Abstract
We examined the capacities of sera from patients with myeloid leukemia to induce differentiation in mouse myeloid leukemic M1 cells. Higher differentiation-inducing activity (D-activity) was detected in sera of patients with chronic myelomonocytic leukemia or chronic myeloid leukemia (CML) than in sera of patients with acute myeloid leukemia and normal volunteers. The D-activity in the sera was lost on heating the sera at 56 degrees for 30 min. The major peak of D-activity on Sephadex G-200 gel filtration had an apparent molecular weight of 160,000. The origin of the D-activity in sera of patients with CML was studied by culturing fractions of peripheral blood cells of patients with D-activity for 3 days and then measuring the ability of the conditioned medium (CM) to induce differentiation of M1 cells. The cells in the myeloblast and promyelocyte fraction differentiated spontaneously into macrophage-like cells during culture for 3 days and the cells in the late granulopoietic cell fraction differentiated into neutrophil-like cells. Higher D-activity was present in CM of cells in the myeloblast and promyelocyte fraction than in CMs of late granulopoietic cell fractions. These results suggest that human leukemic cells produce D-activity for M1 cells during their differentiation into macrophage-like cells.