Splenopentin (DAc-SP-5) accelerates the restoration of myelopoietic and immune systems after sublethal radiation in mice

Abstract In 1981 a new splenic hormone was described by Audhya et al. ( Biochemistry , 20 , 6195–6200, 1981). At first designated as thymopoietin III, the complete amino acid sequence had been described as splenin in 1984. For the pentapeptide corresponding to amino acids 32–36 of splenin was shown to be active in immunological systems. The synthetic pentapeptide splenopentin (DAc-SP-5) and the sequence 32–36 of splenin are identical. In this study the recovery of immunocompetence in mice following sublethal irradiation is shown to be enhanced by DAc-SP-5. The treatment effects of DAc-SP-5 were verified by splenic plaque-forming response to a T-cell dependent antigen and in the hematopoietic colony-forming assay. These effects were associated with an accelerated recovery of leukocyte counts in peripheral blood and spleen without significant changes in the relation between leukocyte and lymphocyte subpopulations. Furthermore, in comparison to control animals DAc-SP-5 treated mice showed in the first weeks postexposure a significantly higher number of bone marrow derived cells as well as granulocyte — macrophage and macrophage colony-forming cells (GM-CFC and M-CFC). Therefore, DAc-SP-5 may be a useful substance for treating secondary forms of bone marrow depression.