Antigen-Antibody Interaction, Precipitation, Agglutination Part 3

What is agglutination?

Visible aggregation of particles caused by combination with a specific antibody.

Where does the agglutination reaction take place?

On the surface of an insoluble particle.

What are examples of particles involved in agglutination?

• RBCs

• Bacterial cells

• Latex particles.

What are the two steps of agglutination?

Sensitization and lattice formation.

What is sensitization?

The initial binding of antigen and antibody; it is not visible by eye.

What is lattice formation?

Cross-linking of antibodies that bridge the gap between particles and form visible aggregates.

What is direct agglutination?

Agglutination where the antigen is naturally found on the particle.

What is hemagglutination?

Agglutination involving RBCs.

What is an example of hemagglutination?

ABO typing.

How is ABO typing performed using direct agglutination?

Patient RBCs are mixed with reagent antisera.

How can patient antibodies be tested using RBCs?

Patient serum is mixed with reagent RBCs.

What is passive (indirect) agglutination?

Agglutination where a particle is coated with an antigen that is not naturally found on the particle.

What are examples of particles used in passive agglutination?

• RBCs

• Siliates

• Gelatin

• Latex particles.

Why are latex particles useful in passive agglutination?

They are inexpensive

What is reverse passive agglutination?

Agglutination where the particle is coated with antibody.

What type of antibody is preferred for reverse passive agglutination?

Monoclonal antibody.

How are antibodies positioned on particles in reverse passive agglutination?

The Fab sites face outward.

What is agglutination inhibition?

A test where the particle and antibody compete for binding sites on an antigen.

What does a lack of agglutination mean in agglutination inhibition?

A positive result.

How does agglutination inhibition work when patient antigen is present?

Patient antigen binds and blocks the known antibody

What happens when patient antigen is present and indicator particles are added?

No agglutination is observed because the antibodies are blocked.

What happens when there is no antigen in the patient's sample?

The known antibodies remain unblocked and can bind the indicator particles.

What happens when there is no patient antigen in agglutination inhibition?

Agglutination is observed.

Why does agglutination occur when there is no patient antigen?

The antibodies are not blocked and can bind the indicator particles.