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Abstract
A rapid and sensitive method was developed for screening potential antiviral agents
against orthomyxo- and paramyxoviruses, using the MTT method with cell culture suspensions.
The cell lines used for the assay were as follows: MDCK cells for the influenza A
virus (Fluv. A), HeLa cells for the respiratory syncytial virus (RSV), and Vero cells
for the measles virus (MSV). Test compounds were diluted and plated in 96-well round-bottomed
microtiter plates. Trypsinized cell suspensions and viruses were added to each well,
the plates were then centrifuged (700 x g, 5 min, room temperature), and incubated
for several days. The MTT assay was carried out after the degeneration of virus-infected
cells became evident. The optical density (OD) of formazan was determined using a
computer-controlled microplate reader. With this assay system, the EC50 values of
Ribavirin (used as the reference compound) were 3.7 micrograms/ml for Fluv. A, 4.5
micrograms/ml for RSV, and 12.3 micrograms/ml for MSV, respectively. These EC50 values
were equivalent to those obtained using the plaque reduction assay. The confluent
cell culture system was inadequate for antiviral assays against RSV and MSV when the
MTT method was used, because the inhibition of formazan formation was not observed
in viral-infected cells. Moreover, the suspension method is more sensitive to the
cytotoxicity of antiviral agents than the confluent cell culture system.