Some Properties of Serum Obtained from Rabbits Immunized with Human Urinary Erythropoietin

Abstract Sera obtained from rabbits after immunization with human urinary ESF can neutralize the biological activity of human urinary, sheep, rat, and rabbit plasma ESF. Such sera can depress erythropoiesis in normal mice. The neutralizing ability of such sera is found in the γ-globulins. The finding that absorptions of the immune sera with a wide variety of proteins did not alter the neutralizing ability suggests that considerable immunologic specificity is involved in the neutralization reaction. This suggestion is further supported by the finding that immune sera against a variety of proteins do not effect the erythropoietic response elicited by the injection of exogenous erythropoietin. The injection or addition of antisera against proteins or protein hormones known to be of importance in normal erythropoiesis has little or no effect on the ability of exogenous ESF to stimulate erythropoiesis in polycythemic mice. One exception is anti-ovine thyrotropin, which significantly decreased the erythropoietic response seen in polycythemic mice after the injection of sheep ESF. The finding that mild acid hydrolysis destroyed the biological activity of human urinary ESF and altered antigenic determinants on the ESF molecule suggests that the groups necessary for biological activity may be specific antigenic determinants. These properties of the immune sera are consistent with the concept, which we previously proposed, that the neutralization of the biological activity of ESF by anti-ESF is the result of an immunologic reaction. The availability of such immune sera offers a potent tool for investigating many of the current problems on the role of ESF in the regulation of erythropoiesis.