[Effect of gangliosides on the cytotoxic activity of natural killers from Syrian hamsters].

The ability of various gangliosides to inhibit the cytotoxic activity of natural killers (NK-cells) from Syrian hamsters towards human lymphoma MOLT-4 cells was studied. The inhibitory effect was found to depend on the structure and concentration of the gangliosides. At concentrations corresponding to those in the blood of tumour-bearing hosts, SiaLacCer and Sia2LacCer inhibited the NK-activity. A significant inhibition was also found for (NeuAc)2GgOse3Cer, whereas NeuGcGgOse3Cer and NeuAcGgOse4Cer were practically inactive. Previously it was shown that Sia2LacCer which is either absent or very low in normal blood, is produced by a number of tumours and that tumour cells "shed" considerable amounts of gangliosides. On this ground, it was proposed that elevated concentrations of SiaLacCer and Sia2LacCer in the blood of tumour-bearing animals may inhibit the NK-activity and thus contribute to the "escape" of tumour cells from host immune surveillance.