Neutralization is an antigen–antibody reaction in which the biological effects of viruses and toxins are neutralized by homologous antibodies known as neutralizing antibodies. These tests are broadly of two types: (a) virus neutralization tests and (b) toxin neutralization tests.
Neutralization of viruses by their specific antibodies are called virus neutralization tests. Inoculation of viruses in cell cul-tures, eggs, and animals results in the replication and growth of viruses. When virus-specific neutralizing antibodies are injected into these systems, replication and growth of viruses is inhibited. This forms the basis of virus neutralization test.
Viral hemagglutination inhibition test is an example of virusneutralization test frequently used in the diagnosis of viral infections, such as influenza, mumps, and measles. If patient’s serum contains antibodies against certain viruses that have the property of agglutinating the red blood cells, these antibodies react with the viruses and inhibit the agglutination of the red blood cells.
Toxin neutralization tests are based on the principle that bio-logical action of toxin is neutralized on reacting with specific neutralizing antibodies called antitoxins. Examples of neutral-ization tests include:
· In vivo—(a) Schick test to demonstrate immunity againstdiphtheria and (b) Clostridium welchii toxin neutralization test in guinea pig or mice.
· In vitro—(a) antistreptolysin O test and (b) Nagler reactionused for rapid detection of C. welchii.