The ultrastructure of dyserythropoiesis in aplastic anaemia

Serial morphologic observation of bone marrow in aplastic anemia in children

Recent reports of myelodysplastic syndrome/acute myeloid leukemia (t-MDS/AML) developing after treatment with immunosuppressants and granulocyte colony-stimulating factor (G-CSF) has raised the question of whether previously unrecognized myelodysplastic features had been present or whether actual transformation had occurred. We undertook a multi-institutional study of 112 children with aplastic anemia diagnosed between 1976 and 1996 and then treated with immunosuppressants with or without G-CSF. In each case, bone marrow specimens were tested at study entry and every 6 months for 3 years to detect t-MDS/AML as defined by morphologic and molecular/cytogenetic criteria. As of December 2001, all eligible patients had been followed for a median of 3 years. Morphologic abnormalities were found in 17 cases. The patients in 4 of these cases had clonal cytogenetic abnormalities and received MDS diagnoses. The morphologic features of the patients with and without clonal cytogenetic abnormalities were indistinguishable. However, the mast cell content was lower in cases with cytogenetic abnormalities than in cases without them. An elucidation of the role of mast cells may provide information about the differences between aplastic anemia and MDS or about the transition of aplastic anemia to MDS.

The congenital dyserythropoietic anaemias

Congenital dyserythropoietic anaemias (CDA) are a category of rare genetic diseases that affect erythropoiesis. Dyserythropoiesis is associated with abnormal erythroblasts and leads to altered red cells, the amount of which is insufficient. There are three main, well-defined CDAs, CDA I, II and III. Their characterization is based on a careful examination of the bone marrow under light and electron microscopes. In addition, a number of rare or unique forms of dyserythropoiesis have been reported. At least with respect to CDA I to III, the clinical evaluation is reaching an ever increasing refinement: age of discovery, determinants of iron overload and/or biliary complications. Over the past few years, a more promising breakthrough has been the localization of the genes responsible for CDA I, II and III, that is, 15q15.1-q15.3, 20q11.2 and 15q21-q25, respectively. Epidemiological studies have now become possible. The identification of the genes is pending.

Ultrastructural abnormalities of bone marrow erythroblasts in refractory anemia

Ultrastructural abnormalities of erythroblasts in 30 patients with refractory anemia (RA) according to FAB classification were studied. Nuclear clefts, iron-laden mitochondria, and myelin figures in cytoplasm were most frequently observed. Eleven patients (36.7%) with nuclear clefts of erythroblasts had a higher platelet count and higher incidence of cytogenetic abnormalities linked to poor prognosis than the patients without nuclear clefts. They also had a higher frequency of leukemic transformation and shorter survival than the patients without nuclear clefts. The nuclear clefts of erythroblasts, which are the result of impairment of DNA metabolism or nuclear formation and fusion during mitosis, may be one of the adverse prognostic factors for patients with RA.

A role for mitochondrial DNA in the pathogenesis of radiation-induced myelodysplasia and secondary leukemia

The onset of acute myeloid leukemia following ionizing radiation or alkylating agent exposure is antedated months to years by the development of 'preleukemia', or secondary myelodysplastic syndrome (sMDS). Mitochondrial abnormalities induced by chloramphenicol and clonal deletions of mitochondrial DNA (mt DNA) in the bone marrow create hematological defects similar to sMDS, and abnormal dimers of mt DNA are observed in acute leukemia. This suggests a role for mt DNA in the pathogenesis of sMDS and secondary leukemia. We outline disparate experimental evidence to support this concept and suggest a role for select protease inhibitors in the clinical management of this disorder.

Congenital dyserythropoietic anaemia type II (HEMPAS): characterization of aberrant intracellular organelles by immunogold electron microscopy

Erythrocytes are reticulocytes obtained from peripheral blood of a congenital dyserythropoietic anaemia type II patient were examined by immunoelectron microscopy using anti-band 3 and anti-glycophorin A antibodies. Vacuoles which have membranous structures inside were stained heavily by these antibodies, indicating the presence of band 3 and glycophorin A in these vacuoles. Empty vacuoles which open to the cell surface and those present in cytoplasm were also stained by these antibodies at the inside of the wall. These observations suggest that the vacuoles are functioning for trapping and discarding the defective plasma membranes. On the other hand, small vesicles and ferritin-loaded vacuoles were not stained by these antibodies. In these experiments, peripheral cisternae and most of the intracellular membranous structures at blebs and clefts were not stained by the antibodies. Therefore, they are probably part of the endoplasmic reticulum or are derived from intracellular organelles but not from the plasma membranes.

Subsets of patients with aplastic anemia identified by flow microfluorometry

We used flow microfluorometry to analyze peripheral-blood mononuclear cells from 50 patients with aplastic anemia, to determine whether patients who would recover after immunosuppressive therapy could be distinguished before treatment from those who would not recover. Cells were labeled with murine monoclonal antibodies that are relatively specific for B cells, T cells, T-cell subsets, and monocytes. The data suggested that the number of lymphocytes and the ratios of various subclasses of T cells were not useful in identifying patients who were likely to recover. The complete absence of monocytes was found to identify patients who would not recover, but the presence of monocytes was also sometimes associated with lack of recovery. An unexpected finding was the significant (P less than 0.0001) association between clinical recovery and the presence of a population of small cells (4 to 8 micron) that were phenotypically associated with the erythroid lineage. If this association is confirmed, flow microfluorometry may be useful in selecting the optimal treatment for individual patients with aplastic anemia.

Emperipolesis and annulate lamellae in erythroleukaemia

The bone marrow in the erythraemic phase of 2 erythroleukaemia patients was studied electron microscopically. Emperipolesis of erythrocytes as well as annulate lamellae were revealed in the cytoplasm of the erythroblasts of these cases. It is assumed that these findings show a high rate of erythroblastic proliferation. This is the first report of emperipolesis within the erythroblast by erythroleukaemia. In addition, other various abnormalities, namely, nuclear-cytoplasmic asynchrony, nuclear bleb or cleft formation, abundant glycogen particles and ferruginous micelles in mitochondria such as described in some previous reports, were also recognized.

Ultrastructural characteristics of therapy-related acute nonlymphocytic leukemia: evidence for a panmyelosis

Leukemic cells from 13 patients with therapy-related acute nonlymphocytic leukemia (ANLL) were studied by electron microscopy. All of the patients had radiotherapy, and/or alkylating agent chemotherapy for other neoplastic disease 25 to 182 months prior to the diagnosis of ANLL. All cases manifested ultrastructural evidence of a panmyelopathy. All marrow cell lines exhibited nuclear--cytoplasmic asynchrony and abnormalities of cell size. Developing granulocytes exhibited decreased primary and/or secondary granule formation and abnormal granules characterized by irregular shape, large size and internal membranous lamellae. Monocytes showed perinuclear bundles of microfilaments. In some cases, the predominant leukemic blasts showed evidence of early basophil granule development which was not appreciated in light microscopy. Abnormalities in erythroid cells included abundant intracristal mitochondrial iron, large vacuoles, infoldings of redundant membrane and membrane-bound nuclear blebs and intranuclear clefts. Megakaryocytes manifested decreased numbers of granules and demarcation membranes. Excessively large platelets with decreased or abnormal granules were identified; giant compound granules with irregular contour and variable electron density were present. Several of the changes in the developing hematopoietic cells were similar to those described in preleukemia and in certain nonneoplastic disorders. The consistent panmyelosis in therapy-related ANLL together with several uniform clinical features defines a specific clinicopathologic entity.

Hematologic and myelogenous effects of inhaled benzene in the pig and the rat

Four groups of 4 domestic pigs were exposed to 0, 20, 100, and 500 ppm benzene vapor 6 h/d, 5 d/wk, for 3 wk. Two groups of 10 rats were exposed to 0 and 500 ppm: the exposed rats for 6 h/d, 5 d/wk, for 3 wk, the nonexposed rats for 6 h/d, 5 d. Rats were killed within 72 h after exposure; values for pigs were obtained shortly after exposure and on final examination at 4-16 wk after exposure. Pigs were evaluated for changes in white and red blood cell counts, hemoglobin level, lymphocyte count, proportion of E-rosette-forming lymphocytes, myeloid-erythroid ratio, and presence of multinucleate erythroblasts. With the exception of the E-rosette test, the same parameters were measured in the rat. Statistically significant (p less than 0.05) depression of white cell counts, total lymphocytes, and proportion of E-rosette-forming lymphocytes was observed in pigs exposed to 500 ppm; recovery to values not significantly different from control values was observed on final examination. Fewer postexposure effects were seen at 100 ppm, and there were no significant differences from control values at 20 ppm. Both pigs and rats exposed to 500 ppm showed a significant decrease in the mean myeloid-erythroid ratio within 72 h. These values returned to normal in the pig 4-16 wk after exposure; recovery in the rat was not evaluated. An increased number of bone marrow erythroblasts with more than 2 nuclei was found on final examination of pigs exposed to 500 and 100 ppm, but the difference was significant only at the 100-ppm level because of the variability at the higher level. A significant increase (p less than 0.004) in multinucleate cells was seen in the rats exposed to 500 ppm.

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.

Polycythemia vera: electron microscopy of the bone marrow in 10 non-treated patients. A thin section and freeze-fracture study

Electron microscopy (thin sections and freeze-fracture replicas) was performed on the bone marrow of ten patients with Polycythemia vera prior to any treatment. In addition to a hyperplasia of all three cell lineages and the sinuses, atypias were observed in the maturing erythroblasts. These aberrations of normal development consisted mainly of deep invaginations of the nuclear envelope in proerythroblasts and conspicuous nuclear clefts in erythro- and normoblasts. In comparison with similar changes in dyserythropoietic and aplastic anemia as well as leukemia these alterations are discussed in connection with disturbances of DNA synthesis. Further atypias involved megakaryopoiesis which displayed microforms probably as an evidence for maturation arrest. These ultrastructural abnormalities and their morphological features of a neoplastic proliferation of all three cell lineages in Polycythemia vera are in good agreement with the new concept of a transformation of a pluripotent stem cell with clonal character.

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.

Congenital dyserythropoietic anaemia type III: an electron microscopic study

The morphological features of erythroblasts in congenital dyserthropoietic anaemia (CDA) type III were studied by electron microscopy. Typical findings included clefts and blebs within the nuclear region, autolytic areas within cytoplasm, iron-filled mitochondria and myelin figures. The findings resembled those reported in other dyserythropoietic anaemias particularly in CDA type I; the main morphologic features which distinguished the two types were lack of spongy appearance of the chromatin, lack of cytoplasmic organelles within the nuclear region and intact nuclear envelope in CDA type III.

Comparative electron-microscopic study of the erythrocytic line in refractory anemia (preleukemia) and myelomonocytic leukemia

The bone marrow erythrocytic precursors of 12 patients with refractory anemia (preleukemia) or myelomonocytic leukemia were studied by transmission electron microscopy. The results were tabulated in a semiquantitative manner and a comparison was established between the two main diagnostic groups. The following results are reported. 1. Similar nuclear and cytoplasmic abnormalities of the normoblasts were observed in preleukemia and leukemia. 2. A nuclear lesion consisting of nuclear clefts and blebs was demonstrated in at least some of the normoblasts in all of the patients. Although not specific, this finding appears to be a new contribution in the field of preleukemia and myelomonocytic leukemia. 3. Iron overload, including the presence of pathologic sideroblasts, is common to both preleukemia and leukemia.

The morphology of dyserythropoiesis in a patient with acute erythroleukaemia associated with multiple myeloma

A patient with multiple myeloma in whom acute erythroleukaemia developed 5 years following treatment with irradiation and melphalan is reported. Immunoglobulin synthesis and immunofluorescence investigations provided evidence that the blast cells in the peripheral blood did not belong to the plasma cell series; ultrastructure examination demonstrated their myeloid origin. Chromosomally abnormal cells were observed in both the bone marrow and peripheral blood. Light-and electron microscopy of erythropoiesis in this case showed distinct features of dyserythropoiesis, similar to those described in other entities. The erythroid cell abnormalities are discussed in the light of their being either indications of malignancy or of a reactive process.

Intercellular contacts between erythroid precursors in the bone marrow in dyserythropoiesis

The ultrastructure of the cellular interfaces between erythroid precursors has been studied in both congenital and acquired dyserythropoiesis. The types of cell-to-cell contacts found included highly convoluated interdigitating septate-like junctions as well as apparent confluence of the cellular membranes of adjacent erythroid cells. Such findings are not characteristic of the intercellular relationships found in the normal erythroblastic islands. The erythroid plasma membrane modifications are possibly related to the changes in the plasma membranes of erythroid cells known to occur in dyserythropoiesis and their presence may well contribute to the ineffective erythropoiesis with intramedullary cell destruction which characterizes many dyserythropoietic states.