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Induction of hemoglobin synthesis in K562 cells by thymidine (2 mM) in vitro did not significantly enhance major histocompatibility complex antigen-unrestricted lysis of splenocyteexposed K562 cells. Inhibition of thymidine-induced hemoglobin synthesis by simultaneous incubation of cells with thymidine and phorbol 12-myristate 13-acetate (100 nM) decreased cytolytic activity of splenocytes against K562 cells. Preincubation of tumor cells with phorbol ester alone did not affect major histoeompatibility complex antigen-unrestricted lysis induced by rat splenocytes but decreased the basal level of hemoglobin synthesis. Here we studied changes in the sensitivity of K562 cells to NCT lysis mediated by natural killer cells under conditions of induction of erythroid markers and after PMA-inhibition of induced erythroid differentiation. MATERIALS AND METHODSExperiments were performed on Wistar rats weighing 180-220 g. Spleen fragments were forced through a metal grid to obtain splenocytes. Erythrocytes were lysed with distilled water.K562 cells (All-Russian Collection of Cell Cultures, Institute of Cytology) were grown in RPMI-1640 medium (Institute of Poliomyelitis and Viral Encephalitis) containing 11% fetal bovine serum (N. F. Gamaleya Institute of Epidemiology and Microbiology), 2 mM L-glutamine, 40 gg/ml gentamicin sulfate, and 5x10 -5 M 2-mercaptoethanol (Ferak).

Experiments with human erythromyeloleukemic K562 cells as target cells demonstrate that nonspecific cytotoxic activity of rat splenocytes suppressed by 1-day incubation of cells with phorbol-12-myristate-13-acetate is restored by subsequent 3-day incubation with interleukin-2 and staurosporin. Combined effects of both drugs during this incubation time decrease cell permeability for Trypan Blue by 50%.