Cell culture

Cell culture refers to the removal of cells from an animal or plant and their subsequent growth in a favorable artificial environment. That is why cell culture is always an in vitro procedure. The cells may be removed from the tissue directly and disaggregated by enzymatic or mechanical means before cultivation, or they may be derived from a cell line or cell strain that has already been established.

Primary culture

Primary culture refers to the stage of the culture after the cells are isolated from the tissue and proliferated under the appropriate conditions until they occupy all the available substrate (i.e., reach confluence). At this stage, the cells have to be subcultured (i.e., passaged) and transferred to a new vessel with fresh growth medium to provide more room for continued growth. These cells have a limited life span.

Cell line

After subculturing, the primary culture becomes known as a cell line or subclone, when the cells acquire homogenous genotypic and phenotypic characteristics. Cell lines derived from primary cultures have a limited life span (i.e., they are finite; see below), and as they are passaged, cells with the highest growth capacity predominate, resulting in a degree of genotypic and phenotypic uniformity in the population.

Cell lines can also be immortalized, when they have acquired the ability to proliferate indefinitely, either through genetic mutations or artificial modifications.

Stem cell

A stem cell is a cell that can replicate itself or differentiate into other cell types. Stem cells are unspecialized, meaning they do not have any tissue-specific structures that allow them to perform specialized functions.