Biochemical and biological characterization of a Multi-CSF constitutively produced by a murine tumor cell line and distinct from IL-3

The authors have identified and characterized a multiple colony stimulating factor, distinct from IL-3 (Multi-CSF), secreted by the alveologenic adenocarcinoma LT-85. The active factor in LT-85 conditioned medium (LT-85 CM) was found to be a heat stable glycoprotein that eluted from a TSK G3000SW column at a molecular weight of 40,000-60,000 and < 100,000 daltons. Polyacrylamide gel electrophoresis of 35S-methionine-labeled LT-85 CM established the monomeric molecular weight of the factor at 55,000 daltons. No band was detected in the molecular weight range reported for IL-3 (23-28,000). Like IL-3, the LT-85 CM stimulated formation of granulocyte-macrophage, megakaryocyte, and erythroid colonies from mouse bone marrow (BM) precursor cells cultured in vitro. In addition, increased DNA synthesis was demonstrated by 3H-thymidine incorporation when mouse spleen or BM cells were incubated in the presence of LT-85 CM. Selective depletion of T and/or B cells from the spleen cell population did not affect thymidine incorporation. LT-85 CM did not, however, support the growth of the IL-3-dependent cell line DA-1. Supernatant from bone marrow cells incubated in the presence of LT-85 CM also failed to support the growth of DA-1 cells or stimulate DNA replication. Finally, preincubation of donor BM cells with LT-85 CM for 48 hours prior to transfer significantly enhanced engraftment of bone marrow cells in lethally irradiated mice. These data suggest that the Multi-CSF activity of LT-85 CM accelerates maturation of BM cells both in vitro and in vivo