Biology Reference
In-Depth Information
23
Cell Adhesion Assays
Martin J. Humphries
1. Introduction
This chapter will outline in detail the two standard assays used in the author's
laboratory for quantitating the adhesion of cells to an immobilized substrate.
The attachment assay, which employs a colorimetric detection of bound cells,
is based on Kueng et al.
(1)
, and the spreading assay, which employs phase
contrast microscopy to measure the flattening of adherent cells, is based on the
method of Yamada and Kennedy
(2)
.
It is important to realize that cell adhesion is a complex process that involves
many different molecular interactions, including receptor-ligand binding,
changes in the fluxes through intracellular signaling pathways, and modulation
of cytoskeletal assembly. Consequently, adhesion assays not only measure the
contacts between a cell and extracellular adhesion proteins, but also provide
information about other cellular events. For this reason, care needs to be taken
before choosing to perform adhesion assays. The most common uses of adhe-
sion assays are a) to test the ability of a specific type of cell or cell line to
adhere to a specific adhesive substrate, and b) to test the sensitivity of a spe-
cific cell-substrate interaction to inhibitors, but it is also apparent that adhesion
assays can be used to probe the contribution of other cellular processes.
A number of factors will affect the decision whether to use a cell-spreading
assay or a cell-attachment assay. Spreading assays take longer to perform,
but are less prone to nonspecificity. For example, many molecules can mediate
attachment of cells in a nonphysiological manner, but very few of these mol-
ecules are able to mediate spreading. In addition, information can be gained
about the ways in which the cells respond to the substrate by observing cells in
a spreading assay. For example, the morphology of cells can differ on different
substrates even if the level of spreading is the same, and now that our under-
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