Platelet-derived growth factor(s) mitogenic activity in patients with myeloproliferative disease

Variation of PDGF, TGFbeta, and bFGF levels in essential thrombocythemia patients treated with anagrelide

We studied 15 patients with essential thrombocythemia (ET) before treatment and after normalization of platelet count by anagrelide. Significantly increased plasma levels of PDGF, TGFbeta, and bFGF were found. Patients with mild reticulin fibrosis in bone marrow had higher PDGF levels. During treatment, plasma TGFbeta and bFGF levels remained elevated in most patients (P < 0.0001 and P < 0.01, respectively). Intraplatelet PDGF levels were low before treatment (P < 0.006) and normal on hematological remission, without relation with the presence or absence of reticulin fibrosis in bone marrow. Intraplatelet TGFbeta levels were normal regardless of the platelet count. Intraplatelet bFGF levels were raised before (P < 0.001) and during treatment (P < 0.01). By immunostaining, TGFbeta and bFGF were seen in megakaryocytes and lymphocytes with a similar pattern of intensity in patients and controls, suggesting that other cells might also contribute to the raised plasma values. We believe that the plasma increment of these cytokines suggests that they play a role in the pathogenesis of ET. The normal PDGF plasma level found during treatment may be in relation with the platelet count. However, the persistent increase of TGF-beta in plasma and bFGF both in plasma and platelets may indicate dysregulation of cytokine synthesis in TE.

Development of Dermatomyositis in a Patient with Primary Myelofibrosis

It is known that immunologic mechanisms play an important role in the disease process of some patients with idiopathic myelofibrosis. Patients with idiopathic myelofibrosis have an increased incidence of autoantibodies and circulating immune complexes. Dermatomyositis is a disorder of unknown cause, but immune-mediated muscle damage is believed to be important as a pathogenic mechanism. We have a patient who had idiopathic myelofibrosis and developed dermatomyositis during the disease course, a previously unreported combination. Increasing clinicians' awareness of both myelofibrosis and dermatomyositis may provide further insight into a possible relationship of the two conditions.

Expression of c-myb and B-myb oncogenes on myelofibrotic marrow fibroblasts

The term IMF (Idiopathic Myelofibrosis) refers to a primary bone marrow disease in which the normal haematopoietic bone marrow cells are for unknown reasons replaced by connective tissue. The pathogenesis of the disease has not been clarified yet. We have speculated that the increment of proliferation of bone marrow fibroblasts in IMF may be the consequence of the over-expression of some oncogenes, leading or contributing to the fibrosis via a cell amplification. Thus, we investigated the possible role of the c-myb and B-myb genes in IMF and control bone marrow fibroblasts in different culture conditions to evaluate proliferation parameters in the absence or presence of serum. Using the reverse transcriptase polymerase chain reaction technique, we demonstrated that the kinetics of induction was similar for both c-myb and B-myb during the proliferation of normal bone marrow fibroblasts. When compared to normal controls, cultured IMF fibroblasts showed more elevated values of c-myb and B-myb RNA; furthermore, after a 72 hours stimulation with serum, c-myb and B-myb messages remained relatively high in myelofibrotic fibroblasts. Finally, after serum starvation, c-myb and to a lesser extent B-myb RNA levels remained unusually high in IMF fibroblasts, while under the same experimental conditions c-myb and B-myb messages became virtually undetectable in normal bone marrow fibroblasts. To our knowledge this work represents the first description of an abnormal behavior of these genes in IMF fibroblasts.

Pathogenesis and management of idiopathic myelofibrosis

Idiopathic myelofibrosis is the least common and carries the worst prognosis of the chronic myeloproliferative disorders. The primary disease process is a clonal haematopoietic stem cell disorder which results in a chronic myeloproliferation and an atypical megakaryocyte hyperplasia. In contrast, the characteristic stromal proliferation is a reactive phenomenon, resulting from the inappropriate release of megakaryocyte/platelet-derived growth factors, including PDGF, TGF-beta bFGF and calmodulin. The median survival is approximately 4 years, although individual survival varies greatly. A variety of prognostic schema have been developed which enable the identification of high-risk patients, for whom bone marrow transplantation should be considered. Management for the majority of patients, however, is directed towards the alleviation of symptoms and improvement in quality of life. This review summarizes the recent advances in our understanding of the disease's pathogenesis and discusses the limited therapeutic options available to clinicians.

Pediatric hyperfibrotic myelodysplasia: an unusual clinicopathologic entity

This study is presented to highlight a rare pediatric bone marrow pathology in which features of bone marrow dysplasia coexist with severe fibrosis in a clinical setting of fever, anemia, and organomegaly. Fourteen children (nine males, five females) clinically presented with fever, anemia, and hepatosplenomegaly. Extensive bone marrow fibrosis with dysplastic features was seen in their marrow precursor cells. Peripheral blood smears showed teardrop poikilocytes thrombocytopenia, and occasional blasts. In conclusion, pediatric hyperfibrotic myelodysplasia is a distinct clinicopathologic entity. Myeloproliferative and dysmyelopoietic syndromes are complex disorders that are interrelated and not always easily diagnosed only on morphologic grounds.

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.

Megakaryocytes and fibroblasts--interactions as determined in normal human bone marrow specimens

An in vitro study was performed to investigate possible interactions between megakaryocytes and bone marrow fibroblasts, both obtained from healthy donors. We were able to demonstrate that the proliferation of fibroblasts increased significantly by co-culturing these cells with megakaryocytes for 6 days. Addition of neutralizing antibodies for PDGF and TGF beta 1, caused a significant reduction of fibroblast growth. Inhibition of cell to cell contacts via tissue culture inserts generated a conspicuous impairment of fibroblast proliferation compared with megakaryocyte-fibroblast co-cultures, where contact was allowed. Hence, our findings suggest that a close spatial relationship between megakaryocytes and fibroblasts is needed for the activation of growth in normal human bone marrow. Neighbouring of megakaryocytes and fibroblasts seems to be necessary in order to achieve a certain threshold of local growth factor concentration. Our results are in keeping with the assumption that PDGF and TGF beta 1, are secreted by normal human megakaryocytes in very low concentrations and promote significantly fibroblast proliferation.

Influence of cytokines (IL-1 alpha, IL-3, IL-11, GM-CSF) on megakaryocyte-fibroblast interactions in normal human bone marrow

The evolution of myelofibrosis accompanying chronic myeloproliferative disorders (CMPDs) is often linked with megakaryopoiesis. However, it is not known whether or to what extent megakaryocytes of normal human bone marrow are capable of stimulating fibroblast growth. For this reason, an in vitro study was performed to elucidate possible cytokine-dependent interactions between megakaryocytes and fibroblasts derived from healthy volunteers. Fibroblast growth was significantly promoted by the presence of megakaryocytes and modulated by additional application of various cytokines. While recombinant human (rh) interleukin (IL)-1 alpha had no obvious effect on fibroblast proliferation, a slight increase was detected on adding granulocyte-macrophage colony stimulating factor (rhGM-CSF). Application of rhIL-3 caused a significant increase in the number of fibroblasts. In contrast, administration of rhIL-11 suppressed the megakaryocyte-dependent growth-promoting effect and co-stimulation with rhIL-3 led to a significant decrease of fibroblast number in comparison to rhIL-3-stimulated co-cultures. Inhibition of cell-cell contact in unstimulated, as well as in rhIL-3-stimulated co-cultured led to a conspicuous impairment of fibroblast growth. A similar effect was observed when neutralizing antibodies directed against platelet-derived growth factor (PDGF) and transforming growth factor (TGF)beta 1 were added to rhIL-3-stimulated cultures. Our findings are in keeping with the assumption that interactions between megakaryocytes and fibroblasts involve in cytokine-mediated functional network regulated by factors such as spatial relationship, cytokine stimulation, and low concentrations of mediators, particularly PDGF and TGF beta. In this complex system rhIL-3 seems to play a crucial role in the promotion of these various interrelationships.

The impact of interferon versus busulfan therapy on the reticulin stain-measured fibrosis in CML--a comparative morphometric study on sequential trephine biopsies

To evaluate treatment-related changes of the reticulin stain-measured fibrosis in Ph(1+)-CML, a clinicopathological study was performed on sequential trephine biopsies of the bone marrow following either interferon (IFN) or busulfan (BU) monotherapy. Using the monoclonal antibody CD61 for the identification of megakaryopoiesis and Gomori's silver impregnation method, number of megakaryocytes and density of argyrophilic (reticulin and collagen) fibers were determined by morphometry. We studied specimens from 26 patients with IFN-alpha 2b (including nine patients with additional IFN gamma) therapy and from 23 patients who had received BU. In both groups, repeated bone marrow biopsies (total 125) revealed a significant increase in the fiber content, as well as in the number of megakaryocytes during treatment. To assess the dynamics of myelofibrosis more precisely, computation of differences in the degree of fiber density between the first and last examination was carried out. Regarding the considerable variations in the biopsy intervals, a so-called myelofibrosis progression index (MPI) was calculated. Following this rationale, we were able to demonstrate that, in comparison to the BU-group, speed of progression of bone marrow fibrosis was significantly increased in CML patients treated with IFN. Preliminary statistical analysis indicated a relationship between myelofibrosis on admission, which was always associated with increased growth of megakaryocytes, and the MPI with survival. Even when these parameters were regarded, prognosis was significantly more favorable in the IFN-treated patients. The failure of IFN and BU to inhibit the evolution of myelofibrosis may be related to several conversely acting pathomechanisms. Among others, the inability of both therapeutic agents to reduce the number of megakaryocytes more effectively should be taken into consideration.

Trisomy 14, deletion 20q and t(3;3) (q21;q26) in a case of myelodysplastic syndrome with myelofibrosis

We describe a patient with trilineage myelodysplasia and hyperplastic megakaryopoiesis associated with significant myelofibrosis at diagnosis, who developed acute myeloid leukaemia two months afterwards. The clinical and pathological features were consistent with a myelodysplasia/myelofibrosis syndrome with leukemic transformation. Cytogenetic investigation showed trisomy 14, del(20q) and t(3;3) (q21;q26). These findings are of possible significance in the understanding of the association between myelodysplasia and myelofibrosis.

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.

Splenic haematopoiesis in primary (idiopathic) osteomyelofibrosis: immunohistochemical and morphometric evaluation of proliferative activity of erytro- and endoreduplicative capacity of megakaryopoiesis (PCNA- and Ki-67 staining)

Using monoclonal antibodies against proliferating cell nuclear antigen or PCNA (PC10) and the Ki-67 antigen (MIB1), an immunohistochemical and morphometric study was performed on routinely processed splenic tissue from ten patients with primary (idiopathic) osteomyelofibrosis (OMF). To determine the proliferation capacity of erythroid precursors and the endoreduplicative activity of megakaryocytes, corresponding antibodies (Ret40f and CD61) were applied in combination with the cell-cycle markers (sequential double-immunostaining). Morphometric analysis revealed no significant differences in PCNA or Ki-67 reactivity in either cell lineages. In comparison with previous studies on normal bone marrow, in splenic tissue showing myeloid metaplasia, the numbers of PCNA-labelled proerythroblasts, erythroblasts and megakaryocytes were conspicuously increased. Considering the ineffective erythropoiesis in OMF, there seemed to be a disproportional enhancement in PCNA and Ki-67 immunostaining of the red cell lineage. Similarly, the small size of megakaryocytes in advanced, OMF-associated myeloid metaplasia was in keeping with an impairment of endoreduplicative activity. In addition to various other contributory factors, anaemia in OMF may be partially caused by secondary folate (haematinic) deficiency. From experimental studies this defect is known to cause an abnormal arrest in the S-phase of the cell-cycle, comparable to that characterising pernicious anaemia. As a sequel of this pathomechanism, an undue overexpression of PCNA and Ki-67 has to be assumed, that is not necessarily associated with DNA synthesis or cell cycling.

Macrophages (phagocytic-histiocytic reticular cells) in reactive-inflammatory lesions of the bone marrow and in myelodysplastic syndromes (MDS). An immunohistochemical and morphometric study by use of a new monoclonal antibody (PG-M1)

An immunohistochemical and morphometric study was performed on trephine biopsies of the bone marrow in 52 patients (28 males/24 females; age 68 years) with various subtypes of myelodysplastic syndromes (MDS) to determine the number of macrophages (phagocytic-histiocytic reticular cells). Quantifications included the haemosiderin-storing subpopulation (Prussian-blue reaction) of this lineage as well as the iron-free compartment. The latter was identified by a new monoclonal antibody (PG-M1) which is specifically directed against histiocytic reticular cells. Bone marrow specimens of individuals without haematological disorders and those showing reactive lesions served as controls. In comparison with the normal bone marrow and inflammatory changes (i.e. rheumatoid arthritis) 23 of the 52 patients with MDS revealed a significant increase in macrophages. This increase encompassed not only the iron-laden subpopulation but also the total number of phagocytic reticular cells. Accumulation of macrophages in MDS was speculated to be due to a premature and enforced degradation of dysplastic cell elements leading to phagocytosis of haemosiderin and debris material. Moreover, cells of the monocyte-macrophage system could be involved in the complex pathomechanism of fibrillogenesis, since in a considerable percentage of patients with MDS, an increase in reticulin (argyrophilic) fibres was noticeable. Our finding of an expansion of the macrophage compartment in about half of the patients with MDS is in keeping with results of cell culture studies on colony formation of granulocyte-macrophage precursors (CFU-GM).

Platelet-derived growth factor (PDGF) in plasma of breast cancer patients: correlation with stage and rate of progression

Plasma levels of platelet-derived growth factor (PDGF) were measured in 58 female patients with breast cancer and in 9 normal female control subjects by means of a specific radioimmunoassay. Levels in normal control subjects were all below the lower limits of detection by the assay (1.56 fmol/100 microliters plasma). Two of 17 (12%) patients with stage 2 breast cancer had detectable plasma levels. Among patients with Stage 4 breast cancer 13/41 (32%) had significantly elevated levels (greater than 2 times the lower limit of sensitivity of the assay). Patients with elevated PDGF levels had a significantly greater degree of metastatic involvement and significantly shorter survival. Apart from being a marker of aggressive high bulk breast cancer, PDGF may be involved in the acceleration of growth of some metastatic breast tumors.

Idiopathic myelofibrosis: historical review, diagnosis and management

Idiopathic myelofibrosis is reviewed from several aspects. The historical development of knowledge about this disorder is discussed, from early descriptions of extramedullary hematopoiesis associated with numerous etiologies, a debate over pathogenetic mechanisms, followed by newer evidence which placed this disorder with the myeloproliferative disorders. Evidence is presented showing that idiopathic myelofibrosis is an acquired clonal disorder in terms of the hematopoietic abnormalities, but that the marrow fibrosis is a result of non-clonal disordered fibrogenesis. The clinical, laboratory and pathologic features of idiopathic myelofibrosis are discussed. The features which distinguish this disorder from the other myeloproliferative disorders, particularly chronic myelogenous leukemia are emphasized. The natural history is described together with an evaluation of accepted and experimental therapy.

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

Bone marrow stroma was investigated immunohistochemically in 31 patients with haematological diseases, mainly idiopathic myelofibrosis (n = 8) and related chronic myeloproliferative disorders (n = 14). The bone marrow from patients with idiopathic myelofibrosis and some CML patients showed marked staining reactions with antibodies against type III procollagen (pN collagen), type IV collagen, fragment P1 of laminin and factor VIII. Patients with osteomyelosclerosis had particularly increased collagen content, including both newly deposited type III collagen (pN collagen) and mature collagen fibres. As in normal bone marrow, argyrophilic fibres and type III collagen displayed a close co-distribution, which was also demonstrated for type IV collagen and laminin. While normal bone marrow sinusoids had discontinuous basement membranes, fibrosing bone marrow was characterized by endothelial cell proliferation and capillarization, with the development of continuous sheets of basement membrane material beneath endothelial cells.

Increased intraplatelet levels of platelet-derived growth factor and transforming growth factor-beta in patients with myelofibrosis with myeloid metaplasia

Platelet-derived growth factor (PDGF) is thought to play some role in the genesis of fibrosis associated with myeloproliferative disorders. In addition, transforming growth factor-beta (TGF-beta) has been confirmed to promote fibrotic process. Both PDGF and TGF-beta have been shown to cooperate with epidermal growth factor (EGF) in regulating the growth of human marrow fibroblasts. All three are contained in platelet alpha-granules. We report the results of a study in patients with myelofibrosis with myeloid metaplasia (MMM). We evaluated PDGF, TGF-beta and EGF-like activities in circulating platelets from patients compared to healthy subjects. In contrast to EGF-like intraplatelet levels which were similar in patients and in normal donors (1-4 ng/10(9) platelets), we found constantly higher values for both PDGF and TGF-beta in MMM patients. In both radioimmunoassay (RIA) and assay for mitogenic activity on human bone marrow fibroblasts, PDGF levels were increased on the average 2-3.5-fold over the levels found in normal donors (P less than 0.01 and P less than 0.001, respectively). PDGF serum levels in patients were consistent with those found in platelets. In platelet-poor plasma (PPP), PDGF concentrations were undetectable or congruent to 2 ng/ml in patients and in control donors as well. The total TGF-beta activity in platelet lysates, determined using a competitive radioreceptor binding assay on Swiss 3T3 mouse cells and an inhibition growth assay on CCL64 cells, was found 2-3-fold increased in patients with MMM as compared to control subjects (P less than 0.003). These results emphasize that, not only PDGF, but also TGF-beta are implicated in the myelofibrosis with myeloid metaplasia.

Platelet derived growth factor messenger RNA is increased in bone marrow megakaryocytes in patients with myeloproliferative disorders

Platelet derived growth factor (PDGF) has been suggested to play an important role in the pathogenesis of myelofibrosis, which often occurs in patients with myeloproliferative disorders (MPD). We examined the expression level of PDGF mRNA in bone marrow megakaryocytes from 13 MPD patients by in situ hybridization, using cDNA probes for both human PDGF A chain and B chain (c-sis). The mRNA level for both chains in the patients was significantly higher than that in control patients, and was markedly higher for one patient with essential thrombocythemia and one with polycythemia vera. Transcripts for A chain and B chain were expressed with a positive correlation in the MPD patients. Using the marrow fibroblast proliferation assay, we found PDGF activity in purified megakaryocytes from one of the MPD patients with high mRNA level to be similar to that from one control patient. In addition, PDGF was previously shown to be decreased in circulating platelets from MPD patients. These results may suggest that, in some patients, PDGF is synthesized in megakaryocytes at a high rate, but some fraction is released into the bone marrow environment, if the level of PDGF mRNA is assumed to be linearly related to the protein synthesized. This might be one possible mechanism causing marrow fibrosis in MPD patients.

Myelofibrosis: a review of clinical and pathologic features and treatment

The purpose of this review is to discuss and clarify the current understanding of the pathogenesis, clinical manifestations, and treatment of MF. MF may be either a primary or secondary disorder. It is characterized by an increased deposition of bone marrow collagen, fibronectin, and laminin. Present evidence indicates that MF may be mediated by platelet or megakaryocyte growth factors, decreased prostaglandin mediated stem cell inhibition, immune complex deposition, and both fibroblast and endothelial cell proliferation. Recently acute MF has been recognized to be identical to acute megakaryocytic leukemia. Secondary MF usually responds to appropriate treatment of the underlying disease. Primary MF is usually treated by blood product support, but may be responsive to androgens, splenectomy, splenic irradiation, chemotherapy, or bone marrow ablation with marrow reconstitution.

Transforming growth factor-beta regulates growth as well as collagen and fibronectin synthesis of human marrow fibroblasts

Three growth factors present in platelets, namely platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-beta) and epidermal growth factor (EGF), have been implicated in the pathogenesis of bone marrow fibrosis frequently associated with myeloproliferative disorders. In this study, regulation of the proliferation, as well as collagen and fibronectin synthesis from marrow fibroblasts by TGF-beta was investigated. TGF-beta alone at high plating density stimulated the proliferation of cells at low concentrations, but rather showed inhibition at high concentrations in both MPD patients and control subjects. In the presence of PDGF, which has been confirmed to be a main growth factor for marrow fibroblasts, low concentration of TGF-beta inhibited the proliferation at low cell density, but there was no inhibition at high cell density. The synthesis of both type I and type III procollagen was enhanced by high concentrations of TGF-beta in both MPD patients and control subjects, while PDGF or EGF showed no effect. The fibronectin synthesis was also enhanced by TGF-beta, but not by PDGF or EGF. These results suggest that growth and stromal protein synthesis of fibroblasts causing marrow fibrosis are regulated by TGF-beta as well as PDGF and EGF, when these factors are released or leaked from platelets or megakaryocytes into marrow environment in MPD patients.

Myelofibrosis: a concise review of clinical and pathologic features and treatment

This paper reviews and clarifies the current understanding of the clinical and pathologic features and treatment of MF. Recent investigations indicate that MF may be mediated by platelet- and megakaryocyte-derived growth factors, impaired prostaglandin-mediated stem cell growth inhibition, or excessive endothelial cell and fibroblast proliferation. Immunologic disorders have been associated with MF. MF may be either a primary or a secondary phenomenon. Secondary MF often regresses with appropriate treatment of this underlying disorder. Primary MF may require androgen therapy, splenectomy, splenic irradiation, bone curettage, chemotherapy, or bone marrow transplantation.

A reversible defect of platelet PDGF content in myeloproliferative disorders

Platelet PDGF (platelet derived growth factor), platelet associated IgG and plasma levels of circulating immune complexes were measured in patients with chronic myeloproliferative disorders (primary myelofibrosis, primary proliferative polycythaemia and essential thrombocythaemia). Platelet PDGF was low in 11/12 patients, immune complexes were elevated in 11/16, and PlAIgG was elevated in all 14 patients in whom it was measured. There was no significant correlation between platelet PDGF and plasma levels of immune complexes (r = -0.5, P greater than 0.1). Treatment with busulphan and prednisolone for 2-3 months restored normal levels of platelet PDGF and suppressed plasma immune complex levels. Plasmapheresis lowered levels of immune complexes but had no effect on platelet PDGF. These results indicate that the low platelet PDGF levels in chronic myeloproliferative disorders represent a reversible defect which is not directly related to the presence of immune complexes.

Marrow fibroblasts from patients with myeloproliferative disorders show increased sensitivity to human serum mitogens

The growth of marrow fibroblasts from patients with myeloproliferative disorders (MPD) was investigated using platelet derived growth factor (PDGF) and human serum as mitogens in the presence of human plasma derived serum. The proliferation of fibroblasts in MPD patients was increased compared to normal individuals, especially in patients with chronic myelocytic leukaemia and essential thrombocythaemia. This increment of proliferation might be due to higher sensitivity of the fibroblasts to plasma derived serum than to PDGF, because the ratio of proliferation with PDGF to that without PDGF, when compared between patients and normals, remained unchanged. These results suggest that MPD fibroblasts are more sensitive to some factor(s) in plasma, and this fact could partially explain the pathogenesis of myelofibrosis in MPD patients.

Effects of platelet derived growth factor, epidermal growth factor and transforming growth factor-beta on the growth of human marrow fibroblasts

The effects of three growth factors contained in platelets on human bone marrow fibroblasts as well as fibroblast colony-forming cells were investigated to clarify the pathogenesis of marrow fibrosis frequently associated with myeloproliferative disorders. Two growth factors, platelet derived growth factor (PDGF) and epidermal growth factor (EGF), cooperatively stimulated the growth of passaged fibroblasts as well as fibroblast colony-forming cells. Transforming growth factor-beta augmented the growth of fibroblasts at low concentrations in the presence of EGF and/or PDGF, but inhibited that of colony-forming cells in the presence of PDGF or EGF. These results suggest that the growth of fibroblasts causing marrow fibrosis might be finely regulated, depending on the concentrations of growth factors released or leaked from platelets or megakaryocytes into marrow environment.