Cesare Peschle

Pure Red Cell Aplasia: Studies on an IgG Serum Inhibitor Neutralizing Erythropoietin

Summary. A new type of IgG serum inhibitor in adult pure red cell aplasia (PRCA) has been investigated. This inhibitor is directed against circulating erythropoietin (Ep) (PRCA type B), rather than the erythroid marrow (PRCA type A). Thus, the IgG inhibitor, after interaction with Ep in solution, is precipitated together with Ep by addition of goat anti‐human gamma‐globulins. Pre‐therapy PRCA serum, although apparently devoid of Ep, shows considerable Ep activity following acidification and boiling. The inhibitor is absent from post‐therapy serum, while Ep levels are elevated. An experimental model for PRCA type B has been established in normal mice after prolonged administration of pre‐remission serum IgG.

Kinetics of Erythroid and Myeloid Stem Cells in Post-Hypoxia Polycythaemia

Summary. The number of erythroid burst‐ (BFU‐E) and colony‐forming units (CFU‐E), as well as of myeloid‐macrophage colony‐forming units (CFU‐C), has been evaluated in tibial marrow and spleen of ex‐hypoxic polycythaemic mice, at sequential time intervals after the end of hypoxia.

INTERACTIONS OF INTERFERON WITH IN VITRO MODEL SYSTEMS INVOLVED IN HEMATOPOIETIC CELL DIFFERENTIATION

Erythropoiesis has been a suitable tool for defining several aspects of the regulation of eukaryotic cell differentiation. The control of red blood cell formation involves a number of critical steps, which include proliferation of pluripotent hemopoietic stem cells, their commitment to erythopoiesis, the proliferation of committed precursor cells, and, finally, the expression of several biosynthetic and morphogenetic activities characteristic of terminally differentiated erythroid cells.,2 The in vitro development of clonal short-term cell cultures in semi-solid medium permitted identification of the precursors at different stages of the erythroid pathway. The most immature, pluripotent hemopoietic stem cell is the so-called CFU-S (spleen colony-forming unit),3 which is capable of both selfrenewal and differentiation to various precursors of the erythroid myelomonocytic, megakaryocytic and lymphoid lineage^..^ Two erythroid progenitors have been identified in mammals, the erythroid burst(BFU-E) and colony(CFU-E) forming-unit: the former represents an early progenitor, which differentiates into the late one, i.e. CFU-E. This schematic classification includes precursors at several stages of differentiation, which sequentially evolve one into the other, in a process regulated via both longand short-range mediators?lo These include hormones such as erythropoietin and microenvironmental influences, respectively.

Erythropoietin production by the liver in fetal-neonatal life

Abstract Subtotal ablation of the liver in 10-day-old ( i.e. , neonate) rats resulted in almost complete abolition of the erythropoietin (Ep) response to a 6-hr bout of hypoxia, starting 1 hr after the operation. Partial or subtotal liver regeneration on day 2 or 3 post-hepatectomy was correlated respectively with partial or subtotal restoration of Ep production. Ablation of the spleen or kidneys in 7- or 10-day-old rats did not modify hypoxic Ep levels. It is concluded that the liver is the main or exclusive source of Ep in the neonate rat, and possibly represents the main site of hormonal production in fetal-neonatal life of mammals.

Hepatic Erythropoietin: Enhanced Production in Anephric Rats with Hyperplasia of Kupffer Cells

Erythropoietin (Ep) levels were assayed in serum of adult male rats subjected sequentially to (1) administration of colloidal carbon, Zymosan or their vehicles (2) sham operation or bilateral nephrectomy with and without subtotal hepatictomy, and (3) hypoxia (0.45-0.40 atmospheres of air for 6 h starting 1 h after the operation). In anephric rats these agents induced a significant potentiation of hypoxic Ep activity. Since they did not apparently modify the kinetics of exogenous Ep, it is postulated that this phenomenon is mediated by enhanced extrarenal Ep production. Both colloidal carbon and Zymosan induced hyperplasia of the reticuloendothelial system (RES). Moreover, subtotal hepatectomy almost abolished the Ep response to hypoxia evoked by Zymosan. The correlation between hyperplasia of hepatic RES and enhanced Ep production in anephric rats primed with these agents suggests that Kupffer cells constitute a major source for extrarenal Ep. Additionally, it is of interest that colloidal carbon and Zymosan did not significantly modify the renal production of Ep.

Enhanced erythroid burst formation in mice after testosterone treatment

Abstract A single administration of testosterone propionate (TP) in ex-hypoxic polycythemic mice induces, at 24 hr after androgen, an amplification of the erythroid burst-forming unit (BFU-E or B) pool in marrow. This phenomenon is not associated with an amplification of the erythroid colony-forming unit (CFU-E or E) compartment and is followed by its depletion. In the other hand, the 36–49 hr rise of erythropoietin (Ep) levels in serum is followed by a 60-hr amplification of the E pool. It is suggested that the latter phenomenon is mediated by enhanced Ep production, whereas the early amplification of the B compartment may derive from a direct influence of TP at the stem cell level.

Renal Mechanisms Underlying Cyclic AMP Action on Erythropoiesis

Summary. Dibutyryl cyclic AMP (dbc‐AMP) was injected into ex‐hypoxic polycythaemic mice either alone or with anti‐erythropoietin (anti‐Ep) serum. Anti‐Ep totally abolishes the wave of erythropoiesis evoked by dbc‐AMP. These results might indicate either that the action of this agent is totally Ep‐dependent, or that a residual amount of endogenous Ep is necessary to allow dbc‐AMP to exert a direct effect at the marrow level. The latter mechanism, however, is precluded by experiments indicating that administration of moderate amounts of anti‐Ep, although abolishing totally the erythroid response to dbc‐AMP, do not induce complete suppression of endogenous Ep activity and erythropoiesis. Furthermore, a significant rise of Ep plasma levels is observed in rats receiving dbc‐AMP. Since this agent does not apparently modify the kinetics of endogenous Ep, it is postulated that dbc‐AMP induces a rise in Ep production. This phenomenon, although unmodified in ureter‐ligated animals, is completely abolished by bilateral nephrectomy. It is therefore concluded that dbc‐AMP induces in vivo a stimulatory effect on erythropoiesis via increased production of Ep, via a renal mechanism possibly represented by elevated levels of the renal erythropoietic factor.

Erythroid colony formation and erythropoietin activity in mice treated with estradiol benzoate.

Abstract In mice administered with estradiol benzoate (EB) at 0.2 or 5 μg dose levels, the number of erythroid colony-forming units (CFU-E) in marrow declines progressively starting from 12 through 48 hr. On the other hand hypoxic erythropoietin (Ep) production, although potentiated in animals primed with relatively large dosages of EB (5–25 μg), is significantly diminished after treatment with lower amounts of estrogen (0.2 μg). In mice primed with large amounts of EB, the enhancement of Ep activity apparently compensates the depleting influence on marrow CFU-E, thus leading to a nearnormal erythroid response to hypoxia. On the other hand, a sharp drop of this parameter is observed in animals primed with the lower dosage (0.2 μg), i.e. the depleting influence on the CFU-E pool is not compensated here by potentiation of the Ep response.

Regulation of Erythropoiesis and its Defects

A concise review of recent advances in studies of mechanisms controlling the rate of erythropoiesis, including some original results, is presented. The first and second sections are focused on erythropoietin (Ep) and the erythroid stem cell respectively. In the third one, clinical conditions caused by a defect in the regulation of erythropoiesis are discussed.

Testosterone action on BFU-E and CFU-E: Correlation between enhancement of proliferative rate and amplification of pool size

Abstract As previously reported, a single administration of testosterone propionate (TP) in ex-hypoxic polycythemic mice induces an 18–24 hr amplification of the erythroid burst-forming unit (BFU-E) pool and a 60-hr expansion of the erythroid colony-forming unit (CFU-E) compartment. Both phenomena are here shown to be temporally associated with an increase of the in vitro 3H-TdR sensitivity of these compartments, thus indicating an elevation of their proliferative rate. On the other hand, no significant modification of both the DNA synthesis index and the pool size of BFU-E and CFU-E were observed at respectively 60 or 18 hr. At either time interval, both 3H-TdR sensitivity and compartment size were not modified at the level of the myeloid-macrophage colony-forming unit (CFU-C). It is therefore suggested that the early and late expansion of respectively BFU-E and CFU-E number after TP injection is at least partially mediated by enhancement of the proliferative rate within the respective compartments. Finally, mechanisms underlying TP action on BFU-E and CFU-E pools are discussed in the light of both present and previous observations.