An autocrine growth factor constitutively produced by a human lymphoblastoid B-cell line is serologically related to lymphotoxin (TNF-beta).

Conditioned medium of a human lymphoblastoid B-cell line RPMI-6410t contains a factor sufficient for maintainance and growth of these cells. At the same time RPMI-6410t cells secrete a soluble factor cytotoxic towards mouse L929 cells. Production of these activities by RPMI-6410t cell line and its subclones is significantly enhanced after activation with phorbol mirystate acetate (PMA). Both activities can be neutralized by antiserum raised against recombinant lymphotoxin (rTNF-beta) but not by antibodies against tumor necrosis factor (rTNF-alpha). Northern analysis showed the presence of lymphotoxin mRNA which is further induced after PMA treatment. These data suggest that both autocrine growth factor and cytotoxic activities correspond to the same molecule(s) probably identical to 25 kD lymphotoxin (TNF-beta).