Effect of a streptococcal preparation, OK-432, on hematopoietic spleen colony formation in irradiated mice.

In vivo effect of an immunostimulant, OK-432, on hematopoietic spleen colonies (CFU-S) was investigated in irradiated JCL/ICR mice. Administration of OK-432 i.p. at various times before and/or after irradiation resulted in a significant increase in endogenous CFU-S. This increase was further characterized microscopically by an increase in the number of megakaryocytic colonies. Transplantable exogenous CFU-S also increased when normal bone marrow cells were transplanted into irradiated recipient mice previously given OK-432 i.p. Treatment with OK-432 gave rise to an earlier recovery of granulocyte and, particularly, platelet counts in the peripheral blood after irradiation. All these findings indicate that an increase in CFU-S is associated with activated hematopoietic microenvironment by OK-432.