The problem of toxicity in the bioassay for erythropoietin using mouse fetal liver cells

The use of neonatal instead of fetal calf serum, as a constituent of the culture medium, confronted the authors with the problem of toxicity in the fetal liver cell erythropoietin assay. Tested human sera were toxic at rather low concentrations. Heating the human sera for 30 min at 56 degrees C abolished the toxicity. Heating the Step I or Step III sheep plasma erythropoietin had very little influence. Fetal calf serum proved to be more suitable than neonatal calf serum for two reasons: The toxicity of human sera was less pronounced when fetal calf serum was used in the medium, and it gave a wider separation of unstimulated and maximally stimulated cultures.