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A neutralizing antibody defends a cell from an antigen or infectious body by inhibiting or neutralizing any biological effect. The antibody response is crucial for preventing many viral infections and may also contribute to the resolution of an infection. When a vertebrate is infected with a virus, antibodies are produced against many epitopes of multiple virus proteins. A subset of these antibodies can block viral infection by a process called neutralization. This usually involves the formation of a virus-antibody complex.
Virus neutralization test
Neutralization of viruses by their specific antibodies are called virus neutralization tests. Inoculation of viruses in cell cultures, 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.
It is an example of virus neutralization 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.
This virus-antibody complex can prevent viral infections in many ways. It may interfere with virion binding to receptors, block uptake into cells, prevent uncoating of the genomes in endosomes, or cause aggregation of virus particles. Many enveloped viruses are lysed when antiviral antibodies and serum complement disrupt membranes. Antibodies can also neutralize viral infectivity by binding to cell surface receptors.
Toxin neutralization tests
Toxin neutralization tests are based on the principle that biological action of toxin is neutralized on reacting with specific neutralizing antibodies called antitoxins. Examples of neutralization tests include:
- In vivo: Schick test to demonstrate immunity against diphtheria and Clostridium welchii toxin neutralization test in guinea pig or mice.
- In vitro: antistreptolysin O test and Nagler reaction used for rapid detection of welchii.
Neutralizing antibodies have shown potential in the treatment of retroviral infections. Medical researchers have shown how the encoding of genes which influence the production of this particular type of antibody could help in the treatment of infections that attack the immune system. Experts in the field have used HIV treatment as an example of infections these antibodies can treat. Recently, potent and broadly neutralizing human antibodies against influenza have been reported, and have suggested possible strategies to generate an improved vaccine that would confer long-lasting immunity. Another disease which has been linked to the production of neutralizing antibodies is multiple sclerosis.
In diagnostic immunology and virology laboratories, the evaluation of neutralizing antibodies, which destroy the infectivity of viruses, can be measured by the neutralization method. In this procedure, patient serum is mixed with a suspension of infectious virus particles of the same type as those suspected of causing disease in the patient. A control suspension of virus is mixed with normal serum and is then inoculated into an appropriate cell culture. If the patient serum contains antibody to the virus, the antibody will bind to the virus particles and prevent them from invading the cells in culture, thereby neutralizing the infectivity of the virus. This technique is labor-intensive, demanding, and time consuming. It application is restricted to laboratories that perform routine viral cultures and related diagnosis.