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Radial immunodiffusion (RID)

A quantitative precipitation test in which an antigen diffuses outward through an agar gel containing specific antibodies, forming a visible ring.

Purpose of radial immunodiffusion

To measure the concentration of a specific antigen in a sample.

Location of antibodies in radial immunodiffusion

The antibodies are mixed throughout the agar gel.

Samples placed in wells during radial immunodiffusion

Samples containing the antigen being measured.

Antigen diffusion in radial immunodiffusion

It forms an antigen-antibody precipitate when it reaches the zone of equivalence.

Diameter of the precipitation ring in radial immunodiffusion

It indicates the concentration of antigen in the sample.

Use of a standard curve in radial immunodiffusion

Known antigen concentrations are used to create a relationship between ring diameter and antigen concentration, allowing unknown samples to be measured.

Effect of antigen concentration on precipitation ring

The diameter of the ring increases as antigen concentration increases.

Immunoelectrophoresis

A technique that combines electrophoresis and antibody precipitation to identify and analyze proteins in a complex mixture.

First major step in immunoelectrophoresis

Proteins in a sample are separated according to their electrophoretic properties.

Action after protein separation in immunoelectrophoresis

Antiserum is placed in a trough alongside the separated proteins.

Formation when antibodies meet proteins in immunoelectrophoresis

Visible precipitin arcs form.

Agglutination

The visible clumping of particulate antigens caused by antibody binding.

Difference between agglutination and precipitation

Agglutination involves particulate antigens, whereas precipitation involves soluble antigens.

Effective antibodies for agglutination

Antibodies with multiple antigen-binding sites, especially IgM, are highly effective at agglutination.

Direct agglutination test

A test in which antibodies directly cause visible clumping of cells or other particulate antigens.

Example of a direct agglutination test

Blood typing, in which antibodies cause red blood cells carrying specific antigens to clump.

Use of agglutination to identify bacteria

Antibodies specific to bacterial surface antigens can cause the bacteria to clump, indicating the presence of the target organism.

Passive agglutination

A test in which soluble antigens are attached to particles such as latex beads so antibodies can cause visible clumping.

Utility of latex beads in passive agglutination tests

They provide a visible particulate surface to which soluble antigens can be attached.

Reverse passive agglutination

A test in which antibodies are attached to particles, allowing them to detect soluble antigens by causing the particles to clump.

Basic difference between passive and reverse passive agglutination

In passive agglutination, antigen is attached to particles; in reverse passive agglutination, antibody is attached to particles.

Hemagglutination

Agglutination involving red blood cells.

Detection of viruses through hemagglutination

Some viruses have proteins that bind to receptors on red blood cells, causing the cells to agglutinate.

Hemagglutination inhibition test

A test that detects antibodies against a virus by determining whether those antibodies prevent the virus from agglutinating red blood cells.

Positive hemagglutination inhibition test indication

The patient's serum contains antibodies against the virus that block viral hemagglutination.

Complement fixation

A test that detects antibodies in a patient's serum based on whether antigen-antibody complexes activate and consume complement.

Indication of a positive complement-fixation test

Complement has been fixed by antigen-antibody complexes, indicating that antibodies against the tested antigen are present.

Usefulness of complement fixation for detecting antibodies

It can determine whether a patient's serum contains antibodies specific to an antigen of interest.

Overall purpose of antigen-antibody complex detection techniques

To detect, identify, or measure antigens and antibodies for diagnosis, research, and identification of microorganisms.