In Vitro Production of Lymphocyte and Granulocyte Proliferation Inhibitors (chalones?) from Living Cells

Media conditioned with viable rat and calf spleen lymphocytes were seen to be able to inhibit 3H-thymidine uptake by rat thymocytes and the mitogenic response of human lymphocytes to PHA but not bone marrow cells proliferation. The inhibitor appeared to have a molecular weight greater than 50,000 daltons, as determined by Amicon Diaflo ultrafiltration. Media conditioned with rat granulocytes had a similar tissue specific but species non-specific inhibitory action. Also human leukemic cells appeared able to produce in vitro an inhibitor of cell proliferation when a certain degree of differentiation was present.