1. Precipitation
Aggregation of soluble antigens with antibody to form visible complex
Directly visualize reactions

2. Precipitation
Nephelometry
Measures the light that is scattered at a particular angle from the incident beam as it passes through a suspension
The amount of light scatter is related to the concentration of precipitated particles (i.e., Ag/Ab complexes)
Quantitative method

3. Precipitation
Nephelometry

4. Double Immunodiffusion (Ouchterlony)
Precipitation
Double Immunodiffusion (Ouchterlony)
Antibody and antigen diffuse
Visible precipitate will form if:
Ab recognizes and has an affinity for antigen
Ag/Ab concentration within equivalence zone
All other physical conditions conducive for Ag/Ab reaction (i.e., pH, temp, etc.)
Rxn may take hours to days

5. Double Immunodiffusion (Ouchterlony)
Precipitation
Double Immunodiffusion (Ouchterlony)
Line of identity
Patient’s serum has an antibody to antigen A
The antibody is identical to the known antibody to antigen A

6. Double Immunodiffusion (Ouchterlony)
Precipitation
Double Immunodiffusion (Ouchterlony)
Line of partial-identity
Patient’s serum contains an antigen that reacts with anti-Aa
Patient’s antigen similar but not identical to the known antigen

7. Double Immunodiffusion (Ouchterlony)
Precipitation
Double Immunodiffusion (Ouchterlony)
Line of non-identity
Patient’s serum contains an antibody to the antigen AB
Patient’s antibody different than the known antibody

8. Double Immunodiffusion (Ouchterlony)
Precipitation
Double Immunodiffusion (Ouchterlony)
No reaction
Patient’s specimen doesn’t contain Antigen A or
Antigen and antibody concentration not within equivalence zone

9. Immunofixation Electrophoresis
Precipitation
Immunofixation Electrophoresis
Proteins separated by electrophoresis
Cellulose acetate strips impregnated with antibody applied to the gel
Diffusion
Precipitated complexes form

10. Immunofixation Electrophoresis
Precipitation
Immunofixation Electrophoresis
Useful in demonstrating antigens in low concentrations
Urine & CSF
Semi-quantitative

11. Western Blot Analysis Some references consider
a type of precipitation rxn (IFE)
“conceptually similar” to a precipitation rxn
Proteins (i.e., antigens of virus) separated in gel via electrophoresis
Separated proteins transferred or “blotted” onto nitrocellulose paper
Incubate with serum to detect antibodies to separated proteins

12. Western Blot Analysis

13. Flocculation
Soluble antigen and antibody form precipitate of fine particles
Visible (microscopically or macroscopically) because lattice is forced to remain in a confined space
Syphilis testing (RPR & VDRL)