Immunodiffusion (ID) Assay
There are several types of immunodiffusion:
- Simple immunodiffusion (Oudin technique) in which one of the two reagents remains fixed (either the antigen or the antibody) and the other reagent moves
- Double immunodiffusion (Ouchterlony technique) in which antigen and antibody are free to move towards each other.
The immunodiffusion (ID) test, also called the Ouchterlony test, allows antigen detection. Immunodiffusion refers to the movement of the antigen or antibody or both antigen and antibody molecules in a diffusion support medium.
It is a method of gel immunodiffusion: the solutions deposited in the wells dug in the gel diffuse homogeneously in all directions around the well. Two diffusion rings may therefore come into contact when they have progressed sufficiently. This contact zone remains invisible if there is no reaction between the two solutions. When there is a reaction between the solutions, a precipitation arc is formed visible to the naked eye. This is due to the interaction between many antibodies and specific antigens, resulting in the formation of immune complexes. The reaction time is of the order of 24 hours.