immunoassays Flashcards
give some examples of immunoassays?
pregnancy tests
lateral flows
why is the use of antibodies in research, diagnostics and treatment widespread?
because of their ability to specifically bind to antigens and their ability to fix complement
how are antibodies produced?
theyre produced through matured b cells and are then clonally expanded and with the help of t cells, the b cells become plasma and start to secrete antibodies
how specific do you want antbodies to be for the purpose of recognising analyte if it has high avidity?
you want them to be really specific
what does analyte mean?
a substance whose chemical constituents are being identified and measured.
what tells the b cells what isotype of antibodies to make?
the signals around them
what does it mean if an antibody is specific and has high avidity?
this means that theyve got a high ability to bind
what does multiple immunisations increase?
it increases the amount and affinity of the antibody in the serum of immunised animals
what is the first isotype of antibody produced?
IgM
how do IgG antibodies get produced after immunisations?
the first type of antibodies produced are IgM then they undergo class switching to IgG which is highly specific and is produced after immunisations
if your making antibodies for use in humans, are they produced in humans first?
no, as they’ll target the own body, you make them in another animal
what is the process for producing antibodies for use?
o Once the amimals have been immunologically primed (mounted an antibody repsinse), they have high levels of specific antibody in the serum
o This means they can therefore collect the blood, separate serum and use this antiserum for future tests, treatments ect
o You can repeatedly bleed antimals, allowing a plentiful source of antiserum
You can collect several liters of antiserum from an immunised cow each month
o this is releatively cheap and easy and allows for the generation of polyconal antibosies
what is the problem with using serum as a way of making antibodies ?
it contains many other proteins which may cause problems to sensitive assays
why is it better to purify antibodies?
for improved storage and higher concentraion
it also allows you to only have helpful antibodies
what are the steps of the purification of antibodies from antiserum?
- the b cell binds the virus through the viral coat of the protein
- then the virus particle is internalised and degraded
- the peptides from internal proteins of the virus are presented to the t cell, which activates the B cell
- activated B cell produces antibody against viral coat protein
what does multiple immunisations do for the amount and affinity of antibodies in the serum of immunised animals?
it increases both the amount and affinity of antibodies in the serum of immunised animals
what does multiple immunisations also result in? [in terms of the type of antibody]
it results in class switching with the antibodies more likely to be IgG or IgA
what do you need to consider when generating antibodies for use?
antigen- so you make an antibody actually specific to the antigen
adjuvant - you want one thats effective at enhancing the body’s immune response to the antigen
kenetics- dunno why, just know theyre important
what does it mean when animals are immunologically ‘primed’?
they mount an antibody response
how do you get antiserum?
you immunise an animal until it gets an antibody response then collect the blood, separate the serum (antiserum)
what can antiserum be used for?
future tests
treatments
what is a relatively cheap way of producing polycolonal antibodies? and why?
antiserum
as you can repeatedly bleed animals allowing for plentiful source of antiserum and you can collect several litres of antiserum of an immunised cow every month
what are the cons of generating antibodies through serum?
the serum contains many other proteins which may cause problems in sensitive assays e.g. cross reactivity
therefore its better to purify improved storage and higher concentration
how do you purify antibodies for use?
the animal is immunised, then the serum is extracted which includes antibodies then the antibodies are bound to a protein and the serum proteins are washed off and elute the bound antibodies
what are the problems with polyclonal antibodies?
- theres lots of different classes and isotopes of antibodies present
- theres potentially different specificities against different parts of the molecule
- potentially contaminating antibodies that react with other proteins
- Sometimes need reagents that are much more specific & well characterised (e.g. for injecting into patients!)
how do you make monoclonal antibodies?
to make hybridomas, to fuse an antibody-forming cell with a tumour cell, then the antibody producing hybridomas are cloned and screened for antibody production, then monoclonal antibodies are isolated for cultivation
what are monoclonal antibodies used for?
they can be ised for many things such as experiments or tests for covid
what are the advantages of monoclonal antibodies?
- they can be produced in large quantities without the need for repeated bleeding of animals
- bind very specific epitope of an antigen
- exactly the same immunoglobulin class and isotype
- they can be highly purified
- allows for in depth analysis without batch variation to quantify specific analytes and to treat patients
what are the steps of using a bacteriophage to screen and produce monoclonal antibodies?
- isolate population of genes encoding antibody variable regions
- construct fusion protein of V region with a bacteriophage coat protein
- cloning a random population of variable regions gives rise to a mixture of bacteriophage - a phage-display region
- select phage with desired V regions by specific binding to antigen
what are the positives to phage display production of monoclonal antibodies?
- allows for rapid screening of many more V region expressing clones against the antigen of interest, increasing sensitivity and the likelyhood of success
- other subsequently use genes from positve clones and express into hybridoma (allows production of mammalian/ humanised monoclonal antibodies)
what negative is there to phage display production of monoclonal antibodies?
some versions of this method allow for the production of monoclonal antibodies by bacteria (meaning you get lots of proteins, cheap but not nessisarily corrcect folding)
theres also issues with morals as youre using antibodies from animals
how are nanobodies made?
theyre made through phage display but by using libraries from immunised camelids
what is the difference between convntional antibodes and nanobodies?
the conventional antibodies have heavy and light chains whereas the nanobody, also referred to as single domain-based VHHs, are antibody fragments derived from heavy-chain only IgG antibodies found in the Camelidae family
what are the advantages to nanobodies?
Produced recombinantly: known sequence,
little batch-to-batch variation
Small size: better tissue, good for imaging and therapeutic antibodies
No heavy or light chains: less likely to generate an immune response
High stability: as smaller proteins
what are some applications for antibodies?
medical diagnostics, treatment of immune deficiencies and some types of cancer, and prenatal therapy specifically to minimize the risk of hemolytic disease of the newborn
why would antibodies be conjugated to an enzyme or flurochrome?
to allow for the detection of antibody
what types of things can be conjugated with antibodies to help them be read out?
enzymes
radiation
fluorescence
what are enzymes used for when theyre conjugated to antibodies?
they can be used to catalyse a reaction, often resulting in a colour change
what does radiation do when its conjugated to an antibody?
can link/ incorperate radioactivity emitters with the antibody
subsequently detect the radiation (alpha, beta or gamma) as appropriate
what does fuorecence do when conjugated to antibodies?
its an increasingly popular method as it avoids hazards associated with radiation but it can require expensive equipment to detect
what things can antibodies be linked chemically to which act as reporter molecules?
enzymes
fluorecence
radioactive molecules
enzyme beads
what is serology?
its the method used to detect or quantify antibodies in response to microbial infections
what can serology be used for?
it can determine if a person has experienced an infection as theyre produced during infections
it can also determine the strain of microbe the person has been infected with
the type of antibody that has been detected can also say if the infection is recent or historic and about the type of cellular immune response that was produced
what type of infection is IgM associated with?
a recently aquired infection
what type of infection is IgG associated with?
its associated with a historic or chronic infection
what can knowing the type of antibody present be useful for?
its useful in situations where the treatment, disease prognosis or other risks are affected by this consideration - pregnant people preventing the vertical spread of infections such as toxoplasmosa gondii
what are the steps of an ELISA for IgG?
- coat the surface with antigen
- add serum (this contains the IgG)
- add anti-IgG
- ass substrate
- stop the reaction and measure the level of antibody by measuring the absorbance
what is the difference between the ELISA for IgG and for IgM?
the only difference is the serum added and the anti-IgG is substituted for anti-IgM