Cell culture types

Primary cell cultures are those that have undergone little or no mitotic division following the seeding of cells harvested directly from the tissue of origin. Tissue source for the majority of primary cell cultures is either laboratory animals (e.g. monkey kidney cells) or human pathology specimens (e.g.  Human amnion cells).  Tissue samples are incubated with a proteolytic enzyme (usually trypsin) to produce a single-cell suspension.  The harvested cells are then seeded into appropriate flasks with suitable medium. Cells in culture usually show epithelial (cuboid-shaped) or fibroblastic (spindle-shaped) morphology, and as it is usual for primary cultures to contain more than one cell type, they also usually show both morphological types. Primary cultures are sensitive to a wide range of viruses and are routinely used in diagnostic laboratories for growth of fresh virus isolates (from patients). However, primary cells frequently alter after only a few divisions, and many die or lose their ability to support virus replication. Hepatocytes are a good example; they are the natural target of hepatitis C virus infection in the body, but primary hepatocyte cell cultures do not support replication of this virus.

Many cells in culture will continue to divide for more than four to five generations, giving rise to a cell line but will eventually die after a certain number of generations, as the cells reach the Hayflick limit.  These cell lines, usually referred to as diploid cell lines, have the normal chromosome number. Continuous or immortal cell lines are capable of potentially limitless mitosis in culture, dividing through hundreds of generations. Such cell lines are either derived from tumor cells or have undergone transformation during the process of culturing, perhaps spontaneously or as a result of deliberate chemical or viral treatment. These cells are heteroploid, meaning they have aberrant chromosome number, which is usually linked to their transformed character.