Before we begin a discussion of this work we need some basic information about
antibodies and antigens. Antigens are anything that the
body recognizes as foreign. These can be chemical compounds, proteins,
and particulate matter (dust, pollen, etc.). Antibodies are protein
molecules that are produced by the body and are highly specific for
each antigen. The antibodies bind with the antigen to effectively remove
the foreign substance from the body. This is the body's
normal immunological response to a potential foreign substance that
might do harm. Sometimes there are no obvious symptoms of these interactions;
however, in other cases the symptoms are more bothersome as in the case
of those who suffer from allergies. The reactions sparked in the human
body can be mild, such as in hay fever, or very deadly, such as those
caused by bee stings or for those with serious food allergies.
The resulting highly specific antibody can be used as the basis of
an assay procedure for the antigen. Using this property, scientists
have devised a number of highly useful tests that have become common.
By binding a marker, such as an enzyme (a protein that catalyzes a biochemical
reaction), to the antibody, they could then analyze for enzymatic activity
and thereby obtain a measure of how much antigen might be present or
absent in the solution. A number of enzymes have been used in these
methods, but the most common are enzymes that can cause a specific substrate
to change color. Since the antibody and enzyme are linked, they
can be used to determine how much of the antigen is present in the solution.
Such tests are called an "enzyme-linked immunosorbent assay"
or ELISA for short. Typically, home pregnancy kits are based on these
types of assays.
The enzyme linked antibody can be in solution or can also be attached
to a solid material. Currently, the most common form of these assays
consists of an antibody attached to a solid surface. For example, if
an antibody for a toxin such as domoic acid were prepared and then linked
to an enzyme, we would have the basis for a sensitive, specific test
for domoic acid. In such a test, if a solution containing domoic acid
were then added to this linked antibody-enzyme complex, the domoic acid
would bind to its specific antibody. Then by analyzing
for the activity of the enzyme, we would know how much domoic acid was present in the sample.
In all of this, they key ingredient to the success of an ELISA is the
antibody. The production of the antibody to a specific antigen is sometimes
very difficult. In most all cases it calls for the challenging
a host animal (sheep and rabbits are most commonly used) with small
sub-lethal doses of antigen (for example domoic acid or PSP toxins)
then harvesting blood serum. The antibodies produced in these challenges
are then recovered from the serum by a series of extractions and purifications.
Getting an antibody response from small molecules, such a domoic acid
or the PSP toxins, is even more difficult and many times the yield of
antibody (the titer) is quite low. Various techniques are sometimes
used to increase this yield that might work in some cases but not in