Tumor-activated NK cells trigger monocyte oxidative metabolism

Area of Science:

• Immunology
• Cellular Biology
• Cancer Research

Background:

• Natural killer (NK) cells are crucial for innate immunity, recognizing and eliminating tumor cells.
• Respiratory burst, measured by chemiluminescence (CL), is an indicator of cellular oxidative activity.
• The precise cellular source of CL in NK cell and tumor cell co-cultures was previously unclear.

Purpose of the Study:

• To investigate whether tumor cells stimulate a respiratory burst in human NK cells.
• To identify the specific cell type responsible for CL generation in NK cell preparations.
• To elucidate the mechanism of monocyte activation by NK cells in the context of tumor cell interaction.

Main Methods:

• Percoll-purified NK cells were co-cultured with NK-susceptible (K562) and NK-resistant (P815) tumor cells.
• Luminol-dependent chemiluminescence (CL) was used to measure respiratory burst activity.
• Monocyte depletion (MO2 antibody and complement), nylon wool column adherence, and IL-2 culture were employed to isolate cell functions.

Main Results:

• NK cell preparations generated significant CL with K562 but not P815 tumor cells.
• CL response was dependent on NK cells but generated by contaminating monocytes, not NK cells themselves.
• Supernatants from NK/K562 incubations contained factors that stimulated monocyte CL, while superoxide anion was not required for NK cell lysis.

Conclusions:

• The respiratory burst observed in NK-enriched preparations is primarily mediated by monocytes.
• Tumor-activated NK cells release factors that trigger monocytes to produce a respiratory burst.
• This monocyte-derived respiratory burst is distinct from NK cell-mediated cytotoxicity and does not require superoxide anion.