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

Tumor necrosis factor α, in the secreted as well as membrane- associated (mTNFα) form, represents a cytotoxic effector mechanism of activated macrophages; in contrast, direct evidence of the mTNFα 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 mTNFα; 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 lyric 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 TNFα Ab. Moreover, both mTNFα-expressing macrophages and CTL induced nuclear DNA fragmentation in WEHI 164 cells, which was also blocked by anti-TNFα 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 mTNFα expressed on different cell populations endowed with cytotoxic capability and also imply a role for this molecule in T-cell-mediated cytotoxicity.