Precipitation Reactions

Principle

• in a solution or matrix, soluble antigen and antibody combine in proportion at or near equivalence

Prozone Effect

• antibody excess

Postzone Effect

• antigen excess

Prozone

• antigen combines with only one Ab and no cross linkages form

Post Zone

• every available Ab binding site is bound to a single antigen

Zone of Equivalence

• number of multivalent sites of antigen and antibody are approximately equal

• this zone antibody and antigen can bind together more optimally

Qualitative Precipitation Tests

• simple immunodiffusion (Ouchterlony) 

• Precipitin Patterns 

NonIdentity 

• precipitin lines cross one another 

• unrelated antigens and no common epitopes 

Identity 

• lines fuse and form an arch 

• identical antigens and presence of a common epitope

Partial Identity

• two precipitin lines fuse and form a spur to one side 

• antigens share an epitope but one antigen contains additional epitopes

Quantitative Precipitin Tests

• single radial immunodiffusion 

• immunoelectrophoresis

Single Radial Immunodiffusion

• Ab plated on solid medium and diffuses

• the larger the radius= the greater the antigen concentration 

Immunoelectrophoresis

• electrophoresis separates proteins

• Ab is added then diffused 

• precipitin lines form where Ab-Ag combination occurs 

Immunofixation electrophoresis

• Ab is added to gel surface 

• lanes will show heavy and light chains 

• will sho hypo and hyper aggammaglobulinemia 

Turbidimetry

• measurement of light transmitted through a suspension of particles

Nephelometry

• direct measurement of light scattered by particles suspended in solution 

Flocculation 

• soluble antigen/antibody form precipitate of very fine particles

• reserved for syphilis testing 

Sensitivity

• ability to correctly identify patients WITH the disease

Specificity

• ability to correctly identify patients without the disease