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Membrane form of TNF alpha induces both cell lysis and apoptosis in susceptible target cells
G Monastra1, A Cabrelle, A Zambon
1Institute of Oncology, Inter-University Center for Cancer Research, University of Padova, Italy.
Abstract:
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.
Insights
Membrane-associated tumor necrosis factor alpha (mTNF alpha) plays a role in cytotoxic T lymphocyte (CTL) lysis. This molecule mediates apoptosis in tumor cells, indicating a common cytotoxic mechanism across different immune cells.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Tumor necrosis factor alpha (TNF alpha) is a known cytotoxic effector from macrophages.
- The role of membrane-associated TNF alpha (mTNF alpha) in cytotoxic T lymphocyte (CTL) mediated lysis was previously unclear.
Purpose of the Study:
- To investigate the involvement of mTNF alpha in CTL-mediated cytotoxicity.
- To determine if mTNF alpha expressed on CTLs and macrophages shares a common cytotoxic mechanism.
Main Methods:
- Activation of cloned CTLs, peritoneal exudate lymphocytes, and J774 macrophages.
- Assessment of cytotoxic activity against TNF-sensitive (WEHI 164) and TNF-resistant (P-815) cell lines.
- Inhibition studies using anti-mouse TNF alpha antibody (Ab).
- Analysis of DNA fragmentation and cell morphology to identify apoptosis.
Main Results:
- Activated CTLs and macrophages rapidly upregulated mTNF alpha.
- Fixed effector cells exhibited TNF alpha-dependent lysis of WEHI 164 cells, but not P-815 cells.
- mTNF alpha-expressing cells induced DNA fragmentation and apoptotic cell death in WEHI 164 cells, an effect blocked by anti-TNF alpha Ab.
Conclusions:
- mTNF alpha is involved in CTL-mediated cytotoxicity.
- mTNF alpha expressed on both macrophages and CTLs utilizes a common mechanism to induce apoptosis in target tumor cells.
- These findings suggest a significant role for mTNF alpha in T-cell-mediated tumor cell killing.