Practical in vitro assay systems for the measurement of hematopoietic growth factors

Summary A tetrazolium salt (MTT) was used to develop rapid, practical colorimetric assays for the measurement and differential identification of picomolar levels of certain hematopoietic growth factors (GM-CSF, CSF-1, and Multi-CSF/IL-3). The signal generated is directly proportional to the number of viable target cells present after 2 d of culture. Thus, this method can be used to quantitate proliferation or survival of all types of factor responsive cells in vitro. Assays using MTT reduction or [³H]thymidine as read-outs give comparable results; however, MTT reduction is easier, faster, and less expensive. The use of two target cell lines, each with well-characterized growth factor responses, and with differing responsiveness to the myeloid growth factors CSF-1, GM-CSF, and Multi-CSF/IL-3, is described. We further detail steps necessary to adapt other target cells to this convenient assay system.