Page 1427 - Veterinary Immunology, 10th Edition

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FIG. 42.23 A radial immunodiffusion assay. The area of
precipitation is proportional to the concentration of antigen. In this
case, antiserum to bovine IgA is incorporated in the agar and is
used to measure bovine serum IgA levels.

Radial Immunodiffusion

If an antigen solution diffuses into agar in which specific antiserum
has been incorporated, a ring of precipitate will form around the
antigen well. The area of this ring is proportional to the amount of

antigen in the well. A standard curve may therefore be constructed
using known amounts of antigen (Fig. 42.23). Unknown solutions of
antigen can then be accurately assayed by comparing the ring

diameters from unknowns with the standard curve. This test is
used to measure serum immunoglobulin levels in newborn foals
(Chapter 23).

Immunoelectrophoresis and Related Techniques

Although conventional gel-diffusion techniques give a separate

precipitation line for each antigen-antibody system in a mixture, it
is often difficult to resolve all the components in a complex mixture.
One way to improve the resolution of the system is to first separate
the antigen mixture by electrophoresis before undertaking

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