Bone marrow features and clinical findings in chronic myeloid leukemia--a comparative, multicenter, immunohistological and morphometric study on 614 patients

A multicenter, immunohistochemical and morphometric study was performed on diagnostic pretreatment bone marrow biopsies in 614 adult patients with Ph1+ chronic myeloid leukemia (CML) to compare histological features with clinical findings. For identification of megakaryopoiesis we used the monoclonal antibody CD61 and additionally the PAS reaction to determine the subfraction of atypical micromegakaryocytes and precursors. Labelling of erythroid precursors was carried out by a monoclonal antibody directed against glycophorin C. In order to selectively stain macrophages and their activated subset we applied CD68 and the GSA-I lectin. Density of argyrophilic fibers (reticulin plus collagen) was measured following Gomori's silver impregnation method. In accordance with laboratory data morphological variables revealed a comparable amount of congruence in the various groups of CML patients derived from different sources. In about 26% of patients early (reticulin) to advanced (collagen) fibrosis was detectable. Significant correlations were calculated between the extent of myelofibrosis with splenomegaly, anemia and increasing numbers of erythroblasts and myeloblasts in the peripheral blood count. These features were assumed to indicate more advanced stages of the disease process with ensuing transition into myeloid metaplasia and consequently were associated with an unfavorable prognosis. Significant relationships were revealed between the number of CD61+ megakaryocytes and more important, also their precursor fraction with the degree of fibrosis. This result extends previous experimental findings regarding the impact of immature elements of this cell lineage for the generation of myelofibrosis. The significant association of erythroid precursors with the number of mature (resident) macrophages including their activated GSA-I subset may shed some light on their functional involvement in iron turnover and hemoglobin synthesis. A modified histological classification of predominant bone marrow features is introduced. This simplified synthesis staging system (Cologne Classification) is not only associated with certain sets of laboratory data, but also with different survival patterns.     

Progression of bone marrow fibrosis in patients with essential thrombocythemia and polycythemia vera during anagrelide treatment

Anagrelide is a second-line option for reduction of thrombocythemia in patients with chronic myeloproliferative disorders (CMPDs). A multicenter, open, phase II study of anagrelide treatment in 60 patients during 2 yr was performed by the Swedish Myeloproliferative Disorder Study Group. Adequate bone marrow biopsies were obtained from 53 of the CMPD patients [36 essential thrombocythemia (ET), 16 polycythemia vera (PV), 1 chronic idiopathic myelofibrosis (CIMF)] before treatment and compared with biopsies from 30 healthy volunteers and 34 patients with acute myeloid leukemia (AML). Higher reticulin and hyaluronan (HYA) scores were found before anagrelide therapy in the CMPD patients than in the normal controls (p<0.001 and p<0.001, respectively) and AML patients (p<0.001 and p=0.011, respectively). At the end of the study 30 CMPD patients were still on anagrelide treatment and in 19 of these patients, all diagnosed as ET (n=16) or PV (n=3), pretreatment bone marrow biopsies were compared with follow-up samples. After 2 yr of anagrelide therapy the reticulin and HYA scores were significantly higher than before treatment (p=0.02 and p=0.002, respectively). The cellularity was significantly higher (p=0.014), although the number of megakaryocytes did not change significantly. The increase of reticulin and HYA in the bone marrow after 2 yr of treatment with anagrelide indicated progression of fibrosis. Although anagrelide is a valuable drug for reduction of platelet levels, it seems unable to stop progression of bone marrow fibrosis and hypercellularity in ET and PV.     

Analysis of risk factors of the evolution of myelofibrosis in pre-fibrotic chronic idiopathic myelofibrosis: a retrospective study based on follow up biopsies of 70 patients by using the RECPAM method

The advanced, fibrotic phase of chronic idiopathic myelofibrosis (CIMF) is preceded by a pre-fibrotic stage. However, the factors which may influence or predict the development of myelofibrosis are not well established. Thus we investigated follow up biopsies of 70 patients with CIMF, diagnosed in stages of no or only scant fiber increase, for the development of myelofibrosis. The influence of histopathological (megakaryocytes, initial fiber content), clinical (age, gender, splenomegaly, chemotherapy) and hematological (Hb, leukocyte- and platelet count) parameters on the development of myelofibrosis was evaluated by using the univariate Log Rank method and the multivariate recursive partition and amalgamation (RECPAM) analysis. Surveying a mean observation period of 47 months we found a development of significant myelofibrosis in 30 of the 70 patients. In the univariate analysis, the development of myelofibrosis was associated with increased megakaryocytes, initial fiber content and age of the patient. In the RECPAM analysis, the patients with a high megakaryocytic count and older age showed the highest risk of developing myelofibrosis (mean 58.3 and 60.1 months). The group with the best prognosis comprised the patients under 60 years which have a low content of megakaryocytes (mean 137 months). We found that the development of myelofibrosis in CIMF was best predicted by an increase of megakaryocytes within the bone marrow, possibly reflecting the release of growth factors by these cells. The next important risk factor was the age of the patients.     

Bone marrow CD34+ progenitor cells in Philadelphia chromosome-negative chronic myeloproliferative disorders--a clinicopathological study on 575 patients

Contrasting the circulating CD34⁺ hematopoietic progenitor cells (HPCs) in chronic myeloproliferative disorders (CMPDs), scant knowledge is available regarding their quantity in the bone marrow (BM). Therefore, a clinicopathological study was performed on trephine biopsies in 575 patients with CMPDs focused on chronic idiopathic myelofibrosis (CIMF). A comparison with 25 healthy subjects revealed no significant differences in the numbers of HPCs (6 ± 3/mm²) in polycythemia vera, essential thrombocythemia and advanced fibro-osteosclerotic stages of CIMF. Pre-fibrotic and early-stage CIMF displayed 16 ± 11 precursors per mm² BM. Sequential biopsies in this disorder showed a decline in HPCs (10 ± 6/mm²) with evolving myelofibrosis - myeloid metaplasia (MMM), while in terminal stages acceleration generated an increase (24 ± 25/mm²). A significant association between the quantity of HPCs and the development of myelofibrosis, splenomegaly, and anemia as well as an increase in peripheral blasts was recognizable in CIMF. Moreover, in all subtypes of CMPDs, a favorable prognosis was significantly associated with a higher number of HPCs in the BM. In conclusion, enhanced inflow of precursors from the BM with subsequent trapping, self-renewal and mobilization by the spleen is assumed to indicate a progressive generalization and worsening of the outcome. This putative pathomechanism is significantly associated with the evolution of MMM.     

急性白血病治疗前后骨髓网硬蛋白纤维含量的初步研究

目的 应用经塑料包埋骨髓活组织切片技术研究骨髓网硬蛋白纤维与白血病细胞的消长关系。方法 采用Ｇomori染色行Ｍasson三色染色检测１６例急性白血病患者治疗前后骨髓网硬蛋白纤维含量变化。结果 １６例急性白血病患者治疗前后骨髓网硬蛋白纤维阳性例数有明显差异（Ｐ＜０．０５）。治疗后骨髓网硬蛋白纤维含量呈正常１１例，其中完全缓解（ＣＲ）８例，部分缓解（ＰＲ）３例；而治疗后骨髓网硬蛋白纤维呈异常５例，其中ＰＲ１例     

Megakaryocyte induced fibroblast proliferation is enhanced by costimulation with IL-6/IL-3 and dependent on secretory and adhesion events.

Experimental data are in keeping with the finding that megakaryocytes isolated from normal human bone marrow may promote fibroblast growth. This effect can be significantly enhanced by interleukin (IL)-3. In this context it has been demonstrated that IL-3 induces the release of platelet-derived growth factor (PDGF) and transforming growth factor beta1 (TGFbeta1) from megakaryocytes, factors known to enhance fibroblast proliferation. The present in vitro study was performed to elucidate the action of several other cytokines which are able to influence the different steps of megakaryocyte maturation and function like stem cell factor (SCF), IL-6, and leukemia inhibitory factor (LIF) as well. Following an appropriate experimental design we were able to show that none of the mentioned cytokines enhanced megakaryocyte dependent fibroblast proliferation in the coculture assays. On the other hand, IL-6 in combination with IL-3 surpassed the IL-3 dependent action significantly. However, the combined IL-3/IL-6 effect was not explainable by an increased PDGF/TGF-beta secretion of the megakaryocytes. In transwell experiments the inhibition of cell-to-cell contact via tissue culture inserts generated a conspicuous impairment of fibroblast growth in the IL-3/IL-6 treated cocultures. This reversal surpassed even the effect on the untreated and IL-3 stimulated cocultures. Hence, a direct contact of both cell types probably inducing adhesion phenomenons and warranting a certain threshold of local PDGF/TGF-beta concentration is a prerequisite for the proliferative effect on fibroblasts in the costimulation experiments. These results are of special interest regarding the evolution of myelofibrosis in chronic myeloproliferative disorders (CMPDs) because (1) various progenitor cells including the megakaryocytic lineage are hypersensitive towards IL-3 and (2) an abnormal secretion of IL-6 is described for megakaryocytes in these disorders.     

Autoimmune myelofibrosis: report of three cases and review of the literature

Autoimmune myelofibrosis is a distinct clinicopathological entity, recognizing immunopathogenetic mechanisms and occurring isolately or in association with systemic and/or organ-specific autoimmune diseases. It results in chronic cytopenias, and is defined by a pattern including bone marrow, peripheral blood, serological and clinical features. It has to be distinguished from other disorders having myelofibrosis. Among these, the most relevant differential diagnosis is with chronic idiopathic myelofibrosis, particularly when disclosing autoimmune clinical and/or laboratory features as epiphenomenon related to a secondary immune-dysregulation. Here we report on 3 patients admitted because of chronic cytopenias. In all of them, the clinicopathological evaluation essentially demonstrated myelofibrosis, not clustered megakaryocytes, reactive lymphoid infiltration in marrow biopsies, absence of significant tear-drop poikilocytosis and leukoerythroblastosis on peripheral blood smears, normal-sized spleen, positive autoimmune serology. The resulting patterns met the diagnosis of autoimmune myelofibrosis occurring isolately in a patient and associated with Sj?gren's syndrome or concomitant Sj?gren's syndrome and Hashimoto's thyroiditis in the other two, respectively. Transient improvements in cytopenias and unmodified myelofibrosis were observed following corticosteroid treatment. It is noteworthy the lack of a specific therapy, being the underlying pathophisiology of myelofibrosis still unclear. In conclusion, increased awareness of the clinicopathological pattern identifying autoimmune myelofibrosis is recommended in order to improve basic and clinical knowledge of this emerging entity.     

恶性血液病继发骨髓纤维化71例病理及临床研究

 【摘要】 目的 探讨继发性骨髓纤维化(secondary myelofibrosis,SMF)患者的临床及骨髓病理学特征。方法 对71例继发性骨髓纤维化患者的临床表现、外周血涂片、骨髓涂片及骨髓活检情况进行了回顾性研究,同时对不同疾病骨髓纤维化程度与巨核细胞数目作了相关分析。结果 分析71例SMF患者,其原发病情况为慢性粒细胞白血病(CML)20例(28.2%),急性淋巴细胞白血病（ALL）6例（8.5%）,急性髓系细胞白血病(AML)、骨髓增生异常综合症（MDS）、淋巴瘤各10例（14.1%）,多发性骨髓瘤（MM）、淋巴增殖性疾病（LPD）各4例（5.6%）,骨髓增殖性肿瘤（MPN）3例,慢性淋巴细胞白血病（CLL）2例,骨髓转移癌、传染性单核细胞增多症各1例。骨髓纤维化程度与巨核细胞数具有明显相关性（P＜0.05）。结论 继发性骨髓纤维化患者骨髓切片巨核细胞增生明显,且与纤维化程度有相关性。这可能与巨核细胞克隆性增殖释放的多种细胞因子积极参与骨纤的发生发展密切相关。     

Statins in the treatment of polycythaemia vera and allied disorders: an antithrombotic and cytoreductive potential?

Thrombohaemorrhagic complications are major clinical problems in the classical chronic Ph-negative myeloproliferative disorders (CMPDs), polycytaemia vera (PV), essential thrombocythaemia (ET) and idiopathic myelofibrosis (IMF), contributing significantly to morbidity and mortality. Pathophysiologically these disorders are characterized by clonal myeloproliferation, myeloaccumulation and a propensity to develop myelofibrosis and neoangiogenesis in both the bone marrow and spleen. Based upon in vitro and in vivo studies of the effects of statins (antithrombotic, antiproliferative, proapoptotic and antiangiogenic), this review focuses on the translation of these effects into potential clinical benefits of statin therapy in patients with CMPDs.     

Clonal Analysis of Agnogenic Myeloid Metaplasia

Agnogenic myeloid metaplasia (AMM) is a chronic myeloproliferative disorder that leads to a sustained proliferation of megakaryocytes and an increase of reticulin fibers within the bone marrow. Blood and bone marrow samples from patients with advanced AMM with fully developed myelofibrosis as well as cases in the cellular phase of the disease were investigated for clonality. Clonality was studied by X-linked restriction length polymorphism in conjunction with DNA methylation patterns. Granulocytes and total bone marrow cells proved to be monoclonal in origin whereas at least a minor portion of the peripheral lymphocytes were not clonally derived. Our findings indicate that the cellular phase of AMM as well as the fully developed disease progressed to myelofibrosis represent a monoclonal proliferation of pluripotent hematopoietic stem cells.     

Detection of the JAK2V617F mutation by asymmetric PCR and melt curve analysis

The chronic myeloproliferative disorders (CMPDs) are a heterogeneous group of clonal hematopoietic diseases characterized by production of increased numbers of mature leukocytes, erythrocytes, and/or platelets. Clinically these disorders are often insidious in onset, produce nonspecific thrombotic or hemorrhagic complications, and can be easily confused with a variety of benign, reactive conditions. Thus, confirming a CMPD can be difficult as it is often a diagnosis of exclusion. The recently identified JAK2(V617F) mutation is frequently present in the classic CMPDs polycythemia vera, essential thrombocythemia, and chronic idiopathic myelofibrosis. JAK2(V617F) determination has proven to be a useful diagnostic tool in patients with some clinical features suggestive for a CMPD, and may have benefit as a way to monitor known disease. There are several published molecular assays for the JAK2(V617F) target, of variable sensitivity and technical complexity, many of which are not easily replicated in a typical clinical laboratory. We present a robust, sensitive PCR/melt curve assay for the JAK2(V617F) mutation which uses the widely available Roche LightCycler platform, and is thus applicable to many clinical molecular laboratories.     

Dynamics of fibrosis in chronic idiopathic (primary) myelofibrosis during therapy: a follow-up study on 309 patients

Controversial issues in chronic idiopathic myelofibrosis (IMF) are amongst others the evolution of the disease process and the influence of therapy on the dynamics of fibrosis. For this reason, a multicenter observational study was performed on 309 patients with IMF that had a long follow-up including 822 bone marrow biopsies at a median interval of 32 months. In addition to a control group (156 patients) with symptomatic treatment, monotherapy consisted of busulfan (30 patients), hydroxyurea (52 patients), interferon (26 patients) and various combinations (48 patients). Density and quality (reticulin/collagen) of fibers was determined by a semiquantitative scoring system. Independent of therapeutic regimens at the time of the last bone marrow biopsy 67% of the patients with grades 0-2 fibrosis revealed a progression, 42% stable state and 6% regression of myelofibrosis. Because of significant differences concerning frequencies of biopsies and endpoints of examinations, individual changes in the grades of fibrosis were evaluated with regard to treatment applied at standardized intervals of 20 months. According to this calculation no relevant differences in the dynamics of myelofibrosis (progression, stable state) was detectable in the control group compared to the other therapeutic modalities. The few patients with a regression of myelofibrosis usually presented with severe hypoplasia compatible with a myelo-ablative effect by aggressive chemotherapy. In conclusion, persuasive evidence has been produced that myelofibrosis in IMF is characterized by a stepwise progression and that this process is not significantly influenced by current treatment strategies.     

Chronic myeloproliferative disorders: a tyrosine kinase tale.

Chronic myeloproliferative diseases (CMPDs) are characterized by the abnormal proliferation and survival of one or more myeloid cell types. The archetype of this class of hematological diseases is chronic myeloid leukemia (CML), characterized by the presence of the Philadelphia (Ph) chromosome, the result of t(9;22)(q34;q11), and the associated BCR-ABL1 oncogene. Some of the Ph-negative myeloproliferative diseases are characterized by other chromosomal translocations involving a variety of tyrosine kinase genes, including ABL1, ABL2, PDGFRA, PDGFRB, FGFR1, and JAK2. The majority of Ph-negative CMPDs, however, such as chronic eosinophilic leukemia, polycythemia vera, essential thrombocythemia, and idiopathic myelofibrosis are not characterized by the presence of recurrent chromosomal abnormalities. Recent studies have identified the FIP1L1-PDGFRA fusion gene, generated due to a small cryptic deletion on chromosome 4q12, and the activating V617F mutation in JAK2 in a significant fraction of Ph-negative CMPDs. These results show that abnormalities in tyrosine kinase genes are central to the molecular pathogenesis of CMPDs. Genome-wide screenings to identify novel tyrosine kinase abnormalities in CMPDs may contribute to further improvement of the diagnosis and the treatment of these diseases.     

TGF-β and Megakaryocytes in the Pathogenesis of Myelofibrosis in Myeloproliferative Disorders

Myeloproliferative disorders are clonal disorders of the hematopoietic stem cell and comprise a spectrum of more or less well-defined clinical entities: polycythaemia vera, chronic myeloid leukemia, essential thrombocythaemia, and agnogenic myeloid metaplasia. Myelofibrosis, which contributes substantially to the impaired hematopoiesis, is commonly observed in myeloproliferative disorders but it represents the criterion of agnogenic myeloid metaplasia also termed idiopathic myelofibrosis. Although progress has been made in the elucidation of the pathogenesis of myelofibrosis, it still remains unclear. The aim of this review is to adress the new insights that outline the potential role of TGF-β in the promotion of myelofibrosis, through its release from megakaryocytes/platelets, particularly in agnogenic myeloid metaplasia.     

Fibre content and cellularity of the bone marrow of the iliac crest, vertebral column and sternum in chronic myeloproliferative disorders

Heterogeneous content of fibres and haematopoesis within the bone marrow may affect diagnosis and staging in chronic myeloproliferative disorders (CMPDs). To evaluate their distribution, we conducted a post mortem histomorphometric study of 22 patients with CMPD in chronic phases. In bone marrow specimens from the anterior and posterior iliac crest (right and left of each), the sternum, the 7th thoracic and the 3rd lumbar vertebra, the argyrophil fibres were counted using the line intersection method and the cellular and fatty bone marrow using the point count method. Statistical analysis was performed by direct comparison of the sites. The distribution of fibres was almost homogeneous in the patients with low fibre content, revealing a random diversity in more advanced stages of marrow fibrosis. 1/22 patient had no fibre increase in one specimen of the iliac crest and overt myelofibrosis in the other sites. 1/22 patient had myelofibrosis in two sites of the iliac crest and no fibre increase in vertebral column and sternum. The bone marrow cellularity was almost homogeneously increased in all patients. Myelofibrosis proved to be a generalised process with heterogeneous grades of severity in different regions of the bone marrow in CMPDs. No topographical bias was found. In contrast to the homogeneous increase of the bone marrow cellularity the topographical heterogeneity of the fibre content may limit the representativity of single bone marrow biopsies in patients with CMPDs.     

Primary myelofibrosis is the most frequent myeloproliferative neoplasm associated with del(5q): clinicopathologic comparison of del(5q)-positive and -negative cases

Among 23 cases of myeloproliferative neoplasms (MPNs) with an associated del(5q) seen at our institution, 14 (61%) fulfilled diagnostic criteria for primary myelofibrosis (PMF). Other diagnoses included polycythemia vera (PV; n = 2), essential thrombocythemia (ET; n = 1), post-ET myelofibrosis (n = 1), systemic mastocytosis (SM; n = 1), and MPN, unclassifiable (n = 4). Compared to their del(5q)-negative counterparts, del(5q)-positive PMF cases were significantly more anemic (p < 0.001) and thrombocytopenic (p < 0.001). However, survival and leukemic transformation rates appear to be similar between the two groups. del(5q)-positive PMF was histologically characterized by a mixture of both small and monolobated megakaryocytes as well as large and bizarre megakaryocytes. When used, lenalidomide therapy induced hematological and cytogenetic remissions in del(5q)-positive PMF. The current study identifies PMF as another del(5q)-associated myeloid malignancy with characteristic megakaryocyte morphology.     

Chronic idiopathic myelofibrosis terminating in extramedullary anaplastic plasmacytoma

Chronic idiopathic myelofibrosis (CIMF) is a chronic myeloproliferative disorder (CMPD) with progressive fibrosis and extramedullary hematopoiesis. Similar to other CMPDs, the stem cell in CIMF has the potential to differentiate into myeloid or lymphoid lineages, and thus CIMF can culminate in acute leukemia of myeloid or, rarely, lymphoid lineage. We describe an unusual case of CIMF terminating in extramedullary anaplastic plasmacytoma. The patient was a 61-year-old male with an 11-year history of CIMF. His course was complicated by rapidly growing abdominal and inguinal lymphadenopathy. Lymph node biopsy revealed a diffuse undifferentiated infiltrate in the background of extramedullary hematopoiesis. Flow cytometric and immunohistochemical analysis demonstrated plasma cell-related antigens (CD138, CD38, cytoplasmic kappa light chain), epithelial membrane antigen and CD43 in the tumor cells. The myeloid, B-cell or T-cell markers were negative. A clonal immunoglobulin heavy chain gene rearrangement was identified by polymerase chain reaction. The plasma cell origin was further confirmed by electron microscopic examination, which revealed stacks of rough endoplasmic reticulum. Monoclonal gammopathy may occur in CIMF, and rare cases of simultaneous plasma cell myeloma and CIMF have been reported in the literature. However, to the best of our knowledge, this is the first report of CIMF terminating in extramedullary anaplastic plasmacytoma.     

Essential thrombocythemia or chronic idiopathic myelofibrosis? A single-center study based on hematopoietic bone marrow histology

We reviewed a large series of patients with essential thrombocythemia diagnosed on the basis of the Polycythemia Vera Study Group criteria, and reclassified them by evaluating their major morphologic features and clinical course using the World Health Organization classification. The morphologic review of the bone marrow biopsies of 116 patients (44 males and 72 females; aged 19 - 83 years, median 55 years; median follow-up 121 months) led to 22 cases (19%) being classified as essential thrombocythemia (ET), 24 (21%) as chronic idiopathic myelofibrosis (CIMF)-0, 44 (37%) as CIMF-1, 13 (12%) as CIMF-2, 9 (8%) as latent phase polycythemia vera, and four (3%) as chronic myeloproliferative disorder, unclassifiable. There was a significant difference in the median age of the ET and fibrotic CIMF patients (54.7 +/- 13.55 vs. 59.13 +/- 15.05 years; P = 0.03). Histologic analysis showed that the simultaneous presence of loose clusters of large/giant megakaryocytes and nuclear hyperlobulation was significantly different between the ET and the prefibrotic CIMF (P<0.01) and fibrotic CIMF patients (P<0.01), and that the association of dense clusters of megakaryocytes with maturation defects and bulbous nuclei also distinguished the prefibrotic CIMF (P<0.05) and fibrotic CIMF patients (P<0.001) from those with ET. The association of cellularity, granulocytic proliferation and reticulin fibers was helpful in distinguishing prefibrotic from fibrotic CIMF (P<0.001).     

Polycythemia vera megakaryocytes store and release lysozyme to a higher extent than megakaryocytes in secondary polycythemia (polyglobuly)

Lysozyme, a myelomonocytic marker not only exerts bacteriolytic, but also immunomodulatoric properties and was found to bind to the glycosaminoglycan serglycin, an important constituent of the extracellular matrix (ECM). Pathological serum lysozyme levels were described in chronic myeloproliferative disorders (CMPDs) and other hematological conditions. In this context it is remarkable that in polycythemia rubra vera (PV), characterized by a proliferation particularly of the megakaryo- and erythropoiesis, serum lysozyme levels behave independently of the numbers of myelomonocytic cells in peripheral blood. To elucidate whether megakaryopoiesis might be the source of the increased serum lysozyme, we performed an experimental study on isolated and enriched megakaryocytes derived from bone marrow of patients with PV. Findings were compared to a group of patients with reactive (smoker's) polyglobuly (PG). In confirmation of previous results, quantification of serum lysozyme levels showed a slight elevation in the cohort of PV patients which was not correlated with the leukocyte count. Applying an immunohistochemical assay we were able to demonstrate intracytoplasmic lysozyme storage in megakaryocytes. Moreover, performing the reverse hemolytic plaque assay (RHPA), a technique which enables detection of secreted proteins at the single cell level, we found that 54% of the PV, but only 3% of the PG megakaryocytes spontaneously secreted lysozyme. After rhIL-3 treatment the secretion of lysozyme remained unchanged in PV but increased to 14% in PG. These findings suggest that the extent of megakaryocytic lysozyme secretion might discriminate PV from reactive conditions. Although a direct involvement of lysozyme in the regulation of aberrant megakaryopoiesis in PV is not likely, the results of the present study point to the possibility that lysozyme could be involved in the interactions of PV megakaryocytes with ECM. Moreover, the response to rhIL-3 significantly discriminates PV megakaryocytes from megakaryocytes of the PG group.