20 - antibodies

Question 1

what are antibodies?

Answer 1

immunoglobulins

large Y shape secreted glycoproteins

Question 2

structure of antibodies

Answer 2

• 2 identical heavy chains
• 2 identical light chains
• joined by non-covalent interactions and disulphide bridges
• N terminal variable region
• C terminal constant region
• can be secreted or membrane bound

Question 3

where does enzymatic cleavage of immunoglobulins (Ig) occur?

Answer 3

at the hinge region

Fab (fragment antigen binding) contains antigen-binding region

Fc (fragment crystallisable) interacts with Fc receptors on cells with C1q

Question 4

what is Fab?

Answer 4

fragment antigen binding

the arms of the antibody

Question 5

what is Fc?

Answer 5

fragment crystallisable

the bottom of the antibody

Question 6

main purposes of antibodies

Answer 6

bind specifically to epitopes on the pathogen/antigen that elect the immune response
• neutralisation and opsonisation

recruit cells and molecules to destroy the pathogen/antigen once the antibody is bound to it

Question 7

what region of the antibody is involved in effector functions?

Answer 7

the constant or C region (Fc)

Question 8

where does antigen binding occur?

Answer 8

macromolecules
• proteins
• carbohydrates
• nucleic acids

surfaces of intact protein molecules

other components on pathogen surfaces

Question 9

what is the epitope?

Answer 9

part of an antigen to which an antibody binds

antigenic determinant

Question 10

what are the 2 types of epitope?

Answer 10

linear - continuous

conformational - discontinuous

Question 11

what are antibody-antigen interactions made by?

Answer 11

non-covalent forces 
• van der Waals forces 
• hydrophobic interactions
• hydrogen bonds 
• electrostatic forces

Question 12

what is affinity?

Answer 12

strength of binding between a single antibody binding site and epitope

Question 13

why are multivalent antigens stronger?

Answer 13

more than 1 binding site employed

less likelihood of dissociation from both sites simultaneously

Question 14

what is avidity?

Answer 14

strength of binding between antibody and antigen
• affinity of an dauber of antigen binding sites
• greater than single site affinity
• many bacteria have multiple repeated epitopes

Question 15

6 functions of antibodies

Answer 15

• neutralisation
• opsonisation
• cell recruitment - ADCC
• agglutination
• cell recruitment - degranulation
• activate complement

Question 16

neutralisation

Answer 16

bind to bacteria/virus surface, bacterial toxin

prevent interaction with cell receptors

Question 17

opsonisation

Answer 17

direct - binding to receptors for antibody constant region (Fc receptors)

indirect - increasing complement deposition on pathogen and binding to complement receptors

Question 18

cell recruitment - ADCC

Answer 18

detection of antibodies by FcR on several cell types induces cell activation

Question 19

agglutination

Answer 19

cause bacteria/virus to clump together

Question 20

cell recruitment - degranulation

Answer 20

degranulation via Fc receptors (FcR)
• degranulation of mast cells
• killing by NK cells and eosinophils (ADCC)

Question 21

activate complement

Answer 21

classical pathway

antigen-antibody complex binds C1qrs

act on C4 and C2 to generate C3 convertase

Question 22

how can we use antibodies in the lab?

Answer 22

• enzyme linked immunosorbent assay (ELISA)
• flow cytometry
• immunoprecipitation
• fluorescence microscopy
• western blot