Prevention of graft-versus-host mortality in mice by preincubation of the graft with highly purified spleen-derived immunosuppressive peptides.

Two non-species-specific spleen-derived immunosuppressive peptides (SDIP) have been highly purified from bovine spleen and are referred to as SDIPe and SDIPHP with reference to the last step of the purification procedure (electrophoresis or high pressure liquid chromatography, respectively). Preincubation of lymphoid cells with very dilute preparations of both SDIPs significantly reduced their capacity to induce a lethal graft-versus-host reaction (GVHR), but did not diminish their capacity to form hematopoietic colonies in the spleens of lethally irradiated syngeneic hosts (CFUs). Therefore, such pretreatment of bone marrow grafts by SDIP could be useful candidate for GVHR prevention. In contrast, preincubation with thymulin (serum thymic factor (FTS) plus ZnCl2), which shares several physicochemical properties with SDIP, significantly improved the ability of lymphoid cells to induce lethal GVHR. The opposite immunomodulatory effects of these highly similar peptides are discussed.