Single Degranulations in NK Cells Can Mediate Target Cell Killing

Area of Science:

• Immunology
• Cell Biology
• Cytometry

Background:

• Natural killer (NK) cells are crucial cytotoxic lymphocytes for antiviral and anticancer immunity.
• NK cell-mediated cytotoxicity involves the release of effector molecules from lytic granules at the immune synapse.
• The precise number of degranulation events necessary for NK cell-mediated killing remains undetermined.

Purpose of the Study:

• To quantify the minimum number of degranulation events required for a human NK cell to kill a target cell.
• To investigate the relationship between degranulation kinetics and NK cell killing efficiency.

Main Methods:

• High-resolution four-dimensional confocal microscopy was employed to observe human NK-target cell conjugates.
• LAMP-1-pHluorin was used as a reporter to quantify NK cell degranulation events.
• Target cell death was assessed concurrently with degranulation.

Main Results:

• An average of only two to four degranulation events were sufficient for an NK cell to induce target cell death.
• NK cells released approximately 1/10th of their lytic granules per target but required only ~1/100th to kill a target.
• Killing kinetics correlated with lytic granule size, effector molecule content, and degranulation timing.

Conclusions:

• Human NK cells achieve target cell killing with a surprisingly low number of degranulation events.
• The efficiency of NK cell killing is influenced by granule composition and the temporal dynamics of degranulation.