immunochemical procedures require a suitable antiserum or monoclonal
antibody raised against the antigen of interest. Polyclonal antibodies are raised
by injectmg an immunogen into an animal and, after an appropnate time, col-
lecting the blood fraction containing the antibodies of interest. In producing
antibodies, several parameters must be considered with respect to the final use
to which the antibody will be put. These include (1) the specificity of the anti-
body, i.e., the ability to distinguish between different antigens; (2) the aVIdity
of the antibody, 1.e., the strength of binding; and (3) the titer of the antibody,
which determines the optimal dilution of the antibody in the assay system. A
highly specific antibody with high avidity may be suitable for immunohIs-
tochemistry, where it is essential that the antibody remains attached during the
extensive washing procedures, but may be less useful for Immunoaffinity chro-
matography, as It may prove impossible to elute the antigen from the column
without extensive denaturation.
To produce an antiserum, the antigen for the first immumzation is often pre-
pared in an adjuvant (usually a water-in-oil emulsion containing heat-kllled
bacteria), which allows it to be released slowly and to stimulate the animal's
Immune system. Subsequent mjections of antigen are done with incomplete
adjuvant that does not contain the bacteria. The species used to raise the anti-
bodies depends on animal facIlities, amount of antigen available, and the
amount of antiserum reqUlred. Another consideration IS the phylogenetic rela-
tionship between antigen and immunized speCIes. A highly conserved mam-
malian protein may reqUlre an avian species in order to raise an antibody.
Production of antibodies IS still not an exact SCIence and what may work for
one antigen may not work for another.