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Selective natural killer resistance in a clone of YAC lymphoma cells
Abstract:
YAC lymphoma cells were treated with the mutagen N-methyl-N'-nitro-N-nitrosoguanidine and then cloned and subcloned. Of 51 clones, 3 were selected for further study. Ten-fold more natural killer (NK) effector cells were required to lyse YAC clone 6 and subclone 6-28 cells compared with clone 19 cells or the YAC parent cell line. The maximum plateau level of cytolysis of the NK-resistant (NKR) variants (20%) never approached that of the NK-sensitive (NKS) variants or YAC parental cells (60%) even after prolonged incubation (20 hr). NKR variants appeared with equal frequency (0.10) on cloning YAC cells that had not been treated with mutagen but these variants were highly unstable with respect to NK sensitivity and were not studied further. Cytolysis of both NKR and NKS lines was mediated by nylon-nonadherent asialo-GM1+ effector cells, and effectors from poly(I) . poly(C)-boosted mice preferentially lysed the NKS lines. The NKR alteration did not appear to change the NK target structure (NK-TS): (i) unlabeled NKR cells competed equally with NKS cells in reciprocal unlabeled-target competition assays; (ii) the frequency of target--effector conjugates was identical with NKR or NKS lines; and (iii) normal rabbit serum, which contains antibodies thought to react with the NK-TS, reacted equally against both NKR and NKS targets. The NKR alteration was selective for NK cells and did not result in a resistance to lysis in general; NKR and NKS variants were equally susceptible to (i) cytolysis mediated by alloimmune or lectin-dependent effector T cells and (ii) antibody- and complement-mediated lysis. These results are compatible with the hypothesis that the NKR variants have an altered acceptor site on the target cell membrane that normally binds the "lytic moiety" delivered by the effector cell.
Insights
Researchers identified natural killer (NK)-resistant lymphoma cell variants. These variants show altered target cell membranes, impacting NK cell recognition but not general lysis resistance.
Area of Science:
- Immunology
- Cell Biology
Background:
- Natural killer (NK) cells are crucial for innate immunity, mediating lysis of target cells.
- Understanding the mechanisms of NK cell recognition and target cell resistance is vital for immunotherapy.
Purpose of the Study:
- To investigate the characteristics of natural killer (NK)-resistant (NKR) lymphoma cell variants.
- To determine if the NKR phenotype affects the natural killer target structure (NK-TS).
Main Methods:
- YAC lymphoma cells were mutagenized and cloned to isolate NKR variants.
- Cytolysis assays were performed using NK effector cells to compare NKR and NK-sensitive (NKS) cells.
- Competition assays and conjugate formation studies were used to assess NK-TS interaction.
- Susceptibility to other forms of cell lysis (T cell-mediated, antibody-dependent) was evaluated.
Main Results:
- Mutagenesis yielded stable NKR variants requiring 10-fold more NK cells for lysis compared to NKS cells.
- NKR variants exhibited a maximum plateau of 20% cytolysis, significantly lower than NKS cells (60%).
- NK resistance was specific to NK cells, as variants remained susceptible to T cell-mediated and complement-dependent lysis.
- Competition assays, conjugate formation, and antibody binding indicated that the NK-TS was not altered in NKR variants.
Conclusions:
- The NKR phenotype in YAC lymphoma cells is not due to changes in the NK-TS.
- Results support a model where NKR variants possess altered membrane acceptor sites for the NK cell's lytic moiety.
- This selective resistance mechanism highlights the specificity of NK cell-mediated cytotoxicity.