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Antigen antibody reactionVirus neutralization Virus Neutralization TestsHemagglutination inhibition testHemagglutination inhibition test is widely used to diagnose influenza, measles, mumps and other viral infections.e.g. If a person has measles, antibodies will be present in the serum to react with the measles viruses and neutralize them and there will be no agglutination of RBCs i.e. Hemagglutination inhibition. It will be a positive test for the viral infection being studied.

2. Inhibition of Cytopathic EffectsThe presence of antibodies against a virus can be detected by the antibodies ability to prevent cytopathic effects of viruses in cell cultures.

Virus + Serum Incubation add to tissue culture of the appropriate cells.

Serum with the Specific Ab No specific antibody

No CPE CPE

Immunofluorescence

Immunofluorescence (IF): is a microscopic technique that uses specific antibodies labeled with fluorochromes to detect, localize, or quantify microorganisms (or proteins expressed in virus-infected cells) in samples applied to slides.A variety of fluorochromes are available, but the most commonly used are fluorescein and rhodamine. These can be covalently attached to antibody molecules and made visible by UV light in the fluorescence microscope.

Two types Direct fluorescent Ab test: used to detect Ag or microorganismIndirect fluorescent Ab test: used to find a specific Ab in the serum

A. Direct fluorescent-antibody testIn the direct fluorescent-antibody test, the fluorescent dye is attached directly to the antibody that is interacting with the antigen (dark triangles) on the surface of the cell.

B. Indirect fluorescent-antibody testIn the indirect fluorescent-antibody test, the fluorescent dye is attached to antibody made against human IgG.