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Assay Services

  • Plaque Assay
  • Plaque Inhibition Assay
  • TCID50 Assay
  • Hemagglutination Assay (HA)
  • Hemagglutination Inhibition Assay (HAI)
  • IC50 Assay
  • Microneutralization Assay
  • Fluorometric Neuraminidase Assay
  • SRID
  • Egg Infectious Dose (EID50)

Plaque Assay - Determines infectious virus particles in a sample. Virus is sequentially diluted and dilutions are plated on susceptible cells. Cultures are overlaid with nutrient agarose and plaques or pocks formed by cytopathic viruses can be quantitated. Click here for our protocol.

Plaque Inhibition Assay - This assay is requested frequently to test the efficacy of antiviral drug candidates. Drug is included in the agarose overlay and if effective will reduce the size and/or number of plaques observed.

TCID50 Assay - Quantitates infectious virus particles in a sample. Virus is sequentially diluted and dilutions are plated in replicate wells of susceptible cells. The TCID50 (50% Tissue Culture Infectious Dose) is that dilution of virus which will produce pathological change in fifty percent of cell cultures inoculated at a particular dilution. TCID50 values are normally very close to the Plaque Assay values for most cytopathic viruses. Click here for our protocol.

Hemagglutination Assay (HA) - Detects the presence of certain viruses that agglutinate red blood cells. This assay can be used to quantitate or type many virus strains. For example, influenza virus possesses the capacity to agglutinate red blood cells of specific animal species. It does this by cross linking sialic acid residues on the surface of red blood cells. In some labs, the hemagglutination assay is preferred for detecting influenza virus growth. The hemagglutination titer of an influenza virus sample can be determined when dilutions of virus are mixed with human or turkey red blood cells. The presence of virus will hold the red cells in a diffuse matrix and prevent them from settling out to the bottom of the well. Click here for our protocol.

Hemagglutination Inhibition Assay (HAI) - This test is based on the inhibition of viral agglutination by a specific antibody and can be used for virus identification or for assay of antibodies. This assay is still used as a standard for measuring the efficacy of influenza vaccines and potency of neutralizing antibodies.

IC50 Assay - The IC50 (50% Inhibitory Concentration) of an antiviral drug can be determined using tissue culture. A sample of known virus concentration is incubated with susceptible cells in the presence of increasing concentrations of an antiviral drug. This assay determines the concentration at which the drug will inhibit virus replication. This can also be done using antibodies in the place of drugs, in which case it is called a Microneutralization Assay.

Microneutralization Assay - An excellent test to determine if an antibody may have therapeutic effects. This assay measures the ability of an antiserum to inhibit cytopathogenic effect of about 100 virus infectious units. The antibody/virus mixture is plated on susceptible cells and inhibition is tracked.

Fluorometric Neuraminidase Assay - This assay measures a fluorogenic substance released by the active influenza neuraminidase enzyme. It is used to screen for antiviral drug activity against neuraminidase and determine the 50% Drug Inhibitory Dose.

SRID - The SRID Assay is used to quantitate the amount of antigen in a sample. Antigen concentration is determined by the degree of antigen/antibody precipitate around a well into which detergent solubilized virus is placed. A standardized antigen preparation and a specific polyclonal antibody are required.

EID50 - The 50% Egg Infectious Dose assay is carried out in the same manner as a TCID50 where every well is represented by a unique egg. Each virus dilution is injected into replicate eggs which are tested after a period of incubation for signs of virus growth. In the case of influenza we use the hemagglutination (HA) assay. We utilize other immunological tools for the detection of other viruses.

Call VIRAPUR at 858.824.9000 or email us at for more information.