Elevation of erythroid colony-stimulating activity in the serum of mice with graft-versus-host disease

Serum obtained from (C3H X C57BL) F1 hybrid mice injected with parental (C57BL) lymph node cells after 600 rad irradiation contained a high level of an erythropoietic factor, which enhanced erythroid colony formation by fetal C57BL liver cells in methylcellulose cultures. The serum level of this erythroid colony-stimulating activity increased as the dose of lymph node cells injected increased and as suppression of endogenous spleen colonies (indicative of GVH severity) became more marked. Erythropoietin was also elevated in the sera of these mice. When these animals were transfused with washed packed red cells to induce plethora after sublethal irradiation and injection of lymph node cells, the erythropoietin level decreased, but erythroid colony-stimulating activity remained elevated. On the other hand, in anemic mice treated with phenylhydrazine, this erythropoietic factor was not detected, although the serum level of erythropoietin was elevated. These results suggest that a graft-versus-host (GVH) reaction may induce the production of an erythropoietic factor other than erythropoietin and that anemia itself may not be a stimulus for its in vivo production.