Colony stimulating factor in human mixed leukocyte cultures.

Colony stimulating factor (CSF) is important for granulocyte/macrophage proliferation and differentiation. We investigated the relationship between the immune reactivity and the production of CSF by using two-way mixed leukocyte cultures (MLC) prepared from human peripheral mononuclear cells obtained with the aid of a blood cell separator. Assessed over 9 days of MLC incubation, the level of CSF in the supernatant reached a maximum at day 7 and then decreased. Optimal number of MLC cells ranged from 1 X 10(6)/ml to 2 X 10(6)/ml; CSF activity decreased at a cell concentration of 4 X 10(6)/ml. There was a differential sensitivity between cluster formation and colony formation to MLC-CSF. MLC-CSF is not species specific and hence, can stimulate both human and mouse CFU-c. MLC-conditioned medium (MLC-CM) appears to be a potentially useful source of CSF.