Biology Reference
In-Depth Information
10.2 METHODS TO MEASURE CELL ADHESION
Different assays have been developed to qualitatively and quantitatively
study cell adhesion. Usually, these assays probe the ability of cells to remain
attached to an adhesive substrate when exposed to a certain detachment
force. This adhesive substrate can be another cell, a surface or an organic
matrix. Adhesion assays can be classiied into
bulk
or
single-cell
assays.
10.2.1 Bulk Assays
The most commonly used bulk assay to study cell adhesion is the washing
assay. In this assay, cells are seeded onto an adhesive substrate of interest,
allowed to adhere for a given time and rinsed with physiological buffer.
Thereby, non- or weakly attached cells are dislodged from the substrate
and the fraction of attached cells is determined.
9-12
Washing assays are
hardly reproducible since the applied shear forces are unknown, unevenly
distributed and dificult to control. Moreover, washing assays can hardly
provide quantitative information about cell adhesion strengths or energies.
Reproducible results that qualitatively describe cell adhesion have been
obtained using parallel plate chamber setups, spinning disc devices
13
or
centrifugation assays.
14,15
However, these techniques also have limitations
since the resistance of cells to detachment by hydrodynamic or centrifugal
forces depends not only on the number, distribution and strength of the
formed adhesion bonds, but also on the spread area and surface topography
of the cells. Thus, with these assays, the adhesive strength of cells can only
be estimated.
On the other hand, using bulk assays, statistically relevant data can be
easily obtained as large numbers of cells are tested in each experiment.
However, these assays only analyze the average behaviour of large cellular
populations. Therefore, they are rather constricted in determining potential
differences in the adhesion of individual cells. Adhesive subpopulations
might result from different functional states of individual cells. Such valuable
information can be easily missed in bulk assays.
10.2.2 Single-Cell Assays
For a more quantitative approach, techniques that measure the adhesion of
single cells are needed. Compared with bulk assays, SCFS assays are usually
time-consuming, since only a single cell is analyzed in each experiment.
However, a clear advantage of single-cell approaches over bulk assays is that
adhesive subpopulations of cells can be identiied. Most SCFS techniques
allow characterizing cell adhesion down to the single-molecule level, thereby
providing detailed insights into regulation mechanisms of adhesion receptors.
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