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.