Immunodiffusion

Immune diffusion test, an agar diffusion assay, represents a feasible in simple immunochemical method for the detection of antigen-antibody reactions,

Principle

An agar medium is used as the solid support, in which antigens and antibodies can spread by diffusion. Once suitable antibodies and antigen collide, they react to form a visible precipitate with the naked eye. This reaction, referred to as immunoprecipitation allowed a qualitative or quantitative analysis of the reactants.

Variants

In practice, single and double diffusion to be performed.

Simple diffusion

Here diffuses only one reactant. Two variants are applied:

• Oudin test, Oudin immunodiffusion, or linear Simple diffusion: In a test tube is poured, the antiserum containing antibodies in an agar gel. After solidification of the agar, it is overcoated with the antigen-containing solution. Provided that the antibody recognizes the antigen, and react with it to form one or more ring- precipitate ( s) ( ring test). The distance of the rings from the diffusion starting point, the surface of the agar gel may be measured. Using a calibration curve can make a statement about the concentration of the antigen. The test was introduced in 1946 by Jacques Oudin.
• Mancini test or single radial diffusion: The antiserum containing the antibody is on a solid support, usually a sheet of glass, cast in agar gel. After solidification of the agar are punched in the gel and filled in the antigen solution in the holes with a cork borer wells. The reaction with the antibodies results in the annular precipitates. By measuring the ring diameter, the antigen can be determined quantitatively.

Double diffusion

In the double diffusion diffuse both reactants. In addition, depending on the question several different antibodies or antigens can be used.

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

The test was conducted by Örjan Ouchterlony, who developed it, named.

Other methods

A combination of the double-diffusion technique, the immuno electrophoresis; they suitable for the analysis of complex systems.

In the modern laboratory, these techniques are now used rarely, as they were supplanted by improved immunochemical methods, in particular the immune assays.