Increased response of erythroid progenitors to interleukin‐3 in sickle cell anemia: CFU‐E‐like behavior of circulating erythroid progenitors in liquid culture

Abstract

Erythroid progenitors circulating in peripheral blood and their response to erythropoietin (EPO), interleukin-3 (IL3), and phytohemagglutinin-stimulated, lymphocyte-conditioned medium (PHALCM) were assessed in sickle cell anemia (SCA) patients and controls. SCA patients have significantly higher numbers of circulating burst-forming unit-erythroid (BFU-E) compared with controls (mean +/- SEM, 940.27 +/- 129.11 per ml and 86.56 +/- 19.74 per ml, respectively; P less than 0.0001). At low doses of EPO, BFU-E-derived colonies were significantly increased in SCA patients compared with controls (each P less than 0.05). The EPO dose required to produce 50% of maximum colony numbers was 47 times greater in control subjects than in SCA patients. Moreover, in 11 of 17 patients with SCA, spontaneous BFU-E-derived colonies were formed without added erythropoietin. This phenomenon was not observed in control subjects (P = 0.035). PHALCM developed from mononuclear cells of SCA patients had significantly greater stimulatory effect than did that derived from controls regardless of the source of target cells (each P less than 0.05). A two-step study of IL3 sensitivity of erythroid progenitors was conducted. First, in a liquid culture system, circulating erythroid progenitors of SCA patients and controls were incubated in the presence of varying doses of IL3. During a second step, CFU-E-like colonies were observed in methylcellulose cultures of these cells. The mean numbers of colony-forming unit-erythroid (CFU-E)-like colonies was significantly higher in SCA patients compared with control subjects at low doses of IL3 (each P less than 0.02). The increased response of erythroid progenitors to IL3 and the increased production of hemopoietic growth factors (IL3 or non-IL3) contribute to the hemopoietic response in SCA patients. These mechanisms and increased sensitivity of the BFU-E to EPO may explain lower than expected EPO levels in SCA patients.

Spontaneous erythroid colony formation in Brazilian patients with sickle cell disease

“…The only common feature in all these diseases that could explain this similarity is the increased sensitivity to Epo [4,6,10,18,20,24]. Epo hypersensitivity in SS as well as ␤ thalassemic patients has been demonstrated by several authors [4,5,8,10] using Epo dose-response curves. These findings demonstrate considerable colony formation at low Epo concentrations, when compared with control subjects.…”

“…Thus, it is possible that this Epo hypersensitivity may occur as a result of changes in the erythroid progenitors such as increased numbers of Epo receptors, increased accessibility of otherwise cryptic receptors, activation or change in the affinity of the receptors for the ligand on the surface of the progenitor cells, and/or altered Epo signal transduction pathway [5,[35][36][37][38][39]. Thus, it is possible that this Epo hypersensitivity may occur as a result of changes in the erythroid progenitors such as increased numbers of Epo receptors, increased accessibility of otherwise cryptic receptors, activation or change in the affinity of the receptors for the ligand on the surface of the progenitor cells, and/or altered Epo signal transduction pathway [5,[35][36][37][38][39].…”

“…Among these disorders are homozygosity for the Hb S gene or sickle cell anemia (SS), Hb SC disease, or double heterozygosity for the Hb S and Hb C genes, and Hb S/␤ thalassemia, in which patients are heterozygous for the Hb S and a ␤-thalassemia gene. In addition, some authors have observed the formation of spontaneous BFU-E colonies (without stimulus) in SS patients [5]. SCD patients are characterized by a chronic hemolytic anemia, erythroid hyperplasia in the bone marrow as well as reticulocytosis.…”

Spontaneous erythroid colony formation in Brazilian patients with sickle cell disease

“…They often have increased levels of Hb F, which if sufficiently high may lead to some modulation of clinical symptoms. It is well documented that SS [3][4][5][6][7] and ␤ thalassemic [6,8,9] patients have a higher than normal number of circulating BFU-E. It was demonstrated further that these progenitors expressed hypersensitivity to erythropoietin (Epo) [4,8,10].…”

“…It was demonstrated further that these progenitors expressed hypersensitivity to erythropoietin (Epo) [4,8,10]. In addition, some authors have observed the formation of spontaneous BFU-E colonies (without stimulus) in SS patients [5]. This finding is of particular interest because spontaneous BFU-E colony formation (autoproliferation) is generally thought to be a characteristic feature of myeloproliferative disorders such as polycythemia vera, which is associated with abnormal expansion of erythroid stem cell clones.…”