ANTIGEN ANTIBODY REACTION

By

Dr. Emad AbdElhameed Morad

Lecturer of Medical Microbiology and Immunology

It is a form of antigen antibody reactions in which the antigen is soluble.

Types: this reaction can be done in:

Precipitation

Tube Agar gel

o When solutions of the antigen and antibody are mixed in tubes, cloudiness or turbidity occur.

Precipitation in tube

o Example: Elek’s test.A strip of filter paper saturated with diphtheria

antitoxin is embedded in the agar plate.Diphtheria is inoculated at right angles to the filter

paper, then plates are incubated for two days at 37 degree.

If the organism is toxigenic, fine white lines of precipitation occur commencing from the streak.

Precipitation in agar

The serum of the patient (antibody) is added to a known antigen and then complement is added.

If the serum contains antibodies to this antigen, they unite together and fix the complement.

If the serum has no antibodies, the complement is left free in the solution.

The second step is addition of sheep red blood cells coated with their antibodies.

In negative sera, the complement is free so it will cause hemolysis of red cells.

In positive sera, the complement is fixed and no hemolysis occurs.

Complement fixation test

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