Murine recombinant GM-CSF-driven rat bone marrow cell differentiation and factors suppressing cell proliferation

Rat or mouse bone marrow cells (BMC) cultured for one week with a crude mouse L929 cell supernatant or with purified colony stimulating factor type 1 (CSF-1) differentiate into an essentially pure population of macrophages (M phi). Surprisingly, 90 to 95% of the cells obtained by culturing rat BMC for seven days with recombinant murine granulocyte-macrophage CSF (rmGM-CSF), regardless of concentrations, were classified as M phi. The majority of the remaining cells were granulocytes. This effect is in contrast to that on mouse BMC cultures, where the percentage of granulocytes increased with higher concentrations of rmGM-CSF. The proliferative capacity of rat BMC was demonstrated by colony formation in soft-agar, enumerating total cell number in liquid cultures or measuring 3H-thymidine uptake. A crude L929 cell supernatant and rmGM-CSF induced cell proliferation in a dose-dependent manner. Maximal DNA-synthesis was observed on the fifth day of incubation when BMC were cultured at a density of greater than or equal to 1 x 10(5) cells/well. In cultures initiated with lower cell density, prolonged DNA synthesis was observed. Thereafter, the rate of proliferation declined rapidly. Simultaneous incubation of BMC with GM-CSF and indomethacin led to increased levels of DNA synthesis, suggesting that prostaglandins may suppress cell proliferation. Furthermore, the CSF-induced BMC proliferation was dose dependently inhibited by dexamethasone and 1,25-dihydroxy-vitamin D3 as well as by interferon-gamma and tumor necrosis factor-alpha. The suppressive effect of both cytokines could be abrogated by the addition of the respective anticytokine antibodies.