 22

what is a complement?

Answer 22

A complex system of a number of serum proteins which act in a sequence

Question 23

what is the classical pathway of the antibody?

Answer 23

Antibody [IgM or IgG] binds to epitopes of antigen

Question 24

what does C1 bind to?

Answer 24

C1 binds to Fc region of antibodies

Question 25

what does C1r activate?

Answer 25

activates C1s which is a proteinase

Question 26

what does C1s do?

Answer 26

cleaves C4

Question 27

what does C4a and C4b bind to?

Answer 27

C4b antigen

C4a remains in fluid phase

Question 28

what does C1s do?

Answer 28

cleaves C2

Question 29

what does C2a and C2b do?

Answer 29

C2b binds to antigen; C2a remains in fluid phase

Question 30

what does C2b bind to?

Answer 30

antigen

Question 31

where does C2a remain?

Answer 31

in fluid phase

Question 32

what is C2b?

Answer 32

a proteinase which cleaves C3

Question 33

what do C3a and C3b do?

Answer 33

C3b binds to antigen; C3a remains in fluid phase

Question 34

what does C2b do?

Answer 34

cleaves C5