Inhibition of cell growth by macrophage membrane lipid molecule

Macrophage hybridoma clone 5 suppressed B-cell proliferation induced by lipopolysaccharide (LPS). Since paraformaldehyde-fixed macrophages exerted the effect, macrophage-derived mediators were excluded from the inhibition. The inhibitory property of macrophages was present in the membrane fraction and was recovered in the organic phase after extraction using a chloroform/methanol/water system followed by hexane extraction. Therefore, the inhibitory activity found in macrophage clone 5 was concluded to arise from a lipid component. The inhibitory substance was further purified to a homogeneity by LH20 column fractionation using methanol/chloroform as the mobile phase. The purified lipid did not have any effect on the LPS-mediated induction of MHC class II molecules on the B-cell surface. Moreover, the inhibitory property was shown to affect growth of a wide variety of tumor cell lines of human origin. These results suggest that a lipid molecule found on the cell membrane of cloned macrophage hybridoma may participate in the regulation of cell growth through cell contact.