Immunological Test

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Antigen-Antibody interactions

Characterized as:
Non-covalent interaction (similar to “lock and key” fit of enzyme-substrate)
Does not lead to irreversible alteration of Ag or Ab
This exact and specific interaction has led to many immunological assays used to:
detect Ag or Ab
diagnose disease
measure magnitude of humoral IR
identify molecules of biological and medical interest


Precipitation Rxns:
Ab’s and Ag’s in aqueous soln’s form a lattice => Precipitin
Lattice formation requires
1) polyvalent Ab’s
2) Ag must be bivalent, polyvalent

Precipitation reactions depend on the formation of lattices and occur best when antigen and antibody are present in optimal proportions. Excess of either component decrease lattice formation and subsequent precipitation.


. Immunodiffusion procedures: are precipitation reactions carried out in an agar gel medium. Antibody and antigen are loaded in different wells and diffuse through the medium. When the optimal antigen-antibody ratio is reached a visible band appears in the gel.


Immunoelectrophoresis: Involves electrophoresis with double diffusion.
Immunoelectrophoresis combines electrophoresis with immunodiffusion for the analysis of serum proteins.
An Ag mixture is 1st separated by charge
Then, “troughs” are cut ∥ to direction of electric field and antisera is added to trough.
Ag’s and Ab’s diffuse towards each other to produce precipitin bands