PHYSICOCHEMICAL CHARACTERISTICS OF TUMOR-CELLS SUSCEPTIBLE TO LYSIS BY NATURAL KILLER (NK) CELLS

YAC-ascites tumour cells, which were grown in vitro for different lengths of time, showed a gradually increased susceptibility to lysis by natural killer (NK) cells, compared to the cell line in vivo, as measured with a 51Cr-release assay. Concomitantly the liability to hydrophobic interaction of the YAC-cells was gradually augmented, as assessed by aqueous biphasic partitioning in systems of dextran T 500 and poly-(ethyleneclycol) 6000 (PEG) with part of the PEG exchanged for hydrophobic PEG-palmitate (P-PEG). In systems containing no hydrophobic PEG the cells preferentially adhered to the interface between the top phase (rich in PEG) and the bottom phase (rich in dextran) but could be transposed towards the ton Phase by P-PEG. The affinity for P-PEG was more evident after prolonged time of cultivation in vitro. The cells could also be moved to the top phase by positively charged trimethylamino-PEG. but negligible differences were observed between the cell lines The results indicate that either a loss of hydrophilic surface constituents or exposure of new or otherwise hidden hydrophobic structures occurred on the surface of the tumour cells with increasing time of cultivation. These properties may be related to the susceptibility to lysis by NK cells. © 1979 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.