Separation of Spleen Cells in Iso-Osmotic Ficoll Density Gradients.

Osmotic pressures of polymer solutions were examined as a function of density by equilibrium dialysis, and it was reaffirmed that the vant Hoff equation cannot be used to calculate the osmotic pressure of polymer solutions at concentrations greater than 5 percent. Therefore, it appears that previous methods utilizing polymer solutions for the generation of density gradients also generated hyperosmotic gradients. However, since cells maintain their integrity best in an isotonic solution, an iso-osmotic density gradient can be prepared by superimposing a reverse salt gradient on a Ficoll gradient. Using this method, the density profiles of several cell populations were determined, and observations on fractionated C57BL mouse spleen were made. Modified author abstract