preference, since it is argued that primary cultures retain their characteristics and
reflect the true activity of the cell typein vivo. The disadvantage in using primary
cultures, however, is that their isolation can be labour-intensive and may produce
a heterogeneous population of cells. Moreover, primary cultures have a relatively
limited lifespan and can be used over only a limited period of time in culture.
Primary cultures can be obtained from many different tissues and the source of
tissue used generally defines the cell type isolated. For instance, cells isolated from the
endothelium of blood vessels are referred to as endothelial cells whilst those isolated
from the medial layer of the blood vessels and other similar tissues are smooth muscle
cells. Although both can be obtained from the same vessels, endothelial cells are
different in morphology and function, generally growing as a single monolayer
characterised by a cobble-stoned morphology. Smooth muscle cells on the other hand
are elongated, with spindle-like projections at either end, and grow in layers even
when maintained in culture. In addition to these cell types there are several other
widely used primary cultures derived from a diverse range of tissues, including
fibroblasts from connective tissue, lymphocytes from blood, neurons from nervous
tissues and hepatocytes from liver tissue.2.5.2 Continuous cell lines
Cell lines consist of a single cell type that has gained the ability for infinite growth.
This usually occurs after transformation of cells by one of several means that include
treatment with carcinogens or exposure to viruses such as the monkey simian virus 40
(SV40), Epstein–Barr virus (EBV) or Abelson murine leukaemia virus (A-MuLV)
amongst others. These treatments cause the cells to lose their ability to regulate
growth. As a result, transformed cells grow continuously and, unlike primary culture,
have an infinite lifespan (become ‘immortalised’). The drawback to this is that trans-
formed cells generally lose some of their originalin vivocharacteristics. For instance,
certain established cell lines do not express particular tissue-specific genes. One
good example of this is the inability of liver cell lines to produce clotting factors.
Continuous cell lines, however, have several advantages over primary cultures, not
least because they are immortalised. In addition, they require less serum for growth,
have a shorter doubling time and can grow without necessarily needing to attach or
adhere to the surface of the flask.
Many different cell lines are currently available from various cell banks, which
makes it easier to obtain these cells without having to generate them. One of the
largest organisations that supplies cell lines is theEuropean Collection of Animal
Cell Cultures(ECACC) based in Salisbury, UK. A selection of the different cell lines
supplied by this organisation is listed in Table 2.1.2.5.3 Cell culture media and growth requirements for animal cells
The cell culture medium used for animal cell growth is a complex mixture of nutrients
(amino acids, a carbohydrate such as glucose, and vitamins), inorganic salts (e.g.
containing magnesium, sodium, potassium, calcium, phosphate, chloride, sulphate,50 Cell culture techniques