Production and induction of a novel cytotoxin (factor 2) by a human B-cell line

The human B-cell line, Karpas 160, was found to produce Factor 1 and 2 (F1 and F2). F1 was found to be indistinguishable from tumor necrosis factor beta (TNF-beta), while F2 appears to be a new cytotoxin. We used several stimuli alone or in combination to trigger the 160b cells, a subclone of Karpas 160, to produce higher yield of F2. The optimal culture times, concentrations of cells and a range of stimuli were studied. We found that 20-25 ng/ml of phorbol myristate acetate (PMA) effectively induced the higher production of F2. Pretreatment of the cells with sodium butyrate enhanced F2 production. Production of TNF but not F2 was inhibited when the cells were cultured with tunicamycin and PDB. When ciprofloxacin or cycloheximide was added to the medium, F2 production in the presence of PMA was amplified. When 160b cells were cocultured with K562 cells, low levels of F2 induction were observed. We found that most types of human tumor cell lines were highly susceptible to F2, but less sensitive or even resistant to TNF. In contrast, normal human cell lines were not susceptible to F2. Therefore, it appears that F2 could be a new human cytotoxin.