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Target cell-induced calcium signals in human natural killer leukemia cells as revealed by confocal fluorescence
Y Kobayashi1, T Yamashiro, T Jinnai
1Faculty of Science, Toho University, Funabashi, Chiba, Japan.
Abstract:
The target cell-induced calcium response in natural killer (NK) cells was examined using indo-1 (a ratiometric fluorochrome), a newly developed video-rate ultraviolet laser-scanning confocal microscope system, and a human NK leukemia cell line, YTN. Susceptible target cells (JY cells), but not unsusceptible target cells (K562 cells), increased the intracellular calcium concentration ([Ca]i) in almost all indo-1-loaded YTN cells with a lag time, although the kinetics of increase in [Ca]i differed in individual YTN cells. The increase in [Ca]i was completely blocked by 2 mM EGTA and partially (around 50%) blocked by 10 microM nicardipine, the extents of inhibition of calcium response correlating well with those of inhibition of cytotoxic activity. Thus, the calcium response in YTN cells observed in this study may constitute a critical step in the manifestation of cytotoxic activity.
Insights
Natural killer (NK) cells showed a calcium response when encountering susceptible target cells. This calcium influx is crucial for NK cell cytotoxic activity, as blocking it inhibits killing.
Area of Science:
- Immunology
- Cell Biology
- Biophysics
Background:
- Natural killer (NK) cells are crucial for innate immunity, mediating target cell lysis.
- Intracellular calcium concentration ([Ca]i) dynamics are implicated in immune cell activation.
- Understanding NK cell activation mechanisms requires detailed analysis of signaling pathways.
Purpose of the Study:
- To investigate the calcium response in human NK leukemia (YTN) cells upon interaction with target cells.
- To elucidate the role of intracellular calcium increase in NK cell-mediated cytotoxicity.
Main Methods:
- Utilized indo-1 fluorochrome for ratiometric calcium imaging.
- Employed a novel video-rate ultraviolet laser-scanning confocal microscope system.
- Co-cultured YTN cells with susceptible (JY) and unsusceptible (K562) target cells.
Main Results:
- Susceptible target cells induced a significant increase in [Ca]i in YTN cells.
- Unsusceptible target cells did not elicit a comparable calcium response.
- EGTA and nicardipine treatments inhibited both calcium response and cytotoxic activity, indicating a correlation.
Conclusions:
- The observed calcium response in YTN cells is directly linked to their cytotoxic function.
- Intracellular calcium mobilization is a critical signaling event in NK cell-mediated killing.
- This study provides insights into the molecular mechanisms underlying NK cell activation.