Maintenance of Adherent Cell Lines, Heterogeneous Primary Culture, Cell Strain, Cell Lines, Homogeneous

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	Maintenance of Adherent Cell Lines - When a primary culture produced on a substrate or in suspension (as discussed above) has increased to the extent that all the available substrate is occupied or the medium largely consumed, there arises the need to subculture it.
From a very heterogeneous primary culture containing many types of cells derived from the original tissue, during sub culturing (passages or transfer) a more homogeneous 'cell line' emerges (as discussed above). The culture now called a cell line, can be propagated, characterized and stored. The potential increase in cell number and uniformity of cells, open up a much wider range of possibilities. The term' cell line implies the presence of several cell lineages either similar or distinct. Among these cell lineages, if a particular cell lineage has specific properties, which are identified in bulk of the cells of that culture, it is described then as a cell strain'. A "cell line" or 'cell strain' may be finite or continuous, depending upon whether it has limited culture life spans or it is immortal in culture. Finite cell lines grow upto 20-80 population doublings before extinction. Some commonly used cell lines and cell strains and a comparison of the properties of mite and continuous cell lines is presented.