Induction of colony-stimulating factor from quiescent fibroblasts by avian macrophages and monocytic leukemic cells

Confluent, quiescent chick embryo fibroblasts maintained in protein-free medium released CSF(s) active on granulocyte and monocyte progenitors and on monocytic leukemia cells induced by avian 'myeloblastosis' virus (AMV) when exposed to formaldehyde-fixed AMV leukemic cells. The CSF was assayed under serum-free conditions. Of several normal cell types tested including populations enriched for blast cells, only macrophages exhibited this capacity.