Effects of osmotic pressure on production of recombinant human granulocyte-macrophage colony stimulating factor in plant cell suspension culture

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a cytokine that stimulates the production of granulocytes, macrophages, and white blood cells. The effects of osmotic pressure on secretion of human GM-CSF into the culture medium were investigated in suspension cultures of transgenic tobacco cells. An increase in osmotic pressure caused by the addition of mannitol decreased the cell size index, with the effect being more pronounced when cells were measured wet rather than dry. Increased osmotic pressure enhanced the secretion of hGM-CSF. At 90 g/liter mannitol, the maximum concentration tested, hGM-CSF was present in the culture medium at 980 μg/liter. As the concentration of mannitol increased, the total amount of protein secreted also increased, but was disproportionately enriched in GM-CSF. NaCl, another osmoticum, had very similar effects on cell growth and hGM-CSF production, but did not cause enrichment for hGM-CSF.