WEEK 1 - antibodies Flashcards
B lymphocytes make…
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
what is a B lymphocyte
B lymphocytes each expressing a different B cell receptor, which is a membrane-tethered antibody
antibody isotopes
IgG
75% of circulating antibody and provides majority of antibody based immunity against pathogens
subtypes IgG1-4
shape: monomer (Y shape)
antibody isotopes
IgA
present in mucosal surfaces from bacteria
shape: dimer
antibody isotopes
IgM
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
antibody isotopes
IgD
on the surface of B cells
shape: monomer (Y shape)
antibody isotopes
IgE
bound to tissue cells
(e.g. mast cells) and associated with allergic reactions
only 0.002% of circulating antibody
shape: monomer (Y shape)
antibody modes of action
neutralisation
binding to toxins, viruses, or bacteria to prevent them acting in the body
antibody modes of action
opsonisation
coating of antigens (e.g. on dangerous pathogens) with antibodies, which can then be recognised by Fc receptors or complement receptors on phagocytic cells
antibody modes of action
complement action
Direct pathogen killing by pore forming complex; complement components can bind to antibodies as well as pathogens
antibodies neutralise toxins
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
antibodies neutralise viruses
virus action
1. virus binds to receptors on cell surface
- receptor mediated endocytosis of virus
- 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
antibodies neutralise bacteria
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
opsonisation with antibodies and complement enable…
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
what happens to cells that are too big to phagocytose
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)
what is the basis for some anti-cancer therapies
antibody-dependent cell-mediated cytotoxicity (ADCC)
antibody-antigen binding
due to complementary surfaces between antibody and antigen
antibody-antigen binding
interactions
non covalent interactions
- hydrogen bonds
- van der waals forces
- salt bridges
- hydrophobic interactions
monoclonal antibody generation using hybridoma technology
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
biotech companies and molecular biology techniques
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
blockbuster antibodies
Infiximab (remicade)
tumour nesrosis factor (TNF) to treat rhematoid arthritis, crohn’s disease and plaque psoriasis
blockbuster antibodies
adalimumab (Humira)
tumour nesrosis factor (TNF) to treat rhematoid arthritis, crohn’s disease and plaque psoriasis
blockbuster antibodies
Transtuzumab (Herceptin)
human epidermal growth factor receptor 2 (HER2) to treat cancer
MEMBRANE PROTEIN TARGET
blockbuster antibodies
Bevacizumab (Avastin)
vascular endothelial growth factor A (VEGFA) for cancer
