Mammalian cell cultures. Part I: Characterization, morphology and metabolism.

Primary cell cultures are obtained by trypsinization from tissue cultures usually as a monolayer culture. The absence of fetal calf serum will support suspended growth behaviour of spontaneously transformed cells. After several passages the cell line becomes more stable and gives rise to a continuous cell line. Such continuously growing cell lines are a prerequisite for production of recombinant DNA derived proteins. Mammalian cells are 10-100 times larger in diameter than microorganisms. They have no cell wall and express therefore a higher sensitivity to hydrodynamic sheer forces. One of the most stringent problems in mammalian cell culture are "silent" contaminants with mycoplasma which might change cell growth. Mammalian cell cultures show a complex metabolism where regulation of metabolites and catabolites are not fully understood. Glucose is the main carbohydrate source. Also three groups of intercorrelated amino acids are known. Lactate as the primary metabolite of glucose and ammonia as a metabolite of glutamine are expected to be cytotoxic for mammalian cells. Although in some experiments even the addition of ammonia has no significant effect on the viability of hybridoma cells. Adherent cells can be cultivated attached to surfaces such as microcarrier or wire springs. Suspended cells are grown in stirred bioreactors with a comparable technology to fermentation of microorganism. Parameters such as pH, temperature, stirring tip speed and osmolality have to be well controlled in order to obtain high cell viability and cell density.