Cell culture refers to the removal of cells from an animal or plant and their subsequent growth in a favorable artificial environment. 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 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 of the available substrate (i.e., reach confluence). At this stage, the cells have to be subcultured (i.e., passaged) by transferring them to a new vessel with fresh growth medium to provide more room for continued growth.
After the first subculture, the primary culture becomes known as a cell line or subclone. 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.
If a subpopulation of a cell line is positively selected from the culture by cloning or some other method, this cell line becomes a cell strain. A cell strain often acquires additional genetic changes subsequent to the initiation of the parent line.
Finite vs Continuous Cell Line
- a substrate or medium that supplies the essential nutrients (amino acids, carbohydrates, vitamins, minerals)
- gases (O2, CO2)
- a regulated physico-chemical environment (pH, osmotic pressure, temperature)
Most cells are anchorage-dependent and must be cultured while attached to a solid or semi-solid substrate ( adherent or monolayer culture), while others can be grown floating in the culture medium ( suspension culture).
Morphology of Cells in Culture
Fibroblastic (or fibroblast-like) cells are bipolar or multipolar, have elongated shapes, and grow attached to a substrate.
Epithelial-like cells are polygonal in shape with more regular dimensions, and grow attached to a substrate in discrete patches.
Lymphoblast-like cells are spherical in shape and usually grown in suspension without attaching to a surface.