Activation of antitumor cytotoxicity of human blood mononuclear cells by a basic factor from dialysable human-leukocyte extract

Dialysable human leukocyte extract (10 kDa molecular weight cutoff) contained a basic factor stimulating natural killer (NK) cytotoxicity of human peripheral blood mononuclear cells (PBMC) against human K562 tumor cells when PBMC were pre-incubated with the factor for 72h prior to cytotoxicity assays. This cytotoxicity-stimulating factor (CySF-L2) could be enriched by adsorption to ion exchange resin Dowex 50WX2 (H-form) eluting at pH 9.0-9.6 when a pH gradient between pH 3 and pH 10 was used. Further purification was achieved by chromatography on DEAE-Sepharose. The factor has a molecular weight of approximately 1000 Da and is insensitive to protease and exopeptidase treatment but sensitive against treatment with endoglycosidase F. Using immunomagnetic cell sorting, complement-mediated cell depletion and depletion by planning, the cytotoxic effector cells activated during pre-incubation of PBMC with CySF-L2 could be identified as CD16+ CD14+ monocytes/macrophages and as Leu7+ Leu19+ CD16+ CD3- CD8- NK cells