Cell-cell affinity probed by countercurrent distribution in two-polymer aqueous phase systems

Abstract

Aqueous solutions of dextran and of polyethylene glycol when mixed form immiscible liquid two-phase systems with a polyethylene glycol-rich top and a dextran-rich bottom. Such phases can be buffered and rendered isotonic and are suitable for the partition of cells. The partition coefficient of cells (i.e., their relative affinity for the top or bottom phase or their adsorption at the interface) depends on the polymer concentrations, on the ionic composition and concentration and, most sensitively, on their membrane surface properties. When two cell populations are mixed the partition coefficient of each is unaffected by the presence of the other population unless an interaction takes place between them. By countercurrent distribution of two cell populations, in a phase system selected such that the partition coefficient of one population is high (i.e., more cells in the top phase) and of the other low, one should be able to detect subtle interactions between cells in the two populations should they occur. Results of experiments with a model system consisting of human peripheral blood mononuclear cells and sheep red blood cells bear out the feasibility of this approach. At low ratios of sheep erythrocytes to mononuclear cells no interaction is apparent. With increasing ratios there is an increasing shift in the distribution curve of subpopulations of mononuclear cells (i.e., T-lymphocytes) as they interact with the sheep red cells. Substitution of rabbit red cells for sheep erythrocytes (at high ratios) reveals a small yet significant shift of a subpopulation of mononuclear cells as well. Distribution of human peripheral blood lymphocytes from patients with chronic lymphocytic leukemia (all B-lymphocytes) are essentially unaffected by the presence of sheep red cells. This sensitive new method, still in its infancy, holds out the hope for the detection of previously unknown cell-cell affinities and for probing suspected cell-cell interactions.