46
A . M O S C O N A , O . A . T R O W E L L A N D E . N . W l L L M E R
sedimentation in a gradient of increasing concentration of these substances. This has been found to be very satisfactory, for example, in
facilitating the separation of the monocytes from the blood (Weiss and
Fawcett, 1953).
Attempts to separate different classes of cells by electrophoresis have
not so far proved to be very practicable, though the electrical mobilities
of different classes of cells do differ, and normal and malignant cells
from the same tissue behave very differently (Abercrombie and Ambrose,
1962).
When tissues as such are explanted, it is sometimes possible to
obtain what is apparently a pure line of cells from what was initially
a mixed population. For example, several sorts of epithelia, because
they grow as uniform sheets of cells, can often be subcultured independently of other cells although, owing to the composite character
of most epithelia in the body, it remains doubtful whether such epithelial sheets consist of a single type of cell only. The epithelium of the
stomach, for instance, grows as an apparently uniform sheet of cells and
it is not clear to what extent the various cell types, e.g. mucous, peptic,
oxyntic, etc., contribute to the outgrowth. Pure cultures of certain
epithelia, free from mesenchymal cells, can be obtained by treating
mixed cultures with certain malt extracts of which the active principle
appears to be hexenolactone (Heaton, 1926; Medawar, 1937; Medawar
Robinson and Robinson, 1943). This substance inhibits mesenchymal
cells but does not interfere with epithelial growth. Apparently pure
sheets of kidney epithelia have been obtained in this way—but, again,
kidney tubules normally have many types of cells and it it not clear
which of these are represented in the cultures.
When mesenchymal tissues are grown, many of them eventually
yield what appear to be uniform populations of fibroblasts or mechanocytes, but the same difficulty arises as with epithelia: it is not certain
whether this apparently uniform population consists of only one sort of
cell or is in fact a mixture of cells derived from mesenchymal cells of
various sorts. For example, a culture from a blood-vessel wall could
certainly contain endothelial cells, fibroblasts, and plain muscle cells,
and possibly other types also. Problems of cell identification in cultures
are discussed further in Chapter 4.
With cultures of some bacteria and protozoa it is possible to obtain
pure cultures of one type because that type overgrows all others, and
it was at one time thought that similar methods might be applied to
tissue cells; it may indeed be possible but the difficulty of identifying
cell types in culture with any certainty makes this method at present
impracticable. The other alternative, namely that of starting cultures
from single cells has therefore been attempted.
A . M O S C O N A , O . A . T R O W E L L A N D E . N . W l L L M E R
sedimentation in a gradient of increasing concentration of these substances. This has been found to be very satisfactory, for example, in
facilitating the separation of the monocytes from the blood (Weiss and
Fawcett, 1953).
Attempts to separate different classes of cells by electrophoresis have
not so far proved to be very practicable, though the electrical mobilities
of different classes of cells do differ, and normal and malignant cells
from the same tissue behave very differently (Abercrombie and Ambrose,
1962).
When tissues as such are explanted, it is sometimes possible to
obtain what is apparently a pure line of cells from what was initially
a mixed population. For example, several sorts of epithelia, because
they grow as uniform sheets of cells, can often be subcultured independently of other cells although, owing to the composite character
of most epithelia in the body, it remains doubtful whether such epithelial sheets consist of a single type of cell only. The epithelium of the
stomach, for instance, grows as an apparently uniform sheet of cells and
it is not clear to what extent the various cell types, e.g. mucous, peptic,
oxyntic, etc., contribute to the outgrowth. Pure cultures of certain
epithelia, free from mesenchymal cells, can be obtained by treating
mixed cultures with certain malt extracts of which the active principle
appears to be hexenolactone (Heaton, 1926; Medawar, 1937; Medawar
Robinson and Robinson, 1943). This substance inhibits mesenchymal
cells but does not interfere with epithelial growth. Apparently pure
sheets of kidney epithelia have been obtained in this way—but, again,
kidney tubules normally have many types of cells and it it not clear
which of these are represented in the cultures.
When mesenchymal tissues are grown, many of them eventually
yield what appear to be uniform populations of fibroblasts or mechanocytes, but the same difficulty arises as with epithelia: it is not certain
whether this apparently uniform population consists of only one sort of
cell or is in fact a mixture of cells derived from mesenchymal cells of
various sorts. For example, a culture from a blood-vessel wall could
certainly contain endothelial cells, fibroblasts, and plain muscle cells,
and possibly other types also. Problems of cell identification in cultures
are discussed further in Chapter 4.
With cultures of some bacteria and protozoa it is possible to obtain
pure cultures of one type because that type overgrows all others, and
it was at one time thought that similar methods might be applied to
tissue cells; it may indeed be possible but the difficulty of identifying
cell types in culture with any certainty makes this method at present
impracticable. The other alternative, namely that of starting cultures
from single cells has therefore been attempted.