XIII. PRECIPITATION REACTIONS

This results in a false-negative result

Prozone and Postzone

Maximum precipitation occurs when the concentrations of the antigen and antibody are about equal.

Zone of equivalence

• Occurs when excess amount of antibody is present, and the antigen and antibody do not combine to form precipitates—the complexes remain soluble.

Prozone

• Occurs when excess amount of antigen is present, and the antigen and antibody do not combine to form precipitates—the complexes remain soluble.

Postzone

the measurement of light transmitted through a suspension of particles.

Turbidimetry

• The formation of _____ decreases the amount of light passing through a suspension.

• The more formed it is and the larger they are, the greater is the decrease in light able to pass through.

• immune complexes

• A direct measure of light scattered by particles suspended in solution.

• The scattering of light is proportional to the size and amount of immune complexes formed.

Nephelometry 

______ is more sensitive than turbidimetry.

Nephelometry

• Is the precipitation of fine particles in a confined space.

• The serologic tests for syphilis, Venereal Disease Research Laboratory (VDRL) and rapid plasma regain (RPR)

Flocculation

Antigen and antibody diffuse through the agar gel and precipitate when they reach the zone of equivalence

Precipitation reactions in agar gel

• Antigen and antibody are placed in wells in the gel and diffuse toward each other.

• When optimum concentrations are met (at the zone of equivalence), a precipitate line forms.

• Precipitant lines between adjacent wells of antigen can be reported as identity, partial identity, or nonidentity.

Double immunodiffusion (Ouchterlony technique)

• Common errors in Double immunodiffusion (Ouchterlony technique) includes overfilling of wells, irregular well punching, unlevel incubation area, gel drying, increased room temperature, and antigen or antibody contamination by ____

bacteria or fungi.

• On an agar gel plate or slide, antigen is added to one well and antibody is added to another well.

• An electric current accelerates the movement of the antigen and antibody toward each other, resulting in precipitation sooner than if an electric current is not applied.

Countercurrent immunoelectrophoresis (CIE)

• CIE can be used to detect antibodies to ____ and ____.

• CIE has been replaced by easier-to-perform assays, such as ____.

• infectious agents ; microbial antigens

• agglutination tests

• Where serum, urine, or CSF is electrophoresed in a gel.

• Antiserum contained in a cellulose acetate strip is then placed on top of the electrophoresis gel.

• The antibodies diffuse into the electrophoresis gel and combine with the antigens, forming a precipitate.

Immunofixation electrophoresis

Immunofixation electrophoresis

• Detects the presence of an _____ in serum or urine

• immunoglobulin

• Used to quantify antigens

• Antigens are electrophoresed in agar-containing antibody.

• A pH is selected so that the antibodies are immobile.

Rocket immunoelectrophoresis