Prolongation of graft survival in ALS-treated mice by donor-specific bone marrow. Density gradient fractionation of the active bone marrow cells.

Antilymphocyte serum (ALS)-treated recipient mice that are infused with donor bone marrow cells have been shown to enjoy prolonged skin graft survival. In the present experiments, discontinuous density gradient centrifugation in Percoll was used to prepare fractions of these cells. Two of four fractions had good graft-prolonging ability. In experiments in which the density of the gradients was varied, we were able to estimate the density of a major portion of the cells active in graft prolongation as being in a range of 1.061 to 1.066 g/ml, and to produce one fraction with superior graft-prolonging activity. This fraction constituted only 10% of the recovered cells, was enriched for small-to-medium lymphocytes, Ia+, Thy-1+, and IgM+ cells, and contained cells bearing a marker known to be present on active cells, Fc gamma R. Additionally, this fraction contained cells capable of suppressing the mixed lymphocyte reaction, although two denser fractions, of poor-to-good graft-prolonging ability, also shared this ability. The effectiveness of this method in bringing about a high-capacity, rapid isolation of cells that can augment graft survival in immunosuppressed recipients makes it well suited for future clinical application.