Agglutination and precipitation can be used
for the detection of antibodies or antigens.
In the agglutination of antigen-coated particles,
there is detection of specific antibodies.
In nephelometry, there can be quantification of
proteins in serum, plasma or cerebrospinal fluid.
Immunoprecipitation can be used for the isolation
of specific antigen from a mixture of antigens.
And radial immunodiffusion used for
the quantification of antigens.
In agglutination assays, particles are
coated with either antibody or antigen.
In this case, the particle is being
coated with the IgG antibody.
You now have a particle
that is sensitized with IgG.
A rheumatoid factor negative serum will not
cause agglutination of these particles.
However if a patient has rheumatoid factor which
are autoantibodies directed to the Fc part of IgG,
then addition of serum from that rheumatoid
factor positive patient will cause agglutination.
In nephelometry, the presence of an
analyte in a test sample can be detected.
Specific polyclonal antibodies are mixed with
the sample containing the suspected analyte.
These are added to a cuvette and
immune complexes will form if there
is the analyte for that particular
antibody present in the test sample.
Laser light is then shone onto the
cuvette and there will be light
scatter depending upon the amount of
immunoprecipitate that is formed.
The light scatter is
detected using a photodiode.
The light scatter is proportional to the number of immune
complexes, in other words the concentration of the analyte.
In immunoprecipitation, there is a mixture of antigens
with the antigen of interest but also other antigens.
A excess of immobilized antibody specific
for the antigen of interest is added.
This causes precipitation when the antigen of interest is bound
by the antibody, immobilized onto for example a particle.
And these immobilized antibodies
bound to the antigen of interest can
then be deposited at the bottom of
a test tube using centrifugation.
These can then be washed with a fresh
solution to remove any unbound antigen.
And then the antibody denatured to
release or elute the antigen of interest,
thereby isolating that specific
antigen from a mixture of antigens.
In radial immunodiffusion, there is an agarose
gel containing specific polyclonal antibody.
Wells are cut into the gel and the
test sample added to one of the wells.
There are also standards with defined
concentrations of the antigen added to the gel.
After 24-48 hours, precipitant
rings will be produced.
As the analyte diffuses into the gel, specific
antibody binds and the precipitate forms.
The size of the precipitation ring depends
on the quantity of analyte loaded.