Avian monocytic leukemia cells release fibroblast growth factor: implications to associated myelofibrosis.

Abstract The marrow of chicks with leukemia induced by avian ‘myeloblastosis’ virus (AMV) exhibited a 5–10-fold increase in the number of fibroblast colony-forming cells (CFU-F). The increased CFU-F correlated with a mild fibrosis which can be seen in the marrow of these animals. Fibroblast proliferation likely was not simply due to the presence of leukemic cells because addition of formaldehyde-fixed peripheral leukemic cells failed to initiate CFU-F growth. Conditioned medium (CM) from day-4 cultures of peripheral leukemic cells was markedly stimulatory to CFU-F growth. The stimulatory activity was not due to virus released from the leukemic cells as, (1) removal of virus by pelleting had no effect on the CM activity and (2) direct inoculation of CFU-F cultures with virus failed to stimulate CFU-F growth. Normal avian marrow macrophage monolayers also released high levels of a fibroblast growth factor and both the emacrophage-derived and leukemic cell-derived factors were heat-labile (65°, 30 min).