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Index >>Immunity >> Gel Diffusion

Gel Diffusion

	Gel Diffusion Gel diffusion precipitation utilizes agar or other gels in either tubes or petriplates. The factors that govern precipitation in liquid solutions are also involved in gel systems. Both antigen and antibody diffuse freely through gels in all directions. At a certain point, depending on the rate of diffusion and the concentration of the reactants, a zone of equivalence will be formed, at which place visible precipitation will occur. If antigen or antibody preparations are complex, multiple bands of precipitate will form because of the variable diffusion rates of the components.
A useful technique of this is the Ouchterlony double diffusion method. Antigen and antibody preparations are placed in separate wells cut in a thin layer of agar in petriplates. The reactants diffuse out through the agar until they meet at optimal proportions and form bands of precipitate. In reactions of identity, where the two antigens are identical, the two precipitin bands merge to form a solid chevron between the two antigen wells and the antibody well. In reactions of non-identity, where the two antigens are unrelated, the precipitin line produced with one antigen completely crosses that produced by the other.
This obviously implies that the antiserum contains two specific antibodies, one specific for antigen A and the other specific for antigen B. In reactions of partial identity, a different pattern is seen. The antigenic preparations AB and AC have a common antigen A. The antiserum has antibodies AB, and therefore primarily reacts with antigenic preparation AB, but partially with antigenic preparation AC. The result is a spur of precipitation with antigenic preparation AB. There are numerous variations of the gel diffusion methods, such as the linear single immunodiffusion technique of Oudin, the linear double immunodiffusion technique of Okley and Fulthorpe and the radial immunodiffusion technique .

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