Virus-protection assay: Antiviral Assay (AVA)

Pharmaceutical proteins produced by using cell cultures and medical devices derived from animal tissues must be checked for virus contaminations according to USP Pharmacopoe Europeae or ISO standards. However, viruses used in these assays pose a risk of human infection. Therefore, these assays have to be performed under strict biosafety standards up to BL2 level.

Testing for antiviral activity can be performed at Fraunhofer IGB.  An Antiviral Assay (AVA) is routinely used for measuring the biological activity of interferons (IFN). The determination of the antiviral activity of interferons is based on the induction of cellular responses in cell cultures, suppressing the cytopathic effect of the infectious virus. This can be detected quantitatively using a simple and robust photometric assay. Additionally, other viral assays such as the Tissue Culture Infectious Dose50 (TCID50) and the Plaque Assay are carried out at our institute.

Process steps

Analysis of recombinant proteins for virus contamination.
Analysis of recombinant proteins for virus contamination.

Based on the extent of cytopathic effect (CPE) in the lung epithelial cell line A549, the sample activity was compared with the dose-response curve of the standard. A quantified virus titer was added to all assays. Cell controls received only cells and medium, while virus controls received virus but no test compound. Plates were incubated until the viral CPE in the virus control wells reached 100 % (mostly in 24 hours). The dilutions at which 50 % of the maximal cytopathic effect could be observed were compared and revealed the relative activity of the sample.The results were expressed as EC50 values defined as the concentration of compound achieving 50 % inhibition of the virus-reduced dye signals as compared with the uninfected cell control. The signal-to-noise ratio of an assay is the ratio between the mean dye signals of the cell controls and the virus controls. The dynamic range is defined as the ratio between the
signals at the last (maximal signal) and first point in the linear range of the dose-response curve.


  • Photometrical determination of the cytopathic effect of the respective virus


  • Testing of recombinant proteins for virus contaminations
  • Determination of the titer of cytopathogenic viruses in samples under contract for customers
  • Implementation of virus tests in the production process