Purification and characterization of a mouse serum protein with growth inhibitory properties in vitro against tumor cell lines.

A factor which is responsible for the growth inhibitory properties of certain mouse sera and related to NK-activity, has been studied. The factor was isolated from hybrid B6D2F1 (C57Bl/6 x DBA/2) serum, which is histo-compatible with the mouse tumour (B16 melanoma) used and has high NK-activity. Growth inhibitory activity was measured in an in vitro assay. It was independent of complement activation. The responsive factor was isolated and characterized by ion exchange chromatography. Concanavalin A affinity chromatography, gel filtration and iso-electric focusing. It appears to be a protein and had been labelled growth-inhibitory factor (GIF). It has a molecular weight of 230 000-260 000 daltons and an iso-electric point in the pH range 4.6-5.0. It was not retained on Concanavalin A columns.