<P> Cells that are cultured directly from a subject are known as primary cells . With the exception of some derived from tumors, most primary cell cultures have limited lifespan . </P> <P> An established or immortalized cell line has acquired the ability to proliferate indefinitely either through random mutation or deliberate modification, such as artificial expression of the telomerase gene . Numerous cell lines are well established as representative of particular cell types . </P> <P> For the majority of isolated primary cells, they undergo the process of senescence and stop dividing after a certain number of population doublings while generally retaining their viability (described as the Hayflick limit). </P> <P> Cells are grown and maintained at an appropriate temperature and gas mixture (typically, 37 ° C, 5% CO for mammalian cells) in a cell incubator . Culture conditions vary widely for each cell type, and variation of conditions for a particular cell type can result in different phenotypes . </P>

Difference between cell line cell strain and cell type