Production of colony stimulating activity in mixed mononuclear cell culture.

Culture medium was harvested after co-incubation of mononuclear cells collected and pooled from the peripheral blood of two different normal donors and was tested for colony-stimulating activity (CSA) in agar culture. With bone marrow from normal donors or peripheral blood from patients with chronic granulocytic leukaemia as sources of granulocyte-committed progenitor cells (CFU-c), such mixed mononuclear cell conditioned medium (MMC-CM) showed activity equal to that of unfractionated leucocyte feeder layers and greater than that of CSA prepared from lymphocytes stimulated by phytohaemagglutinin. The addition to plates of 2-mercaptoethanol during the preparation of MMC-CM enhanced CSA release. MMC-CM is thus a convenient source of CSA and its use may be preferable to that of feeder layers when day-to-day reproducibility is essential.