Immunodiffusion test

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The immunodiffusion test , an agar diffusion test , is an immunochemical method for the detection of antigen - antibody reactions that can be carried out with simple means .

principle

An agar medium is used as a solid support in which antigens and antibodies can spread by diffusion . As soon as the antigen and the matching antibody meet, they react to form a precipitate that is visible to the naked eye . This reaction, known as immunoprecipitation, allows a qualitative or quantitative analysis of the reaction partners.

variants

In practice, single and double diffusions are carried out.

Single diffusion

Only one reactant diffuses here. Two variants are used:

  • Oudin test, oudin immunodiffusion, or linear single diffusion: the antiserum containing the antibodies is poured into an agar gel in a test tube . After the agar has solidified, it is covered with the solution containing the antigen. If the antibody recognizes the antigen and reacts with it, one or more circular precipitates are formed (ring test). The distance of the rings from the diffusion start point, the surface of the agar gel, can be measured. With the help of a calibration line, a statement can be made about the concentration of the antigen. The test was introduced in 1946 by Jacques Oudin .
  • Mancini test or radial single diffusion: The antiserum containing the antibodies is poured into an agar gel onto a solid support, usually a sheet of glass. After the agar has solidified, wells are punched in the gel with a cork drill and the antigen solution is poured into these holes. The reaction with the antibodies results in circular precipitates. The antigen can be quantified by measuring the diameter of the ring.

Double diffusion

With double diffusion , both reaction partners diffuse. In addition, several different antibodies or antigens can be used depending on the issue.

The Ouchterlony test allows the simultaneous, qualitative analysis of several antigen-antibody systems. A solid support, usually a glass plate or a Petri dish , is coated with agar gel. Antigens and antibodies are pipetted into pre-punched holes and diffuse towards each other. Annular precipitation lines form where antigen and antibody meet in an equivalent concentration. In this way one can make statements about identity, non-identity or partial identity of different antigens.

The test was named after Örjan Ouchterlony who developed it.

Other methods

A combination of the double diffusion technique with the electrophoresis , the immunoelectrophoresis . It is suitable for the analysis of complex systems.

These techniques are rarely used in modern laboratories today because they have been superseded by improved immunochemical methods, particularly immunassays .

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