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Double restriction in NK cell recognition is linked to transmethylation and can be triggered by asparagine-linked
Abstract:
The determinants of tumor cell susceptibility to NK cell-mediated cytolysis were analyzed in a two stage model. The binding of tumor cells to NK effectors was measured by target-effector conjugation and cold target competition in 51Cr-release assays, whereas triggering was measured by assaying phospholipid methylation in NK cells stimulated by intact targets. Representative targets could be grouped into three phenotypes based on the data. Those such as YAC 1.2 could bind and trigger NK cells whereas the mutagenized variant, YAC 6.28.8, could bind but was unable to trigger NK cells and therefore resisted lysis. The third phenotype was represented by HL-60 which could neither bind nor trigger NK cells and was therefore completely NK resistant. The oligosaccharide nature of the triggering molecules was demonstrated by showing that purified, high mannose containing, asparagine-linked oligosaccharides from tumor cell targets were potent stimulators of NK transmethylation at submicromolar levels. Tunicamycin pretreatment of target cells inhibited their triggering capacity but not their NK binding function. These results suggest a double restriction in NK specificity involving two independent but sequential stages in recognition represented in binding and triggering by asn-linked oligosaccharides on the tumor cell surface.
Insights
Tumor cells resist natural killer (NK) cell attacks through two stages: binding and triggering. Specific asparagine-linked oligosaccharides on tumor cells are key for NK cell recognition and lysis.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Natural killer (NK) cells are crucial for innate immunity, eliminating tumor cells.
- Understanding tumor cell susceptibility to NK cell-mediated cytolysis is vital for cancer immunotherapy.
Purpose of the Study:
- To elucidate the molecular mechanisms governing tumor cell recognition and lysis by NK cells.
- To identify the specific tumor cell surface molecules involved in NK cell binding and triggering.
Main Methods:
- Utilized a two-stage model analyzing NK cell-mediated cytolysis.
- Assessed target-effector conjugation and cold target competition in 51Cr-release assays for binding.
- Measured NK cell phospholipid methylation to quantify triggering.
- Investigated the role of oligosaccharides using purified components and tunicamycin treatment.
Main Results:
- Identified three tumor cell phenotypes based on NK cell interaction: binding and triggering (YAC 1.2), binding but no triggering (YAC 6.28.8), and neither binding nor triggering (HL-60).
- Demonstrated that asparagine-linked oligosaccharides, particularly high mannose types, stimulate NK cell transmethylation.
- Tunicamycin pretreatment abolished triggering but not binding, confirming the role of oligosaccharides in triggering.
Conclusions:
- NK cell specificity involves a two-stage process: initial binding followed by triggering.
- Asparagine-linked oligosaccharides on tumor cell surfaces act as critical recognition determinants for both binding and triggering stages.
- This dual recognition mechanism provides a novel target for enhancing NK cell-based cancer therapies.