Intercellular contacts between erythroid precursors in the bone marrow in dyserythropoiesis

Erythroblastic Synartesis: An Auto-immune Dyserythropoiesis

Erythroblastic synartesis is a rare form of acquired dyserythropoiesis, first described by Breton-Gorius et al in 1973. This syndrome is characterized by the presence of septate-like membrane junctions and “glove finger” invaginations between erythroblasts, which are very tightly linked together. This phenomenon, responsible for ineffective erythropoiesis, leads to an isolated severe anemia with reticulocytopenia. In the following report, we describe 3 new cases of erythroblastic synartesis associated with dysimmunity and monoclonal gammapathy. In all cases, the diagnosis was suggested by characteristic morphological appearance of bone marrow smears, and further confirmed by electron microscopy. Ultrastructural examination of abnormal erythroblast clusters showed that these cells were closely approximated with characteristic intercellular membrane junctions. The pathogenesis of the dyserythropoiesis was modeled in vitro using crossed erythroblast cultures and immunoelectron microscopy: when cultured in the presence of autologous serum, the erythroblasts from the patients displayed synartesis, whereas these disappeared when cultured in normal serum. Moreover, synartesis of normal erythroblasts were induced by the patient IgG fraction. Immunogold labeling showed that the monoclonal IgG were detected in, and restricted to, the synartesis. A discrete monoclonal plasmacytosis was also found in the patient bone marrow. The adhesion receptor CD36 appeared to be concentrated in the junctions, suggesting that it might be involved in the synartesis. These experiments indicated that a monoclonal serum immunoglobulin (IgG in the present cases) directed at erythroblast membrane antigen was responsible for the erythroblast abnormalities. Specific therapy of the underlying lymphoproliferation was followed by complete remission of the anemia in these cases.

Erythroblastic Synartesis: An Auto-immune Dyserythropoiesis

Erythroblastic synartesis is a rare form of acquired dyserythropoiesis, first described by Breton-Gorius et al in 1973. This syndrome is characterized by the presence of septate-like membrane junctions and “glove finger” invaginations between erythroblasts, which are very tightly linked together. This phenomenon, responsible for ineffective erythropoiesis, leads to an isolated severe anemia with reticulocytopenia. In the following report, we describe 3 new cases of erythroblastic synartesis associated with dysimmunity and monoclonal gammapathy. In all cases, the diagnosis was suggested by characteristic morphological appearance of bone marrow smears, and further confirmed by electron microscopy. Ultrastructural examination of abnormal erythroblast clusters showed that these cells were closely approximated with characteristic intercellular membrane junctions. The pathogenesis of the dyserythropoiesis was modeled in vitro using crossed erythroblast cultures and immunoelectron microscopy: when cultured in the presence of autologous serum, the erythroblasts from the patients displayed synartesis, whereas these disappeared when cultured in normal serum. Moreover, synartesis of normal erythroblasts were induced by the patient IgG fraction. Immunogold labeling showed that the monoclonal IgG were detected in, and restricted to, the synartesis. A discrete monoclonal plasmacytosis was also found in the patient bone marrow. The adhesion receptor CD36 appeared to be concentrated in the junctions, suggesting that it might be involved in the synartesis. These experiments indicated that a monoclonal serum immunoglobulin (IgG in the present cases) directed at erythroblast membrane antigen was responsible for the erythroblast abnormalities. Specific therapy of the underlying lymphoproliferation was followed by complete remission of the anemia in these cases.

Characterization of membrane homing receptors in two cloned murine hemopoietic progenitor cell lines

To characterize homing receptors that are responsible for the recognition and specific binding of hemopoietic progenitor cells to the stroma, we synthesized and 125I-labeled a number of neoglycoproteins. We used these neoglycoproteins as ligand to detect receptors on the membrane of two cloned murine hemopoietic progenitor cell lines, B6SUT and FDCP-1. Both cell lines demonstrated membrane receptors with galactosyl and mannosyl, but not fucosyl, specificities. B6SUT galactosyl receptors showed a single receptor population with a Kd of about 2.3 X 10(-7) M and 10(6) receptors per cell. Mannosyl receptors demonstrated two components with high and low affinities respectively with Kd of about 2.5 X 10(-8) M and 1.0 X 10(-7) M, and respectively about 7.4 X 10(5) and 3.7 X 10(5) receptors per cell. Comparable data were also obtained for FDCP-1. Displacement experiments indicated that radioactive ligands bound to receptors could be increasingly displaced by homologous cold ligand giving typical sigmoid-shaped curves. Cold mannosyl probe could also displace radioactive galactosyl probe in a similar manner, but cold galactosyl probe displaced radioactive mannosyl ligand with a curve demonstrating two phases, further suggesting two receptor components for the mannosyl ligand. Mature murine neutrophils and red cells as well as human neutrophils, monocytes, and red cells showed no receptors. The functional significance of these receptors in binding to stromal cells was demonstrated by quantitation of the binding of 51Cr-labeled progenitor cells to the cloned stromal cell line, D2X, before and after enzymatic removal of various carbohydrate residues of membrane glycoconjugates. Enzymatic removal of galactosyl and mannosyl, but not fucosyl, residues almost totally eliminated the binding. The findings strongly suggest that these homing receptors are present on the surface of early hemopoietic progenitor cells. With maturation the cells lose their receptors, so that mature cells can be released into the blood stream.

Red cell membrane abnormalities in two cases with a special type of a hereditary megaloblastoid hemolytic anemia

Case reports are presented of two related patients suffering from a hereditary megaloblastoid hemolytic anemia which at the moment cannot be categorized into one of the well-known entities. The main characteristics of the disease consisted of constant jaundice, macrocytic normochromic anemia, marked hemolysis without a substantial decrease in osmotic resistance, increased iron turnover and hepatic hemosiderosis at a relatively young age. One patient had to undergo splenectomy due to hemolytic crises, the other one cholecystectomy due to gallstones. In contrast to their uncharacteristic morphology in smear, red cells displayed highly variable forms ("lumpy", "Y", "U", drumstick forms) when examined in transmission and scanning electron microscopes. These changes corresponded well with reduced filtrability and aggregability of erythrocytes. The apparent relative blood viscosity was unchanged. The protein pattern of ghosts in SDS gel-electrophoresis revealed neither defects nor additional bands. Changes in the lipid composition of the membrane were indirectly deduced from electron spin-resonance studies, which showed an additional signal at g = 2.192. Similarly, the lipid related membrane mobility agent A2C failed to exert the usual stabilizing effect against osmotic stress. The negative surface potential, estimated by free flow electrophoresis, was only altered in the splenectomized patient. It is concluded that the primary abnormal physical properties of the enlarged red cell contribute at least in part to the marked hemolysis. The similar findings in the two related patients and the fact that the disorder was obviously congenital suggest a special subtype of a megaloblastoid hemolytic anemia.

Transient dyserythropoiesis in repopulated human bone marrow following transplantation: an ultrastructural study

Transmission electron microscopy was used to examine marrow samples from 15 patients with aplastic anaemia or acute leukaemia who had been treated with bone marrow transplantation. There were 11 allogeneic, three syngeneic and one autologous graft. The purpose was to estimate the frequency, type and extent of dyserythropoietic change. Transient dyserythropoietic features were substantiated in all cases. Nuclear changes were present in 12 cases, iron laden mitochondria (sideroachrestic phenomena) in 10 and cytoplasmic contacts and/or connections between red cell precursors in 10. Dyserythropoiesis was most conspicuous in the majority of cases between 14 and 28 d after transplantation but it may persist for over 100 d. No deficit in red cell production was noted and it is proposed that dyserythropoiesis in this circumstance is a physiological rather than a pathological phenomenon.

Quantitative assessment of erythropoiesis in haemolytic disease

Erythrokinetic parameters were estimated in 21 patients suffering from haemolytic disease using a mathematical model of iron kinetics. A proper definition of radioiron reflux from red cells to the plasma proved to be essential for an accurate estimate of effective and ineffective erythropoiesis in severe haemolytic conditions. Erythropoietic activity was increased in all the patients, with the marrow capable of sustaining erythropoiesis at about 6 times normal in hereditary spherocytosis and 3 times normal in autoimmune haemolytic anaemia. This proliferative effort was countered by an increase in ineffective erythropoiesis which was especially marked in hereditary spherocytosis.

Junctional structures in haemopoiesis: a study of bone marrow using freeze-fracture and lanthanum impregnation techniques

Intercellular regions of contact in the haemopoietic compartment of normal rat bone marrow were studied using freeze-fracture and lanthanum tracer techniques. Small adhering junctions (like desmosomes and their variants) were found between haemopoietic and stromal cells but tight, gap or septate junctions could not be identified. These findings are in agreement with the concept that extensive junctional structures may be inconsistent with orderly development of this transient cell system, preventing the delivery of mature cells into the circulation and resulting in ineffective haemopoiesis. Occasionally 'pinching off' of a portion of the cytoplasm of erythroid cells by stromal cells was seen, providing a means for intercellular communication. Structures similar to intercellular bridges responsible for direct intercellular communication were also seen.

Cell junctions in dyserythropoiesis

Erythroid cell junctions have previously been reported in some cases of dyserythropoietic anaemia. This study has demonstrated that they are a relatively common occurrence in dyserythropoiesis. They range from apposition of cellular membranes with preservation of the intercellular space, to membrane confluence, to interdigitation and septate-like junctions. By special staining with colloidal lanthanum, ruthenium red and tannic acid, together with studies of the effect of proteolytic enzymes, their structural composition has been identified and it was confirmed that they are not artefact. The role of cell junctions in dyserythropoiesis is discussed.

An electron microscope study of the intercellular contacts between the erythroblasts of patients with hypersiderotic bone marrows

When stained and unstained sections of hypersiderotic marrow fragments are examined in the electron microscope, some of the ferritin molecules present between a variable proportion of the erythroblasts are found to be aligned more or less transversely. These linearly arranged ferritin molecules are particularly evident in regions in which the opposing cell membranes have been sectioned obliquely and may be confused with the septa-containing intercellular junctions characteristically present between some types of invertebrate epithelial cells.