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Cholera toxin inhibits lethal hit stage of natural killer cell-mediated cytotoxicity
M Watanabe1, T Kiyohara, K Murata
1Department of Pathology, Nagasaki University, Japan.
Abstract:
Cytolytic process which was affected by cholera toxin (CT) resulting in the loss of natural killer (NK) cell activity was analyzed. Conjugate formation assay, membrane phospholipid methylation assay and serine esterase (granzyme A) release assay were used to determine the stage of the CT-induced inhibition of NK cell-mediated cytotoxicity. A human NK cell line YT cell-mediated cytotoxicity was completely abolished by CT pretreatment or addition of CT to the assay system. The conjugate formation assay revealed that the binding between YT cells and target cells was not affected by CT. The defined triggering stage which is coupled with membrane phospholipid methylation was not affected by CT treatment, either. On the other hand, the lethal hit stage which is represented by serine esterase (SE) release was completely inhibited by CT treatment of YT cells. Therefore, CT inhibits the stage after binding and triggering--i.e., lethal hit stage of NK cell-mediated cytotoxicity. The results also suggest that there exists a CT-sensitive negative cytotoxic signal transduction pathway as well as usual positive signal transduction pathway and these pathways might cross talk each other in the NK cell cytotoxic process.
Insights
Cholera toxin (CT) inhibits natural killer (NK) cell activity by blocking the lethal hit stage, not cell binding or triggering. This suggests a CT-sensitive pathway negatively regulates NK cell cytotoxicity.
Area of Science:
- Immunology
- Cellular Biology
- Molecular Signaling
Background:
- Natural killer (NK) cells are crucial for innate immunity, mediating cytotoxicity against target cells.
- Cholera toxin (CT) is known to affect various cellular processes, but its precise impact on NK cell cytotoxicity requires elucidation.
Purpose of the Study:
- To investigate the specific stage of NK cell-mediated cytotoxicity inhibited by cholera toxin (CT).
- To determine the mechanism by which CT affects NK cell cytotoxic function.
Main Methods:
- Utilized conjugate formation assays to assess cell-to-cell binding.
- Employed membrane phospholipid methylation assays to evaluate the triggering stage.
- Measured serine esterase (SE) release to determine the lethal hit stage of cytotoxicity.
Main Results:
- CT completely abolished NK cell-mediated cytotoxicity in the human NK cell line YT.
- CT did not affect the conjugate formation (binding) or triggering stages.
- CT significantly inhibited the lethal hit stage, specifically the release of serine esterase.
Conclusions:
- Cholera toxin inhibits NK cell cytotoxicity at the lethal hit stage, after initial binding and triggering.
- A CT-sensitive negative signal transduction pathway likely exists and may interact with positive pathways in NK cell cytotoxicity.