Bone marrow stroma in idiopathic myelofibrosis and other haematological diseases. An immunohistochemical study

Revisiting Circulating Extracellular Matrix Fragments as Disease Markers in Myelofibrosis and Related Neoplasms

Philadelphia chromosome-negative chronic myeloproliferative neoplasms (MPNs) arise due to acquired somatic driver mutations in stem cells and develop over 10-30 years from the earliest cancer stages (essential thrombocythemia, polycythemia vera) towards the advanced myelofibrosis stage with bone marrow failure. The JAK2V617F mutation is the most prevalent driver mutation. Chronic inflammation is considered to be a major pathogenetic player, both as a trigger of MPN development and as a driver of disease progression. Chronic inflammation in MPNs is characterized by persistent connective tissue remodeling, which leads to organ dysfunction and ultimately, organ failure, due to excessive accumulation of extracellular matrix (ECM). Considering that MPNs are acquired clonal stem cell diseases developing in an inflammatory microenvironment in which the hematopoietic cell populations are progressively replaced by stromal proliferation-"a wound that never heals"-we herein aim to provide a comprehensive review of previous promising research in the field of circulating ECM fragments in the diagnosis, treatment and monitoring of MPNs. We address the rationales and highlight new perspectives for the use of circulating ECM protein fragments as biologically plausible, noninvasive disease markers in the management of MPNs.

Myelofibrosis progression grading based on type I and type III collagen and fibrillin 1 expression boosted by whole slide image analysis

AIMS

The progression of primary myelofibrosis is characterised by ongoing extracellular matrix deposition graded based on 'reticulin' and 'collagen' fibrosis, as revealed by Gomori's silver impregnation. Here we studied the expression of the major extracellular matrix proteins of fibrosis in relation to diagnostic silver grading supported by image analysis.

METHODS AND RESULTS

By using automated immunohistochemistry, in this study we demonstrate that the expression of both types I and III collagens and fibrillin 1 by bone marrow stromal cells can reveal the extracellular matrix scaffolding in line with myelofibrosis progression as classified by silver grading. 'Reticulin' fibrosis indicated by type III collagen expression and 'collagen' fibrosis featured by type I collagen expression were parallel, rather than sequential, events. This is line with the proposed role of type III collagen in regulating type I collagen fibrillogenesis. The uniformly strong fibrillin 1 immune signals offered the best inter-rater agreements and the highest statistical correlations with silver grading of the three markers, which was robustly confirmed by automated whole slide digital image analysis using a machine learning-based algorithm. The progressive up-regulation of fibrillin 1 during myelofibrosis may result from a negative feedback loop as fibrillin microfibrils sequester TGF-β, the major promoter of fibrosis. This can also reduce TGF-β-induced RANKL levels, which would stimulate osteoclastogenesis and thus can support osteosclerosis in advanced myelofibrosis.

CONCLUSIONS

Through the in-situ detection of these extracellular matrix proteins, our results verify the molecular pathobiology of fibrosis during myelofibrosis progression. In particular, fibrillin 1 immunohistochemistry, with or without image analysis, can complement diagnostic silver grading at decent cell morphology.

Serum Biomarkers for Connective Tissue and Basement Membrane Remodeling are Associated with Vertebral Endplate Bone Marrow Lesions as Seen on MRI (Modic Changes)

Vertebral endplate bone marrow lesions, visualized on magnetic resonance imaging (MRI) as Modic changes (MC), are associated with chronic low back pain (cLBP). Since guidelines recommend against routine spinal MRI for cLBP in primary care, MC may be underdiagnosed. Serum biomarkers for MC would allow early diagnosis, inform clinical care decisions, and supplement treatment monitoring. We aimed to discover biomarkers in the blood serum that correlate with MC pathophysiological processes. For this single-site cross-sectional study, we recruited 54 subjects with 38 cLBP patients and 16 volunteers without a history of LBP. All subjects completed an Oswestry Disability Index (ODI) questionnaire and 10-cm Visual Analog Score (VAS) for LBP (VASback) and leg pain. Lumbar T1-weighted and fat-saturated T2-weighted MRI were acquired at 3T and used for MC classification in each endplate. Blood serum was collected on the day of MRI. Biomarkers related to disc resorption and bone marrow fibrosis were analyzed with enzyme-linked immune-absorbent assays. The concentration of biomarkers between no MC and any type of MC (AnyMC), MC1, and MC2 were compared. The Area Under the Curve (AUC) of the Receiver Operating Characteristics were calculated for each biomarker and for bivariable biomarker models. We found that biomarkers related to type III and type IV collagen degradation and formation tended to correlate with the presence of MC (p = 0.060-0.088). The bivariable model with the highest AUC was PRO-C3 + C4M and had a moderate diagnostic value for AnyMC in cLBP patients (AUC = 0.73, specificity = 78.9%, sensitivity = 73.7%). In conclusion, serum biomarkers related to the formation and degradation of type III and type IV collagen, which are key molecules in bone marrow fibrosis, correlated with MC presence. Bone marrow fibrosis may be an important pathophysiological process in MC that should be targeted in larger biomarker and treatment studies.

SOHO State of the Art Updates and Next Questions: Myelofibrosis

The discovery of a mutation in the Janus Kinase 2 gene in 2005 spurred significant progress in the field of myeloproliferative neoplasms. A comprehensive description of genomic factors at play in the malignant clone in myeloproliferative neoplasms, particularly myelofibrosis (MF), have recently led to more precise, personalized prognostic tools. Despite this, understanding of the disease pathogenesis remains relatively limited. We continue to lack a detailed description of the interaction between the hematopoietic stem cell clone, abnormal bone marrow niche cells, and circulating signaling molecules and an understanding of how they cooperate to promote cell proliferation, fibrogenesis, and extramedullary hematopoiesis. Despite our knowledge gaps, recent research in MF has led to promising clinical translation. In this article, we summarize recent insights into MF pathophysiology, progress in the development of novel therapeutics, and opportunities for further advancement of the field.

VCAM-1 expression on bone marrow stromal cells from patients with myelodysplastic syndromes

We studied the expression of VCAM-1 adhesion molecules on stromal cells from the bone marrow of patients with myelodysplastic syndromes, healthy donors, and patients with chronic myeloproliferative diseases and acute leukemias. Expression of adhesion molecule on mesenchymal stromal cells from the bone marrow of patients and healthy donors was evaluated after 2-4 passages by the methods of immunoprecipitation and electrophoresis. VCAM-1 expression in the majority of patients with myelodysplastic syndromes was lower than in healthy donors. At the same time, VCAM-1 expression was not identified on mesenchymal cells from acute leukemia patients. VCAM-1 expression on cells from patients with chronic myeloproliferative diseases did not differ from that in healthy donors. We conclude that VCAM-1 synthesis in bone marrow stromal cells is impaired in patients with myelodysplastic syndromes and acute leukemias. These changes can be followed by the loss of relationships between hemopoietic cells and stromal microenvironment in bone marrow niches. Hemopoietic cells gain the ability for uncontrolled growth, which results in progression of the disease.

Thrombopoietin receptor agonist therapy in primary immune thrombocytopenia is associated with bone marrow hypercellularity and mild reticulin fibrosis but not other stromal abnormalities

Primary immune thrombocytopenia is an acquired autoimmune disorder characterized by platelet count of <100 × 10(9)/l in the absence of other causes of thrombocytopenia. Primary immune thrombocytopenia is defined as 'chronic' when it has been present for more than 12 months without spontaneous remission or maintenance of complete response to therapy. Recently, thrombopoietin receptor agonists became available for treatment of chronic primary immune thrombocytopenia. Anecdotal reports have raised concerns about a possible association between therapy with thrombopoietin receptor agonists and an increase in bone marrow fibrosis. To investigate this association we studied eight patients with primary immune thrombocytopenia in detail comparing fibrosis and other morphological features in pre-therapy and on-therapy bone marrow biopsies, with the longest follow-up reported to date. A slight but significant increase to MF-1 in reticulin fibrosis was observed during therapy, but collagen was never present. On-therapy bone marrows were hypercellular due to panmyelosis with increased trilineage hematopoiesis. Megakaryocytes were increased in number, with acquisition of evident pleomorphism, nuclear hyperlobulation and tendency in some cases to form clusters. The overall picture of the on-therapy marrows was characterized by myeloproliferative neoplasm-like features, resembling essential thrombocythemia or occasionally early primary myelofibrosis. As thrombopoietin receptor agonists are becoming a mainstream treatment for primary immune thrombocytopenia, general pathologists and especially hematopathologists need to be aware of the characteristic morphological changes associated with use of these therapeutic agents, in order to avoid misdiagnosis of a myeloid neoplasm.

The stromal composition of mast cell aggregates in systemic mastocytosis

Systemic mastocytosis is a stem cell disorder characterized histologically by the presence of multifocal compact aggregates of mast cells in at least one extracutaneous organ with or without evidence of skin lesions. The mast cell aggregates are accompanied by fibrosis, which is often significant. However, in spite of its frequent occurrence and severity, little is known about its characteristics. In this study, we evaluated the composition of the fibrotic mast cell aggregates by studying eight bone marrow biopsies and two spleens involved by systemic mastocytosis, and compared the findings with those observed in other fibrotic bone marrow disorders such as primary myelofibrosis and metastatic malignancy. Histochemistry and immunohistochemistry were used to evaluate: (a) extracellular matrix (reticulin, trichrome, collagen IV, laminin); (b) stromal reticulum cells (low-affinity nerve growth factor receptor); (c) presence of myofibroblastic differentiation (smooth muscle actin) and (d) microvessel density (CD34). We found that all cases showed marked reticulin and collagen fibrosis. However, unlike primary myelofibrosis and metastatic malignancy, which are usually associated with increased low-affinity nerve growth factor receptor positivity, its expression was low in all cases of systemic mastocytosis. Myofibroblastic differentiation was only focally detected in two of eight bone marrow biopsies. In all cases, the systemic mastocytosis lesions were largely devoid of type IV collagen and laminin. The latter findings were in contrast with those seen in cases of primary myelofibrosis and metastatic malignancy where smooth muscle actin, collagen IV and laminin were expressed in most cases. Also in contrast with the other two conditions, only minimal vascularity was detectable within the fibrotic mast cell lesions. These findings indicate that systemic mastocytosis exhibits a distinct pattern of stromal change, and suggest that the fibrogenetic mechanism in systemic mastocytosis is most likely different from that of other bone marrow neoplasms which are also associated with fibrosis.

Osteomyelosclerosis with thalassemia trait: report of a rare association, study of platelet function tests and review of literature

Idiopathic myelofibrosis is a chronic myeloproliferative disorder characterized by excessive connective tissue deposition in the bone marrow. It presents with leucoerythroblastic anemia and massive splenomegaly. It is termed osteomyelosclerosis in the presence of primitive bone formation in the bone marrow and radiological presence of osteosclerosis. A 40-year-old male, known case of thalassemia trait presented with fatigue and lump in the abdomen for two months. Physical examination showed splenomegaly 8.5 cm below costal margin. X-ray examination revealed multiple osteosclerotic lesions involving the pelvis and long bones. Hemogram showed: hemoglobin 7.8 gm/dl, TLC 47,500/mm(3); DLC was polymorphs 49%, lymphocytes 7%, eosinophils 4%, basophils 4%, blasts 5%, promyelocytes 2%, myelocytes 14%, metamyelocytes 10%. Platelet count was 60,000/mm(3). Peripheral blood film showed leucoerythroblastic blood picture with features of dysmyelopoiesis. Bone marrow aspiration was diluted with peripheral blood. Bone marrow biopsy showed replacement of marrow by grade III reticulin fibrosis. Bony trabaculae were wide and thick. Platelet function studies were abnormal. The clinical, radiological and hematological features suggested a diagnosis of osteomyelosclerosis. We present this case because no similar association of osteomyelosclerosis with thalassemia trait has been described in English literature to date. This is the first study from India, which describes platelet function tests in a patient with osteomyelosclerosis.

Bone marrow fibrosis: pathophysiology and clinical significance of increased bone marrow stromal fibres

In bone marrow biopsies, stromal structural fibres are detected by reticulin and trichrome stains, routine stains performed on bone marrow biopsy specimens in diagnostic laboratories. Increased reticulin staining (reticulin fibrosis) is associated with many benign and malignant conditions while increased trichrome staining (collagen fibrosis) is particularly prominent in late stages of severe myeloproliferative diseases or following tumour metastasis to the bone marrow. Recent evidence has shown that the amount of bone marrow reticulin staining often exhibits no correlation to disease severity, while the presence of type 1 collagen, as detected by trichrome staining, is often associated with more severe disease and a poorer prognosis. It was originally thought that increases in bone marrow stromal fibres themselves contributed to the haematopoietic abnormalities seen in certain diseases, but recent studies suggest that these increases are a result of underlying cellular abnormalities rather than a cause. A growing body of evidence suggests that increased deposition of bone marrow stromal fibres is mediated by transforming growth factor-beta and other factors elaborated by megakaryocytes, but it is likely that other cells, cytokines and growth factors are also involved. This suggests new avenues for investigation into the pathogenesis of various disorders associated with increased bone marrow stromal fibres.

TGF-beta1 induces bone marrow reticulin fibrosis in hairy cell leukemia

The mechanisms that lead to reticulin fibrosis of bone marrow (BM) in hairy cell leukemia (HCL) are not fully understood. We therefore investigated the involvement of TGF-beta1, a potent fibrogenic cytokine, in this process. Immunoassays revealed that TGF-beta1 is present at higher concentrations in BM, serum, and plasma of HCL patients in comparison with healthy donors (P < 0.001). RT-PCR and immunofluorescence studies showed that TGF-beta1 is overexpressed at the mRNA and protein levels in peripheral blood, spleen, and BM mononuclear cells and that hairy cells (HCs) are the main source of TGF-beta1. Active TGF-beta1 correlated significantly with grades of BM fibrosis, infiltration with HCs, and serum procollagen type III aminoterminal propeptide (PIIINP). Ex vivo studies demonstrated that TGF-beta1 significantly enhances the production and deposition of reticulin and collagen fibers by BM fibroblasts. In addition, BM plasma of HCL patients increased the synthesis of type I and type III procollagens, the main components of reticulin fibers, at the mRNA and protein levels. This fibrogenic activity of BM plasma was abolished by neutralizing anti-TGF-beta1 antibodies. These results show, for the first time to our knowledge, that TGF-beta1 is highly expressed in HCs and is directly involved in the pathogenesis of BM reticulin fibrosis in HCL.

Collagen metabolism and enzymes of the urokinase plasminogen activator system in chronic myeloproliferative disorders: correlation between plasma-soluble urokinase plasminogen activator receptor and serum markers for collagen metabolism

Extracellular proteolytic enzymes of the urokinase-type plasminogen activator (uPA) system and the family of metalloproteinases (MMPs) catalyse the matrix degradation and remodelling processes characteristic of invasive malignant disorders. In a cohort of 50 patients with chronic myeloproliferative disorders (MPD) serum markers for collagen metabolism were compared to plasma levels of enzymes of the uPA and MMP system. Serum aminoterminal propeptide of type III procollagen (S-PIIINP) (P < 0.0001) concentration was significantly higher in the patients (median 3.7 micro g/L vs. 2.5 micro g/L) compared with controls. In a subgroup analysis comprising patients with myelofibrosis (MF), polycythaemia vera (PV) and essential thrombocythaemia (ET), respectively, S-PIIINP levels differed significantly with the highest values found in patients with MF (MF vs. PV vs. ET; P = 0.0027). Serum concentration of carboxyterminal telopeptide of type I collagen (S-ICTP) (P = 0.0006), reflecting type I collagen degradation, was significantly higher in patients compared with controls (median 4.0 micro g/L vs. 2.7 micro g/L). When comparing S-ICTP measurements between patient subgroups and controls there were only significantly higher values among MF and PV patients (MF vs. controls; P < 0.0001, PV vs. controls; P = 0.0016). A significant correlation between the marker for collagen synthesis (S-PIIINP) and degradation (S-ICTP) (r = 0.59; P < 0.0001) was demonstrated. A correlation analysis between serum markers for bone marrow remodelling processes (S-PIIINP, S-ICTP and S-hyaluronan) and plasma-soluble urokinase plasminogen receptor (suPAR) disclosed a significant relationship between suPAR and S-PIIINP (r = 0.48; P = 0.0009), S-hyaluronan (r = 0.56; P < 0.0001) and S-ICTP (r = 0.47; P = 0.0013), respectively. Plasma levels of MMP-2 and -9 were not correlated to serum markers for collagen metabolism. These findings suggest that enzymes of the uPA system might participate in the bone marrow remodelling processes characteristic of MPD.

SU6668 in idiopathic myelofibrosis--a rational therapeutic approach targeting several tyrosine kinases of importance for the myeloproliferation and the development of bone marrow fibrosis and angiogenesis

Idiopathic myelofibrosis is a chronic myeloproliferative disorder being featured by progressive accumulation of connective tissue in concert with marked neovascularization (angiogenesis) of the bone marrow. Both fibrogenesis and angiogenesis are considered to develop consequent to the intramedullary release of various growth-promoting factors from rapidly proliferating and dysplastic megakaryocytes. Among these growth factors are platelet-derived growth factor (PDGF), basic fibroblast growth factor (bFGF), transforming growth factor beta (TGF-beta) and vascular endothelial growth factor (VEGF). The protein kinase inhibitor SU6668 is a potent antiangiogenic inhibitor of receptor tyrosine kinases, including those of VEGFR, PDGFR, bFGFR, and c-kit. The hypothesis is that SU6668 may be an effective agent in the treatment of idiopathic myelofibrosis. This compound has an inhibitory target profile on several tyrosine kinases involved in the myeloproliferation, the development of myeloid metaplasia (bFGFR, PDGFR, VEGFR, and c-kit) and the development of the major stromal changes in the bone marrow - fibrosis and angiogenesis (bFGFR, PDGFR, and VEGFR).

The diagnosis and treatment of hairy-cell leukaemia

The diagnosis of HCL is usually straightforward and is based on the identification of typical HCs in the blood and bone marrow. The suspected diagnosis is confirmed by a combination of TRAP cytochemistry, a distinctive immunophenotype and characteristic BM trephine appearances. Nucleoside treatment is highly effective in inducing prolonged remissions; relapsing patients can usually be successfully retreated with nucleoside. Monoclonal antibody therapy is a promising novel approach to the treatment of resistant disease.

The role of angiogenesis in hematologic malignancies

Several reports have highlighted the biologic relevance of angiogenesis in neoplastic disorders and its potential impact on prognosis. In this review, we focus on recent findings about angiogenesis and angiogenetic factors in hematologic malignancies. We summarize the body of evidence supporting the hypothesis that a common progenitor gives rise to cells of both the endothelial and the hematopoietic lineages, and the current knowledge about the involvement of normal stromal cells in bone marrow angiogenesis. We also discuss the methodological aspects of microvessel count as a measure of tumor angiogenesis. Finally, we describe the current therapeutic role of angiogenesis inhibitors and possible future strategies involving these agents.

Cytokine accumulation in osteitis fibrosa of renal osteodystrophy

Bone marrow fibrosis occurs in association with a number of pathological states. Despite the extensive fibrosis that sometimes characterizes renal osteodystrophy, little is known about the factors that contribute to marrow accumulation of fibrous tissue. Because circulating cytokines are elevated in uremia, possibly in response to elevated parathyroid hormone levels, we have examined bone biopsies from 21 patients with end-stage renal disease and secondary hyperparathyroidism. Bone sections were stained with antibodies to human interleukin-1alpha (IL-1alpha), IL-6, IL-11, tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta) using an undecalcified plastic embedding method. Intense staining for IL-1alpha, IL-6, TNF-alpha and TGF-beta was evident within the fibrotic tissue of the bone marrow while minimal IL-11 was detected. The extent of cytokine deposition corresponded to the severity of fibrosis, suggesting their possible involvement in the local regulation of the fibrotic response. Because immunoreactive TGF-beta and IL-6 were also detected in osteoblasts and osteocytes, we conclude that selective cytokine accumulation may have a role in modulating bone and marrow cell function in parathyroid-mediated uremic bone disease.

Basement membrane of mouse bone marrow sinusoids shows distinctive structure and proteoglycan composition: a high resolution ultrastructural study

Venous sinusoids in bone marrow are the site of a large-scale traffic of cells between the extravascular hemopoietic compartment and the blood stream. The wall of the sinusoids consists solely of a basement membrane interposed between a layer of endothelial cells and an incomplete covering of adventitial cells. To examine its possible structural specialization, the basement membrane of bone marrow sinusoids has now been examined by high resolution electron microscopy of perfusion-fixed mouse bone marrow. The basement membrane layer was discontinuous, consisting of irregular masses of amorphous material within a uniform 60-nm-wide space between apposing endothelial cells and adventitial cell processes. At maximal magnifications, the material was resolved as a random arrangement of components lacking the "cord network" formation seen in basement membranes elsewhere. Individual components exhibited distinctive ultrastructural features whose molecular identity has previously been established. By these morphological criteria, the basement membrane contained unusually abundant chondroitin sulfate proteoglycan (CSPG) revealed by 3-nm-wide "double tracks," and moderate amounts of both laminin as dense irregular coils and type IV collagen as 1-1.5-nm-wide filaments, together with less conspicuous amounts of amyloid P forming pentagonal frames. In contrast, 4.5-5-nm-wide "double tracks" characteristic of heparan sulfate proteoglycan (HSPG) were absent. The findings demonstrate that, in comparison with "typical" basement membranes in other tissues, the bone marrow sinusoidal basement membrane is uniquely specialized in several respects. Its discontinuous nature, lack of network organization, and absence of HSPG, a molecule that normally helps to maintain membrane integrity, may facilitate disassembly and reassembly of basement membrane material in concert with movements of adventitial cell processes as maturing hemopoietic cells pass through the sinusoidal wall: the exceptionally large quantity of CSPG may represent a reservoir of CD44 receptor for use in hemopoiesis.

Erythromegakaryocytic cells synthesize laminin-8 (alpha4beta1gamma1)

Blood platelets contain laminin-8 (alpha4beta1gamma1), a recently described laminin isoform, but the origin of platelet laminin is at present unknown. Laminin of platelets could be synthesized by megakaryocytes or, alternatively, endocytosed from plasma or other sources. In the present study, the synthesis and presence of laminin-8 in erythromegakaryocytic HEL and DAMI cells were explored. In HEL cells, transcripts for alpha4, beta1, and gamma1 laminin chains were readily detected by RT-PCR. Immunofluorescence flow cytometry demonstrated reactivity of mAbs to laminin beta1 and gamma1 chains with permeabilized cells. Metabolic labeling of HEL cells using [(35)S]methionine and [(35)S]cysteine followed by immunoprecipitation with monoclonal antibodies to beta1 and gamma1 chains revealed bands of approximately 220 and 200 kDa. In the HEL cell lysate, polypeptides of 220 and 200 kDa were recognized by monoclonal antibodies to laminin beta1 and gamma1 chains, respectively, whereas immunoaffinity-purified rabbit antibodies to laminin alpha4 chain gave inconclusive results. However, following immunoaffinity purification on a laminin beta1 antibody-Sepharose column, a 200-kDa band was readily detected by the antibodies to laminin alpha4 chain. Similar results were obtained with DAMI cells. The size of laminin chains of HEL/DAMI cells was similar, though not identical, to the one of platelets, and the alpha4 chain was noncovalently associated to disulfide-bonded beta1gamma1 heterodimer, as in platelets. We conclude that erythromegakaryocytic cells synthesize laminin-8.

Clinicopathological impact of the interaction between megakaryocytes and myeloid stroma in chronic myeloproliferative disorders: a concise update

In this report an attempt has been made to discuss some of the issues pertinent to myelofibrosis complicating chronic myeloproliferative disorders (CMPDs) that are significantly associated with megakaryocyte function. In this context, biochemical, clinical and particularly morphological features were reviewed. Morphological findings based on elaborate techniques were in keeping with the assumption that in chronic myeloid leukemia (1) the number of CD61-positive megakaryocytes, and in particular their precursors were the parameters most closely associated with myelofibrosis (2) an increased content of reticulin fibers in follow-up biopsies significantly correlated with laboratory data indicative of a high tumor burden (anemia, peripheral blasts, hepatosplenomegaly) and thus a more advanced stage of the disease process (3) even a slight increase in reticulin, i.e. doubling of the normal fiber density was associated with a worse prognosis independent of therapeutic regimens given (4) Dynamics of myelofibrosis was significantly influenced by treatment. In this context, calculation of the myelofibrosis progression index (MPI) revealed a higher score following interferon therapy compared with busulfan. In addition, in idiopathic myelofibrosis (5) the evolution of myelofibrosis was unpredictable and according to the MPI, progression occurred at a relatively low rate (6) proliferation and dilatation of sinusoids accompanying intravascular hematopoiesis and collagen type IV deposits were predominant features in later (fibro-osteosclerotic) stages in the course of disease (7) transmural migration of megakaryocytes demonstrated by three dimensional reconstruction revealed a mole-like tunneling through the thickened sinusoidal wall. A very careful assessment of the numerous correlations between bone marrow features and laboratory data will allow clinicians and pathologists to gain a better insight into the mutual relationships between hematological and morphological findings in CMPDs.

Integrin receptors and hairy cell leukaemia

The ability of a cell to recognize and specifically localise within an appropriate tissue environment is essential to the proliferation and survival of that cell. The integrin family of cell-surface adhesion-receptors are essential to such tissue localisation, allowing a migrating cell to specifically recognise, localise within-, and respond to- the cellular or extracellular matrix ligands that characterise a given tissue. We have investigated how the expression and activity of integrin receptors underlies the consistent and unusual tissue distribution of the malignant B lymphocytes of hairy cell leukaemia (HCL). In this report we review our published work in this area. Our findings are then discussed within the context of current knowledge of integrin receptors and their ligands, and in relation to the clinical features of HCL.

Actions of molecules which regulate hemopoiesis on endothelial cells: memoirs of common ancestors?

The proliferation and differentiation of hematopoietic stem cells (hematopoiesis) takes place in close contact with stromal cells and matrix in bone marrow. Hematopoiesis requires cytokines, collectively termed colony stimulating factors (CSFs), which act on progenitor cell populations and induce their commitment to a specific lineage. For instance, leukemia, inhibitor factor and stem cell factor act on pluripotent cells and immature progenitors, granulocyte-macrophage colony stimulating factor (GM-CSF) acts at early stages of the development of myelomonocytic lineage, whereas granulocyte-colony stimulating factor (G-CSF) and macrophage-colony stimulating factor (M-CSF) act on more mature cells of the same lineage and are only required later during the differentiation of this cell lineage. A second important element for the hematopoietic process is the presence of extracellular matrix proteins, which bind CSFs and correctly present the molecules to specific receptors present on the surface of the progenitor cells. Finally, stromal cells (i.e. fibroblasts, endothelial cells and adipocytes) which support the growth of hematopoietic stem cells in vitro, are crucial for the production of CSFs and protein matrix and regulate the passage of mature cells from bone marrow to bloodstream. Idiopathic myelofibrosis is an example of the relevance of microenvironment in hematopoiesis. This disease is characterized by fibroblast and basement membrane accumulation, appearance of myofibroblasts and modification of the capillary network and provokes a bone marrow aplasia. In this article we review recent studies on the role of hemopoietic cytokines on stromal cells, in particular on endothelial cells, and propose a double role for CSFs in hematopoiesis: to induce the commitment of progenitor cells and to maintain the behavior of bone marrow endothelial cells.

Serum laminin P1 in idiopathic myelofibrosis and related diseases

The serum concentration of laminin P1 antigen was determined in 32 patients with various myeloproliferative disorders, including 19 patients with idiopathic myelofibrosis. The serum concentration of the aminoterminal propeptide of type III procollagen (PIIINP) was measured concomitantly in 27 patients. Serial laminin measurements were carried out in 25 patients. The median serum laminin concentration in patients with acute disease, i.e. acute myelofibrosis and patients in a transforming disease phase was significantly higher (1.58 U/ml; range 1.15-2.07) as compared with patients with chronic disease (1.02 U/ml; range 0.75-1.76; p = 0.012) and healthy control subjects (1.13 U/ml; range 0.75-1.67; p = 0.00015). In individual patients serum laminin covariated closely with serum PIIINP, the leucocyte count and LDH. The median serum laminin concentration in patients with a huge spleen was significantly lower than in the patient group with a normal spleen size/previous splenectomy. Pronounced splenomegaly was particularly prevalent in patients with chronic disease implicating splenic enlargement as a significant extrahepatic site of laminin uptake/degradation in myeloproliferative disorders.

Idiopathic myelofibrosis--an update with particular reference to clinical aspects and prognosis

Idiopathic myelofibrosis (IMF) is characterized by excessive accumulation of connective tissue in the bone marrow as part of a clinical syndrome which in its classical form is featured by leukoerythroblastic anemia and huge splenomegaly at the time of diagnosis. An acute variant of the disease exists being featured by pancytopenia, nor or minimal splenomegaly and a rapidly fatal clinical course. This review describes the relationship of IMF to other chronic myeloproliferative disorders and highlights current concepts of the pathogenesis of bone marrow fibrosis, implicating the intramedullary release of various growth factors, including platelet-derived growth factor beta. In a subgroup of patients bone marrow fibrosis may develop consequent to autoimmune bone marrow damage. The clinical and laboratory findings in some of the larger series of patients are presented and the reasons for the highly variable clinical presentation and prognosis are critically discussed. It is proposed that studies on prognosis in IMF are based upon simple prognostic staging systems, which should include the Hb-concentration, platelet count, spleen size and the presence/absence of osteomyelosclerosis on X-ray. Using these parameters the patients are easily categorized into three prognostic groups with highly different survival times.

Recent developments in the cell biology of granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor: activities on endothelial cells

Granulocyte-macrophage colony-stimulating factor and granulocyte colony-stimulating factor were considered as growth and differentiation factors restricted to hematopoietic cells. It was recently found that non-hematopoietic cells, including endothelial cells, respond to these cytokines. In this review we describe their effects on endothelial cells, underlining their role in the behavior and survival of the microenvironment of bone marrow, in the angiogenesis process related to the progression of solid tumors and of vascular tumors, and in the homing of lymphocytes.

Characterization of an acute micromegakaryocytic leukaemia: evidence for the pathogenesis of myelofibrosis

The current hypothesis for the pathogenesis of myelofibrosis involves the intramedullary release of growth factors from defective or abnormal megakaryocytes. We describe a case of an acute micromegakaryocytic leukaemia, in a patient with chronic myelofibrosis, that provides additional evidence for this concept. The micromegakaryocytes, which reached 223 x 10(9)/l, were characterized morphologically by both light and electron microscopy, immunocytochemically and by platelet peroxidase activity. The cells were shown to have a mature cytoplasm, containing alpha granules and the associated proteins; vWF:Ag, fibrinogen, fibronectin and protein S. DNA analysis, by both a Seescan Solitaire Plus image analysis system and flow cytometry, revealed nuclear immaturity, with 92% of cells being diploid. Serum markers of connective tissue synthesis, namely carboxy terminal peptide of procollagen I (PICP), procollagen terminal peptide III (PIIIP) and laminin all increased significantly following transformation and were associated with an increase in platelet-derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta). These observations support the current hypothesis for bone marrow fibrosis formation and provide, for the first time, a link between in vivo growth factor release, bone marrow stromal turnover and megakaryocyte mass. In addition, the release of biologically active TGF-beta may explain both the increased fibronectin and angiogenesis characteristic of myelofibrotic bone marrow.

Macrophages in normal human bone marrow and in chronic myeloproliferative disorders: an immunohistochemical and morphometric study by a new monoclonal antibody (PG-M1) on trephine biopsies

An immunohistochemical and morphometric study was performed on routinely processed trephine biopsies of the bone marrow in 30 normal individuals and in 90 patients with various subtypes of chronic myeloproliferative disorder. Using a new monoclonal antibody (PG-M1) directed against a formalin-resistant epitope on macrophages and by employment of the Prussian blue reaction, quantitation of this cell population was feasible. Morphometric analysis revealed that the number of iron-laden macrophages represented only a fraction of the total number of histiocytic reticular cells. As could be expected, in polycythaemia rubra vera, no haemosiderin deposits were detectable, but the content of macrophages slightly exceeded that of the normal bone marrow. In chronic myeloid leukaemia 9 of 30 patients showed a significant increase in PG-M1-positive reticular cell elements. These were consistent with pseudo-Gaucher cells, sea-blue histiocytes and intermediate cell types. Primary (idiopathic) myelofibrosis-osteomyelosclerosis was characterized by a significant increase in macrophages (25 of 30 patients). Involvement of macrophages in the complex mechanisms generating bone marrow fibrosis and angiogenesis and in bone remodelling (osteosclerosis) may be responsible for this finding.