Characterization of a Colony‐Stimulating Factor Produced by the Human Monocytic Leukemia Cell Line, THP‐1

The human monocytic leukemia cell line, THP‐1, acquires macrophage‐like characteristics following exposure to mezerein. Serum‐free medium conditioned by mezerein‐activated cells was observed to contain colony‐stimulating factor (CSF) activity in assays with murine bone marrow cultures. Isoelectrofocusing revealed that CSF activity displayed charge heterogeneity and migrated in a pl range of 4.4–5.3. Treatment with neuraminidase did not affect biological activity but did reduce charge heterogeneity. Reisofocusing of neuraminidase‐treated CSF revealed a peak of activity at pl 4.9. The active component was shown to be an acidic sialoglycoprotein, resistant to proteolytic cleavage but completely inactivated by 2‐mercaptoethanol. This CSF has been purified from THP‐1–conditioned serum‐free medium by preparative isoelectrofocusing, gel filtration through Sephacryl S‐200, ion exchange chromatography on DEAE‐Sephacel, neuraminidase treatment, and tris‐glycinate polyacrylamide gel electrophoresis (PAGE). Elution from SDS‐PAGE revealed a single peak of activity corresponding to an apparent molecular weight of 70,000 daltons. Preliminary characterization of the bone marrow cells in colonies showed that THP‐1 cells produced macrophage‐specific CSF.