HOST F1-MICE PRETREATED WITH GRANULOCYTE-COLONY-STIMULATING FACTOR ACCEPT PARENTAL BONE-MARROW GRAFTS IN HYBRID RESISTANCE SYSTEM

In the setting of hybrid resistance, parental C57BL/6 bone marrow (BM) grafts are vigorously rejected by lethally irradiated (C57BL/6xDBA/2) F1 mice. However, F1 mice pretreated by continuous administration of granulocyte colony-stimulating factor (G-CSF) with a miniosmotic pump before BM grafting developed day-8 splenic colonies of donor origin. T his inhibitory effect on rejection was reversible because F1 mice rega ined the capacity to reject parental BM when the pump ceased functioni ng. The appearance of only a small number of colonies with the adminis tration of G-CSF soon after BM grafting suggested the importance in pr oducing this inhibitory effect of pre-exposure of host mice to G-CSF. Because G-CSF administration with a syngeneic combination did not infl uence the number of colonies, an altered distribution of grafted precu rsors was unlikely. The absence of a reduction in the number of NK1.1- positive cells in G-CSF-treated mice suggested functional impairment o f natural killer cells, major effecters in hybrid resistance, but furt her study is necessary to elucidate the mechanism underlying this phen omenon. However, our results indicate the importance of G-CSF as a reg ulator in a certain type of immune response and raise the possibility of clinical application in transplantation medicine. (C) 1997 by The A merican Society of Hematology.