The antiproliferative activity of interferons assayed by measuring growth medium color changes related to cell number

A simple colorimetric assay for estimating cell numbers has been developed based on the observation that the indicator color in cell culture medium is proportional to viable cell number. The assay is performed in multiwell plates to take advantage of the rapid color measurement and computerized data handling capabilities of multiwell scanning spectrophotometers. Since no centrifugation or washing steps are involved, the technique is particularly useful for cells that grow in suspension, although it is equally applicable to monolayer cultures. The assay was developed to measure the antiproliferative activity of interferons on Daudi lymphoblastoid cells but could equally well be applied to other cell growth inhibition or stimulation assays.