Membrane form of TNF alpha induces both cell lysis and apoptosis in susceptible target cells.

Tumor necrosis factor alpha, in the secreted as well as membrane-associated (mTNF alpha) form, represents a cytotoxic effector mechanism of activated macrophages; in contrast, direct evidence of the mTNF alpha involvement in cytotoxic T lymphocyte (CTL)-mediated lysis has not yet been obtained. We observed that following activation with anti-CD3 monoclonal antibody (mAb), both cloned CTL and peritoneal exudate lymphocytes rapidly upregulated mTNF alpha; a similar effect was observed in the macrophage cell line J774 after stimulation with lipopolysaccharide endotoxin. Activated effector cells, which were fixed with paraformaldehyde before testing, exerted lytic activity against the TNF-sensitive WEHI 164 tumor cell line, but not against the TNF-resistant P-815 mastocytoma. This effect was completely inhibited in the presence of anti-mouse TNF alpha Ab. Moreover, both mTNF alpha-expressing macrophages and CTL induced nuclear DNA fragmentation in WEHI 164 cells, which was also blocked by anti-TNF alpha Ab and was accompanied by a morphologic degeneration characteristic of the apoptotic form of cell death. These data on the whole indicate a common mode of action for mTNF alpha expressed on different cell populations endowed with cytotoxic capability and also imply a role for this molecule in T-cell-mediated cytotoxicity.