The measurement of cell adhesiveness by an absolute method

The development of a quantitative method for measuring cell adhesion would allow tests to be made of a variety of hypotheses concerning the role of cell adhesiveness in many morphogenetic processes, such as segregation (Steinberg, 1963; Curtis, 1960, 1967), contact inhibition of movement (Abercrombie, 1961), malignancy, etc. Furthermore, the development of a quantitative method giving absolute measurements of cell adhesiveness would be of considerable value in that it would allow critical experiments to be made to test hypotheses about the mechanism of cell adhesion. Basically, two methods exist for the measurement of cellular adhesiveness: (i) a measure of the force or energy required to reseparate two cells or a group of cells from one another or from a non-cellular substrate; (ii) a measure of the forces or energies of interaction involved in bringing two cells or cell groups into adhesion. The first method was introduced as a qualitative test of adhesiveness by Dan (1936). Recently, Brooks, Millar, Seaman & Vassar (1967) have made ingenious calculations of the probable magnitude of the adhesive energies which have to be overcome in dispersing a tissue by mechanical means into single cells. Measurement of the forces that have to be used to disperse the tissue can be used to derive a value of the adhesiveness of the cells as Brooks et al. (1967) have done. But there are difficulties in this method since intercellular materials, such as collagen, may contribute to the average resistance of a tissue to dispersion by mechanical forces, and if the hypothesis advanced by Weiss (1961) is correct, the measurement is not of the adhesiveness of cells but of the mechanical resistance of the cells to being broken. With the first of these considerations chiefly in mind, it seemed desirable to develop a method for measurement of adhesiveness using the formation of adhesions between cells.