Serum-Mediated Modification of Proliferation in Factor-Dependent Macrophage Cell Lines

Previously we described that bacterial lipopolysaccharide (LPS) promoted DNA synthesis and supported the cell viability in the factor-dependent macrophage cell lines BDM-1 and BDM-1W3 in the absence of colony-stimulating factor (CSF). To further examine this phenomenon, in the present study we examined the effects of serum on CSF-dependent proliferation and LPS-induced DNA synthesis in BDM-1 and BDM-1W3 cells. Fetal calf serum (FCS) was required for CSF-dependent proliferation in BDM-1 and BDM-1W3 cells. FCS was also required for LPS-induced DNA synthesis in BDM-1W3 cells. However, at concentrations higher than 0.2%, FCS inhibited LPS-induced DNA synthesis in BDM-1W3 cells in a dose-dependent manner. To obtain the inhibitory activity in FCS (FCS-In) for LPS-induced DNA synthesis, FCS was fractionated by gel filtration chromatography using Sephacryl S-200, chromatography on DEAE-Sephacel, and affinity chromatography on heparin-Sepharose. FCS-In was eluted in the void volume peak from a Sephacryl S-200 column, indicating that FCS-In has a molecular weight of more than 250, 000. The molecular weight of FCS-In was apparently 270, 000 as determined by SDS-polyacrylamide gel electrophoresis (PAGE) under non-reducing conditions. Upon reduction, four components became detectable with apparent molecular weights of 170, 000, 110, 000, 67, 000, and 30, 000. The inhibitory activity in FCS-In material was inactivated by heat and trypsin treatment. The partially purified FCS-In inhibited LPS-induced DNA synthesis in BDM-1W3 cells, but did not inhibit the proliferation of BDM-1W3 cells induced by IL-3, granulocyte-macrophage CSF (GM-CSF), or macrophage CSF (M-CSF). These results indicate that the inhibition by FCS-In is specific to LPS. Although the site and mechanism of inhibition are not known, FCS-In may function in vivo by modulating the interaction of LPS with macrophages.