Proliferation assay | Erika Wissinger, Imperial College London, UK
Objectives of the assay
The in vitro proliferation assay can be used to determine whether or not cells are triggered to divide after exposure to a specific stimulus, or to assess differences between cell populations in their ability to divide in response to the same stimulus.
1) Cells in culture are given a specific stimulus. For T cells, this is commonly plate-bound anti-CD3 antibody in combination with soluble anti-CD28 antibody (see figure). Other commonly used compounds to stimulate T-cell proliferation are Con A, PHA, and PMA and ionomycin.
2) A radio-labelled nucleotide is then addedto the culture media. The most commonly used is 3H-thymidine. As the cells are stimulated to divide, they utilise the radio-labelled nucleotide in the culture media and incorporate it into their newly-synthesized DNA. Each successive generation of daughter cells will incorporate more of the radio-labelled nucleotide into its DNA.
3) After this incubation (generally 24-48 hours), the cells are removed from the culture media by centrifugation and washed to remove any free radio-labelled nucleotide that has not been incorporated into the cells’ DNA. The total radioactivity is measured, and compared against a control group of cells that did not receive the proliferation-inducing stimulus.
Limitations and alternative approaches
The proliferation assay as described above provides information about the proliferation of a population of cells as a whole, rather than about individual cells. This assay is relatively quick and inexpensive to perform, but does involve the use of radioisotopes, and a specialized machine to read the level of radioactivity present in the samples.
An alternative experimental approach which provides more information about individual cells is to label cells in culture with a fluorescent marker, such as carboxyfluorescein succinamidyl ester (CFSE), which is diluted in each generation of daughter cells as they divide, and can be measured by flow cytometry.
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