A Rapid Method for the Separation of Functional Lymphoid Cell Populations of Human and Animal Origin on PVP‐Silica (Percoll) Density Gradients

Subclasses of lymphocytes can be separated on gradients of non‐toxic polyvinylpyrrolidone‐coated colloidal silica (Percoll) by virtue of differential densities. Such gradients can yield functionally active lymphocyte populations after brief centrifugation. Gradients can he generated in a discontinuous step fashion and centrifuged in standard table‐top laboratory centrifuges or as self‐generating gradients duriny ultracentrifugation. The density medium has low viscosity and can be made isotonic for virtually any use. Gradients have proved useful in both human and experimental animal studies, and high percentage yields allow for separations from small cell numbers. Methods are described for separation of whole blood and lymphotd subpopulations. including blasts stimulated with mitogens or in mixed lymphocyte reactions. The cytotoxic capability of various density fractions was evaluated for mixed lymphocyte culture‐induced allogeneic killing and spontaneous, so‐called ‘natural’ killer cell activity. The lower density associated with blast transformation allows for significant enrichments of stimulated cells from in vitro cultures. Higher thymidine incorporation, restimulation in mixed lymphocyte reactions, and greater cytotoxic capacity are associated with these‘blast’fractions.