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[link] summarizes the various types of antibody-antigen assays discussed in this section.
| Mechanisms of Select Antibody-Antigen Assays | ||
|---|---|---|
| Type of Assay | Mechanism | Examples |
| Precipitation | Antibody binds to soluble antigen, forming a visible precipitin | Precipitin ring test to visualize lattice formation in solution |
| Immunoelectrophoresis to examine distribution of antigens following electrophoresis | ||
| Ouchterlony assay to compare diverse antigens | ||
| Radial immunodiffusion assay to quantify antigens | ||
| Flocculation | Antibody binds to insoluble molecules in suspension, forming visible aggregates | VDRL test for syphilis |
| Neutralization | Antibody binds to virus, blocking viral entry into target cells and preventing formation of plaques | Plaque reduction assay for detecting presence of neutralizing antibodies in patient sera |
| Complement activation | Antibody binds to antigen, inducing complement activation and leaving no complement to lyse red blood cells | Complement fixation test for patient antibodies against hard-to-culture bacteria such as Chlamydia |
When slowly adding antigen to an antiserum, the amount of precipitin would gradually increase until reaching the ________; addition of more antigen after this point would actually decrease the amount of precipitin.
equivalence zone or zone of equivalence
The radial immunodiffusion test quantifies antigen by mixing ________ into a gel and then allowing antigen to diffuse out from a well cut in the gel.
antiserum
Explain why hemolysis in the complement fixation test is a negative test for infection.
What is meant by the term “neutralizing antibodies,” and how can we quantify this effect using the viral neutralization assay?
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