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[Factors influencing delayed type graft-versus-host disease after allogeneic bone marrow transplantation].

Effects of the number of transplanted bone marrow cells and splenectomy performed before the transplantation on delayed type graft-versus-host disease (GVHD) were investigated in mice. The relation between delayed type GVHD and suppressor cells was also studied. Bone marrow cells (1 x 10(5)-1 x 10(7) cells) from CBA/N mice were transplanted to lethally irradiated (10 Gy) C57BL/6 mice, and the same type of transplantation was performed in other mice that underwent splenectomy. Suppressive effects of spleen cells from chimera mouse were measured by the percentage of suppression against alloantigen specific mixed lymphocyte reaction (MLR). The survival rate decreased with the number of grafted cells. However, survival rate was high in the splenectomy group even when the number of grafted cells was small. The incidence of delayed type GVHD was 0% in the 1 x 10(7) cell transplanted group, but that was more than 50% in the 1 x 10(5) cell transplanted group. There was no significant difference in the incidence of delayed type GVHD between the splenectomy group and non-splenectomy group. Spleen cells from chimera mouse without delayed type GVHD had greater suppressive effect against MLR than those with GVHD. These results suggest that alloantigen specific suppressor cells in the spleen of chimera mice inhibit delayed type GVHD.