activation are key areas in a wide variety of cell biological
approaches. The need for sensitive, quantitative, reliable and automated methods
led to the development of standard assays. Such an example is based on the
capability of the cells to incorporate a radioactively labeled substance ([3H])-
thymidine), or to release a radioisotope such as [51Cr] after cell lysis.
Alternatively, the incorporation of 5-bromo-2’-deoxyuridine (BrdU)* in place of
thymidine is monitored as a parameter for DNA synthesis and cellular
proliferation in immunohisto- and cytochemistry, in a cell ELISA and FACS
analysis. (kits and reagents for these applications are available from Roche
Molecular Biochemicals). Cell proliferation and viability assays are of
particular importance for routine applications. Tetrazolium salts (e.g. MTT,
XTT, WST-1) are especially useful for assaying the quantification of viable
cells, because they are cleaved to form. a formazan dye (fig. 1; for UV
absorbance spectrum, see fig. 2) only by metabolic active cells.
