A selective inhibitor of cell proliferation from normal serum.

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Abstract
A factor in normal serum that selectively and reversibly inhibits proliferation of cells in culture was enriched 160-fold from calf serum by sequential ammonium sulfate precipitation, gel filtration and lectin-affinity chromatography. DNA synthesis of normal (but not transformed) rat hepatocytes [K22 and K16 cells], human lymphoblast lines [WiL2 and 8866 cells] and mitogen-stimulated murine spleen cells is inhibited by > 90%, and Vero [African green monkey kidney cells], murine myeloma [murine erythroleukemia cells], and a human colon carcinoma cell line [LS174T] to a lesser extent. Growth of other cell lines tested was not affected. Responsive cells are arrested apparently in G1 by this inhibitor, the effect of which is maximal by 24 h and is spontaneously reversible thereafter unless it is renewed. The active fraction is a protein that migrates with the .alpha.2-globulins; it is not a lipoprotein, and it is of high apparent MW.