WEEK 1 - antibodies

Question 1

B lymphocytes make…

Answer 1

antibodies
via clonal selection and proliferation

Antibodies are a soluble form of the b cell receptor
- Need to be soluble to travel to target cells

Question 2

what is a B lymphocyte

Answer 2

B lymphocytes each expressing a different B cell receptor, which is a membrane-tethered antibody

Question 3

antibody isotopes
IgG

Answer 3

75% of circulating antibody and provides majority of antibody based immunity against pathogens

subtypes IgG1-4

shape: monomer (Y shape)

Question 4

antibody isotopes
IgA

Answer 4

present in mucosal surfaces from bacteria

shape: dimer

Question 5

antibody isotopes
IgM

Answer 5

on the surface of B cells and 10% of circulating antibody

shape: pentamer
5 Ys together
10 binding regions
Slightly lower affinity for each binding site but has 10

Question 6

antibody isotopes
IgD

Answer 6

on the surface of B cells

shape: monomer (Y shape)

Question 7

antibody isotopes
IgE

Answer 7

bound to tissue cells
(e.g. mast cells) and associated with allergic reactions

only 0.002% of circulating antibody

shape: monomer (Y shape)

Question 8

antibody modes of action
neutralisation

Answer 8

binding to toxins, viruses, or bacteria to prevent them acting in the body

Question 9

antibody modes of action
opsonisation

Answer 9

coating of antigens (e.g. on dangerous pathogens) with antibodies, which can then be recognised by Fc receptors or complement receptors on phagocytic cells

Question 10

antibody modes of action
complement action

Answer 10

Direct pathogen killing by pore forming complex; complement components can bind to antibodies as well as pathogens

Question 11

antibodies neutralise toxins

Answer 11

preventing from binding to receptor and effecting cell

toxin action
1. toxin binds to cellular receptor
2. endocytosis of toxin receptor complexes
3. dissociation of toxin to release active chain which poisons cell

antibody protects cell by blocking binding of toxin

Question 12

antibodies neutralise viruses

Answer 12

virus action
1. virus binds to receptors on cell surface

2. receptor mediated endocytosis of virus
3. acidification of endosome after endocytosis triggers fusion of virus with cell and entry of viral DNA

antibody blocks binding to virus receptor and can also block fusion effect

Question 13

antibodies neutralise bacteria

Answer 13

action of bacteria
1. colonization of cell surface by bacteria which bind to surface via bacterial adhesins
2. some bacteria become internalised and propgate in internal vesicles

antibodies against adhesins block colonisation and uptake, so bacteria cannot get into bacteria

Question 14

opsonisation with antibodies and complement enable…

Answer 14

toxin and pathogen clearance

Fc region of antibodies bind to Fc receptors on macrophages to enable phagocytosis

complement complex kills bacteria directly by forming pores

Question 15

what happens to cells that are too big to phagocytose

Answer 15

Natural killer (NK) cells kills them

antibody binds to antigen on the surface of target cells

Fc receptors on NK cells recognise bound antibody

cross linking of Fc rceptors siginals the NK cell to kill the target cell

target cells dies by apoptosis

this is termed antibody-dependent cell-mediated cytotoxicity (ADCC)

Question 16

what is the basis for some anti-cancer therapies

Answer 16

antibody-dependent cell-mediated cytotoxicity (ADCC)

Question 17

antibody-antigen binding

Answer 17

due to complementary surfaces between antibody and antigen

Question 18

antibody-antigen binding
interactions

Answer 18

non covalent interactions
- hydrogen bonds
- van der waals forces
- salt bridges
- hydrophobic interactions

Question 19

monoclonal antibody generation using hybridoma technology

Answer 19

classical way of producing antibodies

spleen cells producing antibody from mouse immunized with antigen A and Myeloma cells (immortal) lacking antibody secretion and the enzyme HGPRT [used to make cells immortal]

mix and fuse cells with PEG

transfer to HAT medium
- immortal hybridomas proliferate; mortal spleen cells and unfused HGPRT myeloma cells die

select hybridoma that makes antibody specific for antigen A

clone selected hybridoma

HAT blocks DNA synthesis
HGPRT can bypass this block

Question 20

biotech companies and molecular biology techniques

Answer 20

companies obtain the cDNA sequence of newly developed antibodies and humanise them using molecular biology techniques

Want to be as close to human as possible
Other antibody will be destoryed by body’s own immune system
- As it will be recognised as a forgein cell

Question 21

blockbuster antibodies
Infiximab (remicade)

Answer 21

tumour nesrosis factor (TNF) to treat rhematoid arthritis, crohn’s disease and plaque psoriasis

Question 22

blockbuster antibodies
adalimumab (Humira)

Answer 22

tumour nesrosis factor (TNF) to treat rhematoid arthritis, crohn’s disease and plaque psoriasis

Question 23

blockbuster antibodies
Transtuzumab (Herceptin)

Answer 23

human epidermal growth factor receptor 2 (HER2) to treat cancer

MEMBRANE PROTEIN TARGET

Question 24

blockbuster antibodies
Bevacizumab (Avastin)

Answer 24

vascular endothelial growth factor A (VEGFA) for cancer

Question 25

blockbuster antibodies
Rituximab (Rituxan)

Answer 25

CD20 to treat rheumatoid arthiritis and non-Hodgkin lymphoma

MEMBRANE PROTEIN TARGET

Question 26

Rituxan (and Herceptin)
how it works

Answer 26

works by depleting tumour cells

1) antibody-dependent cellular cytotoxicity
- CD20 very highly expressed on certain b cancer cells

2) complement-dependent cytotoxicity

Question 27

mechanisms of therapeutic antibody action

Answer 27

blocking

signalling

targeting

ADCC - antibody-dependent cell-mediated cytotoxicity

CDC - complement-dependent cytotoxicity

Question 28

strengths of therapeutic antibodies

Answer 28

established methods for antibody generation and optimisation

growing repertoire of technologies to redesign antibodies with modified or new properties to enhance their clinical potential

high success rate compared to other drugs

established production technologies

often well tolerated by patients

fastest growing class of therapeutics

Question 29

limitations of therapeutic antibodies

Answer 29

expensive due to high production costs and commonly large doses, potentially limiting patient access or clinical applications

clinical applications currently limited to cell surface or extracellular targets

cannot be orally administered (it would just be digested in the stomach have to be injected)

large size of IgG may limit tissue penetration

limited penetration of the central nervous system due to inefficient penetration of the blood-brain barrier