A number of cell lines both finite and continuous are developed from human tissues as well as other animal tissues. Continuous cell lines are developed originally from tumor tissues. Cell lines are characterized before preserving or distributing them for further research work. A cell line can multiply and divide to form seed stock and also working (distribution) stock.
Seed stock Culture of Cell Lines:
Animal cell lines characterized and then maintained in liquid nitrogen is called as seed stock. This seed stock is also used to produce a large quantity of distribution stock. Working or distribution stock consists of cells produced from the seed stock and some are used for further research. Cell lines are preserved using a cryopreservative agent such as glycerol or DMSO. These compounds help in minimizing the cell injury which may occur during freezing or thawing of these cells. Most of the animal cell lines are stored for a long period of time by following appropriate procedure.
Large Scale Culture of Cell Lines:
Large scale cultures of animal cell lines are produced using fomenters of up to 10,000 litters. These large scale cell lines are used for producing pharmaceutically important products such as interferons, interleukins, hormones, and also to produce vaccines against polio, mumps, measles, rabies and much more.
The scaling up of animal cell culture can be done as monolayer culture or suspension culture or as immobilized cell system. For large scale culture of animal cell lines bioreactors are used such as stirred bioreactors, airlift fomenters and much more.
Stirred bioreactors are glass or stainless steel vessels of up to ten thousand litter capacity. These bioreactors are closed systems and are agitated using stirrers connected to the motors. To maintain the temperature of these bioreactors water jacket is also placed around the reactor. Curved bottom also minimizes the cell damage, which may occur during stirring process.
Namalva cells are culture in this type of bioreactors and are used to produce interferons in large quantity. Hybridoma cells are also cultured in these bioreactors for the production of monoclonal antibodies.
Continuous Flow Culture:
Animal cell in the beginning is cultured as a batch culture. These culture system are either chemostat or turbidostat type. In chemostat type of bioreactor, some nutrient compounds like vitamin act as growth limiting factor. Fresh animal cell culture media is added after every 24-48 hours of cell growth and also equal quantity of the culture is also withdrawn from the vessel.
In turbidostat method cells grow to a predefined density. At this time, fixed volume of animal cell culture is withdrawn from the bioreactor and also same amount of fresh animal cell culture media is added, this helps in lowering the turbidity of cell culture. Then once again animal cells grow and proliferate in culture medium to reach predefined density, once again the fixed amount of culture is withdrawn and same amount of fresh culture media is added into the bioreactor.
The continuous flow culture, both types provide a continuous source of animal cells and used for the production of biochemical compounds, such as production of large quantity of viruses and interferons. Usually two stage system is used to produce large quantities of commercially important pharmaceutical compounds.
This type of fermenter uses air bubbles for agitation so the name airlift fermenters. Animal cell cultures in airlift fermenters are agitated and also aerated by the air bubbles which are introduced from the bottom of the vessels. Airlift fermenter has got an inner draft tube via which air bubbles and also the aerated medium rise because aerated medium is lighter than the non aerated ones, this helps in mixing of the cell culture and also aerate the medium.
The introduced air bubbles travel till the top of the fermenter and then it passes out through an outlet. Animal cell culture medium and also the culture media get circulated throughout the fermenter. In this type of fermenter oxygen supply is very efficient but scaling up of the animal cell culture posses some problems.
Airlift fermenters are used for the production of monoclonal antibodies in large quantity.
Animal cell lines can be maintained using cryopreservation technique and seed culture can be scaled up using airlift fermenter, continuous flow culture or by using stirred bioreactors. Scaled up animal cell culture can be used in the production of antibody, interferons and much more pharmaceutically important compounds.
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