In vivo production and hematopoietic activity of interleukin 3 (IL-3) in mice

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We have demonstrated a high level of interleukin 3(IL-3) in the serum of mice with graft-versus-host disease(GVH-D).The level of IL-3 rised as the GVH-D became severer.The level of this factor was measured by the method of either erythroid colony-formation from 14 day-fetal mouse liver cells or^3H-TdR uptake in FDC-P2 cells which are IL-3 dependent cell line.The inhibitory activity was detected in the serum by the method using FDC-P2 cells but not erythroid colony-forming technique.However,the specificity or physiological role of this activity was obscure.The possibility that the hematopoietic activity of the serum might be due to a factor induced by endotoxin was excluded by the experiments with endotoxin non-responder C3H/Hej mice,in which the activity was elevated as much as the control mice when suffering from GVH-D.The production of IL-3 was observed in liquid culture media from bone marrow,spleen and lymph node cells in GVH-D mice.The in vivo effect of IL-3 was confirmed in mice injected with the serum from polycytemic GVH-D mice, in which serum erythropoietin level was reduced into undetectable range.Total numbers of BFU-E,CFU-C and CFU-Mix were remarkably increased in spleens of the mice 3 days after the injection.IL-3 in the serum stimulated the proliferation and differentiation of the hematopoietic progenitors in mice. Consequently,it plays and important role in hematopoiseis in vivo as well as in vitro.