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Active tumor cell resistance to human natural killer lymphocyte attack
Abstract:
Inhibition of protein synthesis by cycloheximide, puromycin, or emetine increased tumor lysis mediated by human natural killer (NK) cells to "slow" but not "fast" tumor targets. Human T24 bladder carcinoma cells were used as slow targets which are killed after a approximately 3-hr lag period, and K562 cells derived from a patient with myelogenous leukemia were used as fast targets which are killed without a lag period. This enhancement of killing exceeded that which would have been expected simply from a reduction of tumor cell growth during the time of assay. Pretreatment of the NK effector cells and the tumor cells separately showed that the effect was on the tumor cells and not due to enhancement of NK cell activity. These observations imply that some tumor cells can actively resist NK attack. The discovery that some but not all human tumor cells actively resist cellular immune attack, perhaps by repair mechanisms dependent upon protein synthesis, provides a new model for evaluation of tumor cells in their resistance to host defenses.
Insights
Inhibiting protein synthesis in tumor cells enhances natural killer (NK) cell attacks on slow-growing targets. This suggests tumor cells may actively resist immune defenses through protein-dependent repair mechanisms.
Area of Science:
- Immunology
- Cancer Biology
- Cellular Biology
Background:
- Natural killer (NK) cells are crucial for innate immunity against tumors.
- Tumor cells exhibit varying susceptibility to NK cell-mediated lysis.
- Mechanisms of tumor resistance to NK cell attack are not fully understood.
Purpose of the Study:
- To investigate the role of protein synthesis in tumor cell resistance to NK cell-mediated lysis.
- To determine if inhibiting protein synthesis affects NK cell activity or tumor cell susceptibility.
- To identify potential mechanisms by which tumor cells evade immune surveillance.
Main Methods:
- Human T24 bladder carcinoma (slow target) and K562 leukemia (fast target) cells were utilized.
- Protein synthesis inhibitors (cycloheximide, puromycin, emetine) were applied to tumor cells.
- NK cell-mediated cytotoxicity assays were performed.
- Tumor cells and NK effector cells were pretreated separately to discern the site of action.
Main Results:
- Inhibition of protein synthesis significantly increased NK cell-mediated lysis of slow targets (T24 cells).
- Fast targets (K562 cells) did not show increased lysis upon protein synthesis inhibition.
- The effect was localized to the tumor cells, not due to enhanced NK cell activity.
- Enhanced lysis exceeded that attributable to reduced tumor cell proliferation.
Conclusions:
- Certain human tumor cells possess active resistance mechanisms against NK cell attack.
- Protein synthesis appears to be involved in these tumor cell resistance pathways.
- This finding provides a novel model for assessing tumor cell resistance to host immune defenses.