Dysmegakaryopoiesis in myelodysplastic syndromes (MDS): an immunomorphometric study of bone marrow trephine biopsy specimens.

An immunohistochemical and morphometric analysis was performed on trephine biopsy specimens of the bone marrow in 40 patients (23 men and 17 women, mean age 62 years) with different subtypes of myelodysplastic syndromes (MDS) to determine dysmegakaryopoiesis, but particularly precursor cells--that is, pro- and megakaryoblasts. In 31 of the 40 patients the numbers of megakaryocytes were increased which was associated with a predominance of smaller cell forms (micromegakaryocytes). Compared with periodic acid Schiff, immunostaining with a formalin resistant monoclonal antibody against glycoprotein IIIa (Y2/51(CD61) showed a clinically important proportion of immature elements. These could be designated pro- and megakaryoblasts by taking morphometric measurements on smears and bone marrow sections. There was a relevant increase in the number of promegakaryoblasts in 32 patients, consistent with uncontrolled expansion of the precursor pool. Seventeen repeated bone marrow biopsy specimens taken after chemotherapy largely showed a decrease in the numbers of megakaryocytes including the precursor cell population. Moreover, morphometric evaluation disclosed that micromegakaryocytes in MDS differ significantly from those in chronic myeloid leukaemia (CML) due to distinctive nuclear features and a disturbed nuclear:cytoplasmic ratio. These changes generate a more pleomorphic or atypical appearance of this cell population in MDS, compared with micromegakaryocytes in CML. It is concluded that the disproportionate increase in megakaryocyte precursors and the grossly abnormal aspects of micromegakaryocytes in MDS are characteristics of the severe defect involving haematopoiesis in this disorder.     

Myelodysplastic syndromes: Immunohistochemical and morphometric evaluation of proliferative activity in erythropoiesis and endoreduplicative capacity of megakaryocytes

An immunohistochemical and morphometric analysis was performed on bone marrow trephine biopsies in 40 patients with primary myelodysplastic syndromes (MDS) to evaluate the proliferative activity in erythropoiesis and the endoreduplicative capacity of megakaryocytes. Control groups included normal bone marrow and marrow from cases presenting with pernicious anaemia. Double-immunostaining was applied with a monoclonal antibody (PC10) directed against proliferating cell nuclear antigen (PCNA), followed by antibodies against glycophorin C (Ret40f) or platelet glycoprotein IIIa (Y2/51-CD61) for the identification of the erythroid and megakaryocytic cell lineage. Comparison with normal bone marrow showed a reduction of erythropoiesis accompanied by an increase in atypical (micro-) megakaryocytes. Erythroid precursors displayed significant enhancement of PCNA-immunostaining. Megakaryocytes showed no increase in the relative frequency of PC10-positive cells (PCNA-labelling index). In pernicious anaemia, predominance of macrocytic-megaloblastoid erythropoiesis was associated with a striking increase in PCNA-labelling. Cell kinetic studies in this disorder revealed an abnormal arrest, particularly in S-phase which generates an over-expression of PCNA. Similar conditions were believed to be present in MDS with secondary folate deficiency. This mechanism explains the relatively high rate of positively-reacting pro- and erythroblasts which is not invariably accompanied by an increase in cell proliferation. Determination of megakaryocyte size and PCNA-staining capacity resulted in a significant increase in PC10-positive cells among micromegakaryocytes. Our findings on this cell lineage are in keeping with the assumption of a block in endoreduplicative activity at higher ploidy levels, associated with an apparently not-deregulated endomitosis in small-sized megakaryocytes of lower ploidy stages.Supported by a grant from the Deutsche Forschungsgemeinschaft (DFG-Th 390/1-3)     

Structural changes in the megakaryocytes of patients infected with the human immune deficiency virus (HIV-1).

Although immune mechanisms are known to be partially responsible for the thrombocytopenia of patients infected with HIV-1, an understanding of the mechanism underlying this disorder is incomplete. A casual observation that bone marrow biopsies of HIV-infected individuals seem to exhibit an unusually large number of denuded megakaryocyte nuclei (DN-MK) prompted a study comparing MK of 20 HIV-seropositive individuals with those of 10 patients with HIV-negative idiopathic thrombocytopenic purpura and 10 hematologically normal subjects. In normal marrows the number of DN-MK average 2.1 +/- 0.5 SE per 10 low power field. In patients with ITP the average number was 6.5 +/- 1.4 SEM, whereas HIV-ITP marrows had an average of 42.5 +/- 3.7 SEM. Electron microscopy of AIDS megakaryocytes exhibited ballooning of the peripheral zone to an extent not seen by us in any other myelodysplastic syndromes. These observations support the concept that the pathophysiology affecting MK/platelets in HIV-infection should not be equated with the destructive process underlying other immune thrombocytopenias.     

Antiplatelet antibody‐induced thrombocytopenia does not correlate with megakaryocyte abnormalities in murine immune thrombocytopenia

Immune thrombocytopenia (ITP ) is an autoimmune bleeding disorder characterized by increased peripheral immune platelet destruction and megakaryocyte defects in the bone marrow. Although ITP was originally thought to be primarily due to antibody‐mediated autoimmunity, it is now clear that T cells also play a significant role in the disease. However, the exact interplay between platelet destruction, megakaryocyte dysfunction and the elements of both humoral and cell‐mediated immunity in ITP remains incompletely defined. While most studies have focused on immune platelet destruction in the spleen, an additional possibility is that the antiplatelet antibodies can also destroy bone marrow megakaryocytes. To address this, we negated the effects of T cells by utilizing an in vivo passive ITP model where BALB /c mice were administered various anti‐αII b, anti‐β3 or anti‐GPI b antibodies or antisera and platelet counts and bone marrow megakaryocytes were enumerated. Our results show that after 24 hours, all the different antiplatelet antibodies/sera induced variable degrees of thrombocytopenia in recipient mice. Compared with naïve control mice, however, histological examination of the bone marrow revealed that only 2 antibody preparations (mouse‐anti‐mouse β3 sera and an anti‐ αII b monoclonal antibody (MWR eg30) could affect bone marrow megakaryocyte counts. Our study shows that while most antiplatelet antibodies induce acute thrombocytopenia, the majority of them do not affect the number of megakaryocytes in the bone marrow. This suggests that other mechanisms may be responsible for megakaryocyte abnormalities seen during immune thrombocytopenia.     

Histomorphometry of bone marrow biopsies in primary osteomyelofibrosis/-sclerosis (agnogenic myeloid metaplasia) - correlations between clinical and morphological features

Summary Histomorphometry was performed on representative trephine biopsies of the bone marrow on admission of 50 patients (21 male, 29 female-age 67 years) with so-called primary osteomyelofibrosis/-sclerosis (OMF) not preceded by any other subtype of chronic myeloproliferative disorders. This study was firstly aimed at testing correlations between histological features (amount of haematopoiesis, cytological aspects of mega-karyocytes, density of reticulin and collagen fibres and degree of osteosclerosis) and laboratory data, as well as spleen size and duration of relevant prediagnostic symptoms. Secondly, we concentrated on a discrimination of OMF patients into two sub-groups according to bone marrow morphology and clinical variables. Statistical evaluation of histomorphometric variables and haematological findings disclosed that there was a progressive fibro-osteosclerotic process in the evolution of disease features. Increase in medullary fibrosis was significantly paralleled by an abnormal or pleomorphic megakaryopoiesis in the bone marrow: there was an increase in irregularity of perimeters for megakaryocytes and naked nuclei combined with smaller sizes of these elements including the nuclei. Additionally, there was a greater number of pycnotic bare nuclei. A number of morphometric features (density of fibres, degree of osteosclerosis, amount of haematopoiesis) were associated with corresponding clinical data (spleen size, length of preclinical history). By consideration of a set of basic histomorphometric variables our co-hort of 50 patients could be divided into an early hyperplastic subtype with no or minimal medullary reticulin and another group with conspicuous fibrotic and osteosclerotic alterations of the bone marrow. It was noticeable that we found no significant correlation between amount of haematopoiesis or marrow cellularity with splenomegaly. This result suggests that splenic haematopoiesis (myeloid metaplasia) may represent an autonomous or neoplastic process and not only compensation for a failing fibro-osteosclerotic bone marrow.Supported by a grant from the Deutsche Forschungsgemeinschaft (DFG-Th 390/1-1)     

Thrombopoietin-induced CXC chemokines,NAP-2 and PF4, suppress polyploidization and proplatelet formation during megakaryocyte maturation

BACKGROUND: We previously reported that the expressions of two CXC chemokines, neutrophil activating peptide-2 (NAP-2) and platelet factor-4 (PF-4), were induced by megakaryocyte-specific cytokine thrombopoietin (TPO) in mouse bone marrow megakaryocytes. The roles of these chemokines on megakaryocyte maturation/differentiation processes, including polyploidization and proplatelet formation (PPF) remain unresolved. RESULTS: NAP-2 and PF-4 suppressed the PPF of mature megakaryocytes freshly prepared from mouse bone marrow as well as that of the megakaryocyte progenitors, c-Kit+CD41+ cells, isolated from mouse bone marrow and cultured with TPO. NAP-2 and PF-4 inhibited polyploidization of c-Kit+CD41+ cells in the presence of TPO, and also inhibited the proliferation of c-Kit+CD41+ cells. CONCLUSIONS: NAP-2 and PF-4 produced by TPO stimulation in megakaryocytes suppress megakaryocyte maturation and proliferation as a feedback control.     

Platelet turnover and megakaryocytopoiesis in ITP

Among patients with ITP, a group of 9 subjects displayed a reduced platelet turnover. In their bone marrow the megakaryocyte mass was measured by 59Fe, and the results were referred to those of 6 patients with a moderately increased and of 6 with a considerably increased platelet turnover. In the low-turnover group the megakaryocyte nuclear lobe number was subnormal cells with basophil cytoplasm were in the majority and the number of megakaryocytes was increased, whereas in the other two groups of megakaryocite population showed a shift to the right, and increased nuclear lobe number, and the number of megakaryocytes, related to the erythroid cells, was increased. It is therefore assumed that in the case of a reduced platelet turnover, the megakaryocytes are damaged, primarily their maturation in the bone marrow. The three groups showed, however, no clinical differences.     

Defective alpha-granule production in megakaryocytes from gray platelet syndrome: ultrastructural studies of bone marrow cells and megakaryocytes growing in culture from blood precursors.

The ultrastructure and cytochemistry of megakaryocytes from two patients with a familial gray platelet syndrome are described. Although the Golgi zones appeared normally developed, the megakaryocytes lacked alpha-granules. Catalase-containing particles were normal in number. In immature megakaryocytes, granules measuring from 0.05-0.1 mu and having an electron-dense core occurred in the Golgi area. These granules, which are considered as the precursors of alpha-granules in normal megakaryocytes, appeared unable to mature, and their number decreased with the megakaryocyte maturation. The presence of dense material in distended demarcation membranes and/or vacuoles suggested that their content was discharged. It is suggested that myelofibrosis present in the bone marrow from these two patients may be related to the possible excretion of a polypeptide growth factor normally contained in the alpha-granules. Megakaryocytes grown by the plasma clot procedure from blood precursors isolated from the two patients also did not exhibit alpha-granules, which were replaced by vacuoles. Our findings suggest that the lack of alpha-granules in gray platelets may be related to a defective megakaryocyte-committed cell, and evidence is presented which suggests that the precursors of alpha-granules are produced but that their contents are then lost.     

Megakaryocytes and sinus walls in primary osteomyelofibrosis: transendothelial migration as revealed by three-dimensional reconstruction of serial sections following sequential double-immunostaining

Using sequential double-immunostaining and a newly-developed three-dimensional (3D-) reconstruction technique on serially cut sections from bone marrow trephines, we studied the transmural passage of megakaryocytes through the sinus wall. Biopsies derived from patients with primary (idiopathic) osteomyelofibrosis were exposed to monoclonal antibody against type IV collagen to delineate the sinus walls and also the frequently thickened basement membrane. Staining with the primary antibody was followed by Y2/51 (CD61) to identify all elements of megakaryopoiesis. In most instances serial sectioning and 3D-reconstruction revealed an amoeboid shape of megakaryocytes and a tandem-like arrangement in close spatial contact with the abluminal surface of the sinus wall. Preceded by formation of cytoplasmic processes, straight penetration of entire megakaryocytes through gaps in the sinus walls into the lumen was seen. Where collagen deposits apparently presented a barrier, a mole-like tunnelling through the basement membrane material (type IV collagen) was recognizable. Our findings are in keeping with the assumption that megakaryocyte locomotion is an essential requirement for normal thrombocytogenesis.     

Plasma glycocalicin. An aid in the classification of thrombocytopenic disorders

In some patients with thrombocytopenia, it is difficult to determine whether the condition is caused by underproduction of platelets (reduced numbers of megakaryocytes) or an increase in the rate of their destruction (normal or increased numbers of megakaryocytes). A non-invasive test to help distinguish between these two categories of thrombocytopenia would be useful. We related the plasma concentration of glycocalicin, a fragment of the platelet-membrane glycoprotein Ib, to the mechanism of thrombocytopenia by evaluating bone marrow megakaryocyte content and measuring platelet life span. Plasma glycocalicin was measured with a monoclonal antibody to the glycocalicin component of platelet glycoprotein Ib. The mean (+/- SD) plasma concentration of glycocalicin in 34 healthy controls was 87 +/- 20 percent of the level in pooled normal plasma (range, 52 to 127 percent). All of eight patients with aplastic anemia or amegakaryocytic thrombocytopenia confirmed by examining bone marrow (in all patients) and by determining the life span of autologous platelets (in six patients) had glycocalicin levels significantly below the normal range (5 to 27 percent). In contrast, each of 25 patients with thrombocytopenia thought to be caused by a reduction in platelet life span, whose bone marrow contained normal or increased numbers of megakaryocytes, had glycocalicin levels that fell within or above the normal range (48 to 261 percent). There was no overlap of values between the two patient populations. These studies indicate that the measurement of plasma glycocalicin may be a useful adjunct in classifying thrombocytopenic disorders.     

The relationship between ploidy and morphological classification of human megakaryocytes]

The relation between polyploidy and morphological classification of human megakaryocytes was studied in bone marrow aspirates from five normal individuals. On a Wright-Giemsa stained smear, megakaryocytes were morphologically classified into four groups according to a modification of Feinendegen's classification which is considered to reflect megakaryocyte maturation. The DNA of the morphologically classified cell is measured by microcytofluorometry using DAPI (4',6-diamidino-2-phenylindole) staining after removing the Wright-Giemsa stain. Most of the normal megakaryocytes were classified into type III (mature megakaryocytes) and the maximum peak in population of the megakaryocyte ploidy was observed at 16N. In each individual, the ploidy showed a similar pattern regardless of the classification. These findings suggest that the development of ploidy depends on a factor different from the one that determined the megakaryocyte maturation of cytoplasm and the ploidy is determined at the level of a megakaryocyte precursor or the most juvenile megakaryocyte.     

Localization of fibronectin in megakaryocytes of fetal liver

Antibodies specific for fibronectin were utilized to determine the sites of localization in the liver during development. The livers of fetal rats from each of gestation days 11-19, and from days 1 and 8 postpartum, were studied by fluorescence microscopy. Fibronectin was localized predominantly in megakaryocytes and megakaryocyte precursors, and to a lesser extent in the extracellular matrix surrounding blood vessels and between hepatocytes and sinusoids. The cytoplasm of megakaryocytes and their precursors displayed bright fluorescence but their nuclei were negative for fibronectin. Hepatocytes had negative or faint fluorescence. Megakaryocytes were present in the liver from day 12, and were numerous from day 13 through most of the rest of gestation. The relative numbers of megakaryocytes decreased in later gestation; at 8 days postpartum only a few were observed per section. Hepatic megakaryocytes appeared before megakaryocytes were established in spleen and bone marrow. The early and persistent high levels of fibronectin in hepatic megakaryocytes, in the absence of comparable localization within hepatocytes, leads us to the hypothesis that megakaryocytes are important in establishing circulating fibronectin levels in the fetus. Similarly, bone marrow megakaryocytes may contribute to circulating fibronectin in the adult.     

Megakaryocytes in myelodysplasia: an immunohistochemical study on bone marrow trephines

Megakaryocytes in 63 bone marrow trephine biopsies were examined for their staining characteristics, location and size distribution using the monoclonal antibody Y2/51 directed against platelet glycoprotein IIIa (CD61). Megakaryocytes in normal bone marrow were evenly distributed and demonstrated homogeneous staining with Y2/51. In addition, there was little variation in their size or shape. In contrast, myelodysplastic and myeloproliferative bone marrow trephines showed considerable dysmegakaryopoiesis demonstrated by heterogeneity of staining, an altered architectural distribution with a predominantly paratrabecular location and considerable variation in size and shape. Furthermore, in myelodysplasia 25% of the CD61 positive cells were micromegakaryocytes as opposed to less than 10% in normal or reactive marrows. Such dysmegakaryopoiesis is believed to be a clinically important feature of myelodysplasia, although until now it has only been possible to assess it subjectively. The availability of the monoclonal antibody Y2/51 provides a rapid and reproducible means of studying megakaryocyte size, shape and distribution in routine trephine specimens and may help to overcome some of the diagnostic problems currently associated with myelodysplasia and other intrinsic bone marrow neoplasias.     

The platelet volume-number relationship in patients infected with the human immunodeficiency virus

The pathophysiology of thrombocytopenia in the acquired immune deficiency syndrome has not been elucidated completely. Many findings in these patients are identical to those with immune thrombocytopenic purpura. However, recent findings in acquired immune deficiency syndrome patients including the effect of zidovudine on platelet count and the demonstration of ultrastructural changes and viral RNA in megakaryocytes, have suggested that the human immunodeficiency virus may directly infect megakaryocytes, and play a role in acquired immune deficiency syndrome-related thrombocytopenia. To investigate further the mechanism of decreased platelet counts in human immunodeficiency virus-infected patients, the platelet volume-number relationship and corresponding bone marrow findings in 34 patients infected with human immunodeficiency virus were studied. Parameters evaluated included platelet count and mean platelet volume; bone marrow cellularity, megakaryocyte number, and number and percentage of denuded megakaryocyte nuclei. Two thirds of the platelet counts were low, and of these 92% had an inappropriately low mean platelet volume. These individuals had a platelet-volume number relationship that is very similar to that seen in myelosuppressive disorders. In addition, more than 90% of the bone marrows from thrombocytopenic patients had either normal or decreased numbers of megakaryocytes. These observations provide additional evidence to support the hypothesis that the pathophysiology of human immunodeficiency virus-associated thrombocytopenia may be due, at least in part, to a direct effect on the megakaryocytes.     

Megakaryocytes carry the fused bcr-abl gene in chronic myeloid leukaemia: a fluorescence in situ hybridization analysis from bone marrow biopsies

Histological examination of bone marrow biopsies shows that about one-third of chronic myeloid leukaemia (CML) patients exhibit an increase of megakaryocytes. The megakaryocytic predominance may be so striking that differentiation from other chronic myeloproliferative disorders (CMPD) may be difficult in some CML patients. Megakaryocytes in CML are clonal as demonstrated by loss of glucose-6-phosphate dehydrogenase isoenzymes. The Ph translocation, fusing the abl and bcr genes on chromosomes 9 and 22, however, obviously occurs as a second step in tumour development. So far, the Ph translocation has not been assigned explicitly to megakaryocytes. The question is whether the megakaryocytic cell lineage could harbour the bcr/abl fusion in those CML cases with striking proliferation of megakaryocytes but lack this genetic defect in cases with normal or decreased megakaryocyte counts. We therefore performed triple-colour fluorescence in situ hybridization (FISH) for portions of the bcr and abl genes flanking the breakpoint in CML in paraffin sections of CML cases with normal and with increased numbers of megakaryocytes. This method allows identification of the bcr/abl fusion in single, morphologically intact cells, whereas conventional cytogenetics requires lysis and thus destruction of the cell. Among the 21 CML patients examined by FISH, 10 were informative for bcr and abl genes and displayed distinct hybridization signals within nuclei of bone marrow cells. Besides the granulopoietic cells, megakaryocytes of all those patients (4 without and 6 with varying grades of megakaryocytic increase) displayed bcr/abl fusion signals indiciative of a Ph translocation. The lack of hybridization signals in the remaining 11 cases indicates that this technique is not of value diagnostically and should be reserved for scientific questions. Positive controls consisted of conventional chromosome preparations from bone marrow aspirates demonstrating the Ph chromosome in all patients examined, and negative controls of paraffin sections of bone marrow biopsies from non-CML patients. These showed no fusion signals in bone marrow cells, including megakaryocytes, using FISH. Our results demonstrate clearly that not only the transforming event but also the Ph translocation leading to the bcr/abl fusion happens prior to the differentiation of the pluripotent stem cell into different myeloid lineages. The megakaryocytic proliferation evident in some CML cases is probably a consequence of the disease progress.     

Thrombopoietin administered during induction chemotherapy to patients with acute myeloid leukemia induces transient morphologic changes that may resemble chronic myeloproliferative disorders

Thrombopoietin (TPO), a potent stimulator of megakaryocyte and platelet production, has been used in clinical trials to reduce thrombocytopenia after chemotherapy in patients with acute myeloid leukemia (AML). We report that TPO therapy is associated with peripheral blood and bone marrow findings that can mimic myeloproliferative disorders. Peripheral blood and bone marrow samples of 13 patients with AML who received TPO were examined. A subset of bone marrow samples exhibited hypercellularity, megakaryocytic hyperplasia, and reticulin fibrosis after TPO administration. Cases demonstrated as many as 58.4 megakaryocytes per high-powerfield (MHPF) compared with 3.7 MHPF in the control group. Megakaryocytic atypia, increased mitoses, emperipolesis, intrasinusoidal megakaryocytes, and thickened trabeculae also were seen. Peripheral blood findings included leukoerythroblastosis, leukocytosis, thrombocytosis, and circulating megakaryocyte nuclei. Changes resolved within 3 months after discontinuation of TPO. This rapid resolution of the morphologic abnormalities induced by TPO distinguishes these findings from those seen in true chronic myeloproliferative disorders.     

LAT (linker for activation of T cells): a useful marker for megakaryocyte evaluation on bone marrow biopsies

Detection of atypical megakaryocytes in bone marrow biopsies, especially in cases of myelodysplastic syndromes (MDS), chronic myeloproliferative disorders (CMPD) and acute leukemias, is facilitated by staining for markers such as Ulex europaeus agglutinin (UEA)-J, CD31, CD61 and von Willebrand factor (VWF), the latter being considered the most sensitive. Recently, LAT (linker for activation of T cells), a molecule involved in T-cell activation and platelet aggregation, was found to be expressed by megakaryocytes and platelets in tissue sections. We compared VWF and LAT immunoreactivity on megakaryocytes in 64 bone marrow biopsies from 12 normal controls (NC), and from patients with MDS (n=18), CMPD (n=21) and acute megakaryocytic leukemia (AML-M7, n=13). Immunostaining was performed on paraffin sections with polyclonal antibodies against VWF and LAT. Immunoreactivity was evaluated by counting positive megakaryocytes in 10 high-power fields, and values were compared using Student's t test for paired data. Both VWF and LAT predominantly stained the cytoplasm of megakaryocytes, although LAT was also recognizable on the cell membrane. In most biopsies, the immunoreactivity of the two antibodies was quite similar. No significant differences were noticed between the mean values of VWF+ and LAT+ megakaryocytes. However, in 22 cases (5 NC; 5 MDS; 6 CMPD; 6 AML-M7), the number of LAT+ megakaryocytes was at least 30% higher than VWF+cells, while in 3 cases opposite findings were found. In 3 AML-M7 cases, anti-LAT antibodies stained numerous megakaryocytes, but anti-VWF staining was practically negative; in another 5 AML-M7 cases, anti-LAT labeling was much stronger than anti-VWF staining. LAT represents a useful immunohistochemical marker for megakaryocytes in normal and pathological conditions. It seems to be expressed by megakaryocytes more than VWF in most cases and, particularly, in conditions associated with poorly differentiated megakaryocytes, such as acute megakaryocytic leukemias. The use of LAT staining should be recommended in association with other megakaryocyte markers in the study of bone marrow biopsies in cases of hematopoietic disorders.     

Microcytofluorometrical measurement of DNA content in immunologically identified micromegakaryocytes of human bone marrow

We have developed a method to microfluorometrically determine the amount of DNA in immunologically identified micromegakaryocytes on bone marrow smears. Bone marrow smears were fixed with acetone-formalin buffer and immunostained with a monoclonal anti-GPIIb/IIIa antibody, followed by FITC conjugated anti-mouse IgG. After the smears were re-fixed with methanol, DAPI (4', 6-diamidino-2-phenylindole) staining was performed. Using an automatic Digital-Microfluorometer (Olympus MMSP-FR-II), megakaryocytes on the smears were identifies by the GPIIb/IIIa immunofluorescence and, after changing the barrier filters, their nuclear DNA content was measured by the intensity of DAPI fluorescence, which is proportional to the amount of DNA. Using this method, we found that the DNA histogram of the megakaryocytes from a patient with myelodysplastic syndrome showed a shift to small ploidy compared with normal controls. This method may be valuable in the measurement of the megakaryocyte DNA content.     

The histological characterization of ALIP in the myelodysplastic syndromes

Bone marrow biopsies of patients with a myelodysplastic syndrome (MDS) may, in the absence of an increased number of blasts in the bone marrow smears, contain small clusters of immature precursors. The presence of these cell nests, previously described as "abnormal localized immature precursors" or ALIP, bears a strong prognostic value predisposing patients to early death with an increased risk to develop myeloid leukaemia. In order to describe and delineate this histological characteristic more precisely, we compared bone biopsies of patients with MDS, used in these previous studies, with bone marrow biopsies performed for staging procedures in patients with Hodgkin's disease, non-Hodgkin's lymphoma and carcinoma. From this comparison we conclude that immature precursors are readily differentiated from proerythroblasts, myeloblasts and small-sized megakaryocytes, and that they most probably represent precursors of the myelo-monocytic-erythroid series. A clearcut increase in their number, mostly resulting in the formation of small clusters, is only found in biopsies from patients with MDS.     

Hypothesis: a possible role for interferon in the treatment of idiopathic myelofibrosis

It is proposed that interferon may be an active agent in the treatment of patients with idiopathic myelofibrosis. In this disorder the megakaryocyte cell lineage plays a major role in the deposition of bone marrow collagen by the release of growth promoting factors, including platelet-derived growth factor, which are mitogenic for fibroblast proliferation. Interferon reduces collagen deposition in the bone marrow by suppressing the activity of the proto-oncogene, which is involved in the production of growth factors from abnormal megakaryocytes and platelets. A direct myeloid cytoreductive effect of interferon upon the megakaryocyte proliferation contributes to reducing growth factor activity in the bone marrow. Finally, interferon induces monocytoid differentiation, thereby increasing bone marrow collagenase-activity. Thus, interferon has several actions, which in concert might reduce bone marrow collagen in myelofibrosis.