Characterization of a cytotoxic factor produced by rat bladder cancer cell line: its identity to TNF alpha

Clone C19 derived from a rat bladder cancer cell line BC31ad constitutively released cytotoxic factor RCF. The serum-free C19-conditioned medium was partially purified by DEAE-Sephacel, Sephacryl S-200 and MonoQ-FPLC chromatographies to the specific activity of 6.4 x 10(6) U/mg protein (LM assay). RCF was a 17-kDa protein with pI 4.6-5.0. Anti-RCF serum neutralized the cytotoxic activity of rat and mouse, but not human, tumor necrosis factor-alpha (TNF alpha) as well as RCF. The partial amino acid sequence of RCF was homologous with the sequence 43-58 of rat TNF alpha. RCF and rat TNF alpha showed a similar cytotoxic spectrum against several tumor cells. Furthermore, they induced a marked proliferation of mouse T cells in combination with a suboptimal dose of ConA or anti-CD3 antibody, however, human TNF alpha almost not. Taken together, RCF was substantially regarded as rat TNF alpha.