Influence of human serum components on measurement of erythropoietin biological activity in vitro. Studies with a rabbit bone marrow bioassay procedure.

Abstract

The influence of human serum components during in vitro determination of erythropoietin biological activity has been examined in a modified in vitro bioassay procedure utilising rabbit bone marrow as the erythropoietin-responsive tissue. The number of erythroblasts present after 5 d in suspension culture provided a measure of erythropoietin biological activity with a degree of sensitivity equivalent to that provided by estimation of 59Fe incorporation into haem, but possessed the advantage of lacking the susceptibility of the latter method to the level of human serum transferrin saturation. Erythropoietic stimulation was blocked by 10% human serum unless all sera incorporated into the bioassay was previously heated at 56 degrees C. Human serum under the latter conditions was shown to contain material which stimulated erythropoiesis, but which differed in its mode of action from erythropoietin in that it operated by amplifying the response to erythropoietin. Correction for these effects substantially altered interpretation of erythropoietic stimulatory activity of human serum to yield values in keeping with those reported for in vivo bioassay. These findings illustrate the need to clarify the role of human serum components which modify the action of erythropoietin under culture conditions, in view of their potential contribution to discrepancies between values obtained by different bioassay procedures.