* Author for correspondence Summary

The purpose of the present investigation was to optimize the culture conditions in suspension of the HL-60 cell line for high-density production. The optimized HT. medium was a mixture of RPMI-1640, DMEM, HamF12 and IMDM media supplemented with transferrin, insulin, Primatone RL, Pluronic F68, ethanolamine and selenite. Under these con-ditions, whether serum was added or not, cells grew to up to 8xl06cellsml"1, which was at least three times higher than the maximum cell density usually described. Glucose and four amino acids: cystine, glutamine, methionine and serine, were highly con-sumed and disappeared quickly from the medium. Nutrient supply and metabolic end-product accumu-lation were the most probable growth-limiting fac-tors. Different propagation systems were used to increase the cell density further. Cells were grown in dialysis tubing where relatively high levels of nutri-ents and low levels of waste products were main-tained, leading to cell densities of 60xl06 to 70x10 cells ml"1. A perfusion-culturing method with cell retention was found to be most effective for high-density production of HL-60 cells at a 21 as well as a 601 fermentor scale. Average concentrations of 40xl06 to 50xl08 cells ml"1 were achieved. Ex-pression and distribution of both tumor necrosis factor receptors (55 and 75xlO3Mr) on the surface of HL-60 ^ells were analysed as a control of the physiological integrity of the cells during the perfu-sion course; 1.3 /Jg of tumor necrosis factor receptors/1010 cells was regularly expressed on the surface of HL-60 cells. Key words: HL-60, proliferation, high cell density, tumor necrosis factor receptors