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We have previously reported that a lipid molecule in the membrane fraction of cloned macrophage hybridomas inhibited the growth of lymphocytes and several tumor cell lines. In this study, the inhibitory lipid molecule in the membrane fraction of macrophages was analyzed by thin–layer chromatography and identified as 25–hydroxycholesterol, a family of oxysterols. This conclusion was confirmed by analysis using gas chromatography–mass spectrometry. In addition, both 25–hydroxycholesterol and the lipid molecule recovered from macrophage cell membrane induced apoptosis of the murine T cell lymphoma, BW–5147. These results suggest that an oxysterol expressed in the macrophage cell membrane may participate in the regulation of cell growth through cell contact. [ABSTRACT FROM AUTHOR]

We have previously reported that the growth of lymphocytes and tumor cells with lymphocyte lineage was strongly inhibited by a part of cloned macrophage hybridomas. This growth inhibition was accomplished by cell-to-cell contact and found to be attributed to lipid-like molecule(s) in a macrophage hybridoma cell membrane fraction. Instead of macrophage hybridomas, in the present study we utilized splenic adherent cells (SACs) that had been stimulated with IFN-γ to see whether they inhibited tumor cell growth or not. The results demonstrated that IFN-γ-stimulated but not unstimulated SACs showed a significant growth inhibition of BW-5147 tumor cells. This growth inhibition was not mainly mediated by prostaglandin E[sub 2] secreted from macrophages, since the inhibition was not reduced in the presence of indomethacin. Furthermore, as was reported previously in the case of macrophage hybridomas, the inhibitory activity resides in a lipid fraction of IFN-γ-stimulated SAC membrane. [ABSTRACT FROM AUTHOR]