PRECIPITATION REACTION

PRINCIPLE: When a soluble Ag combines with its Ab in the presence of electrolytes (NaCl) at a suitable temperature & pH, the Ag-Ab complex forms an insoluble precipitate.When instead of sedimenting, the precipitate remains suspended as floccules Flocculation reactionPrecipitation can take place in liquid media or in gels such as agar, agarose or polyacrylamide.

Applications of Precipitation reactionIt can be perform either a quantitative or qualitative test.Sensitive for the detection of Ags.Types of precipitation reactions:Ring testSlide testTube testImmunodiffusionElectroimmunodiffusion

3- IMMUNODIFFUSION (precipitation in gel) Advantages of immunodiffusion: Reaction is visible as a different band of precipitation. Stable, can be stained for preservation.

Indicates identity, cross reactions, non identity between different Ags.

II- Single radial immunodiffusion:

Principle: Antibody is incorporated into agar and antigen introduced into the well. As antigen diffuses into agar precipitation rings form depending on the concentration of the antigen.( Fig 3,4 ) .

Radial Immunodiffusion is used to measure IgG, IgM and complement components.

Single Radial Immunodiffusion. ( Fig 3)

Fig (4)