Neutralization test

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The neutralization test  (NT) is a variant of the plaque assay , with which neutralizing antibodies against certain viruses can be detected in the serum of a patient or a vaccinee . The binding of antibodies to the surface of the virus prevents it from being absorbed into the cell , so that it can no longer multiply and the number of plaques in a cell culture is reduced. The neutralization test is therefore also referred to as a plaque reduction assay .

Neutralizing antibodies are antibodies that can block the uptake of a virus into a cell. Only neutralizing antibodies are recorded in the neutralization test. Neutralizing antibodies that act against multiple strains of the virus are referred to as broadly neutralizing antibodies , e.g. B. Broadly neutralizing anti-HIV antibodies .

The NT can also for quantification of cell toxins (bacterial toxins ) are used, raised against the functional inhibitory antibodies.


The search for neutralizing antibodies against a particular virus is carried out as follows:

  • A known amount of virions is added to a cell culture. Cell destruction occurs due to the cytopathic effect of the virus.
  • In further approaches, the patient's serum or dilutions thereof are added to viruses and cell culture . If there are sufficient neutralizing antibodies against this virus in the serum, the cytopathic effect is reduced and the cells of the culture remain intact.
  • To determine the antibody titer , the patient's serum is diluted more and more in different cultures (1: 2, 1: 4, 1: 8, etc.). The last dilution in which more than 50% of the cell lawn is retained is called the titer.

Position in the medical routine

The neutralization test is a very complex and lengthy procedure, as devices are required for a cell culture and the test usually takes several days. Furthermore, in the case of pathogenic viruses, there are increased demands on the security level of the laboratory , since native viruses are used. Cell cultures also require a far greater amount of work and experience than the use of ready-made test kits.

However, the specificity of the NT reaction is not achieved by any automated immunassay , which is why the NT is often used as a reference test for quality control . There is no alternative to the neutralization test when looking for neutralizing antibodies.


  • H. Hof, R. Dörries: Medical Microbiology , 3rd Edition Stuttgart 2005 ISBN 3-13-125313-4 p. 42f.