Ultrastructural study shows morphologic features of apoptosis and para-apoptosis in megakaryocytes from patients with idiopathic thrombocytopenic purpura

To investigate whether altered megakaryocyte morphology contributes to reduced platelet production in idiopathic thrombocytopenic purpura (ITP), ultrastructural analysis of megakaryocytes was performed in 11 ITP patients. Ultrastructural abnormalities compatible with (para-)apoptosis were present in 78% +/- 14% of ITP megakaryocytes, which could be reversed by in vivo treatment with prednisone and intravenous immunoglobulin. Immunohistochemistry of bone marrow biopsies of ITP patients with extensive apoptosis showed an increased number of megakaryocytes with activated caspase-3 compared with normal (28% +/- 4% versus 0%). No difference, however, was observed in the number of bone marrow megakaryocyte colony-forming units (ITP, 118 +/- 93/105 bone marrow cells; versus controls, 128 +/- 101/105 bone marrow cells; P =.7). To demonstrate that circulating antibodies might affect megakaryocytes, suspension cultures of CD34+ cells were performed with ITP or normal plasma. Morphology compatible with (para-)apoptosis could be induced in cultured megakaryocytes with ITP plasma (2 of 10 samples positive for antiplatelet autoantibodies). Finally, the plasma glycocalicin index, a parameter of platelet and megakaryocyte destruction, was increased in ITP (57 +/- 70 versus 0.7 +/- 0.2; P =.009) and correlated with the proportion of megakaryocytes showing (para-) apoptotic ultrastructure (P =.02; r = 0.7). In conclusion, most ITP megakaryocytes show ultrastructural features of (para-) apoptosis, probably due to action of factors present in ITP plasma.     

Investigation of megakaryocyte apoptosis in children with acute and chronic idiopathic thrombocytopenic purpura

OBJECTIVE: Although the platelet destruction shows a primary role in the thrombocytopenia of idiopathic thrombocytopenic purpura (ITP), it has been demonstrated that impaired platelet production may also contribute to the severity of thrombocytopenia in ITP. The present study examined megakaryocyte apoptosis in bone marrow aspirates of children with acute and chronic ITP and investigated the role of megakaryocyte apoptosis in ITP pathophysiology. METHODS: Thirteen children diagnosed with acute ITP and eight children diagnosed with chronic ITP comprised the study group. Ten children, who were hospitalized for scoliosis operation but healthy otherwise, comprised the control group. In all children, megakaryocytes were isolated from the same amount of bone marrow aspirate samples using MACS CD61 MicroBeads (Miltenyl Biotec, Auburn, CA, USA). Megakaryocyte apoptosis was studied with transferase-mediated d-UTP-bitin nick end-labeling method. RESULTS: Isolated megakaryocyte counts did not differ significantly between acute ITP, chronic ITP and control groups. The percentage of apoptotic megakaryocytes did not differ significantly between acute ITP group and control group and between chronic ITP group and control group. The percentage of apoptotic megakaryocytes in patients with chronic ITP was significantly lower than the patients with acute ITP. There was no correlation between the percentage of apoptotic megakaryocytes and platelet counts of the cases. CONCLUSIONS: Increased megakaryocytic apoptosis does not play a role in the pathogenesis of dysmegakaryopoiesis and impaired platelet production in children with ITP. Decreased megakaryocyte apoptosis in cases with chronic ITP may be due to suppression of megakaryocyte maturation, as the terminal phase of the megakaryocyte lifespan is characterized by the onset of apoptosis.     

The relation of thrombokinetics to bone marrow megakaryocytes in idiopathic thrombocytopenic purpura (ITP).

In 23 patients with untreated idiopathic thrombocytopenic purpura (TP), the relation of thrombokinetics to quantitative determinations of megakaryocytes in bone marrow sections was studied. The megakaryocytes were classified into maturation stages, and platelet sizes were determined. Megarkaryocyte number and volume per microliter of bone marrow were significantly higher in ITP as compared to controls. The megakaryocyte number and volume were inversely related to the peripheral platelet count. Platelet production rate was significantly increased in ITP and related to the megakaryocyte number and volume. The megakaryocytes were shifted towards more immature forms in ITP, suggesting an increased turnover rate of the expanded recognizable metakaryocyte compartment. Platelet size was significantly increased in ITP, and the mean platelet diameter was 1.6 times normal. There was a significant relationship between platelet size and platelet production rate, as well as an inverse relationship between platelet size and platelet mean life-span (MLS). There was also a significant correlation between platelet size and the proportion of young megakaryocytes.     

Megakaryocyte Quantifications in Relation to Thrombokinetics in Primary Thrombocythaemia and Allied Diseases

Megakaryocyte morphology was studied quantitatively in primary thrombocythaemia (PT) and in chronic myelogenous leukaemia (CML). The relation of thrombokinetics to megakaryocyte quantifications was evaluated in PT and compared to previously obtained results in polycythaemia Vera (PV) and idiopathic thrombocytopenic purpura (ITP). Megakaryocyte area, number and volume per μl bone marrow were significantly higher in PT as compared to controls. The nuclear lobe number was significantly increased and the megakaryocytes were shifted towards more mature forms, suggesting a prolonged megakaryocyte generation time. In CML the megakaryocyte number and volume per μl bone marrow were also significantly above normal, but the megakaryocyte area, number of lobes and degree of megakaryocytic maturation were significantly below normal. Platelet production was in PT 6.2 times normal and proportional to the increase in megakaryocyte volume which was 6.8 times normal. In PV with major splenomegaly the mean platelet production rate was higher (9.5 times normal) although their peripheral platelet count was lower than in PT. This discrepancy is explained by the greatly enlarged splenic platelet pool in the PV patients. In ITP the mean platelet production rate was 2.2 to 3 times normal and was significantly lower than in PT and PV.     

CD8+ T cells suppress autologous megakaryocyte apoptosis in idiopathic thrombocytopenic purpura

To investigate the effect and mechanism of the CD8⁺ T cells in bone marrow on autologous megakaryocytopoiesis in idiopathic thrombocytopenic purpura (ITP) patients, we prepared bone marrow mononuclear cells (MNCs) from 15 chronic ITP patients and 13 controls. MNCs were cultured in vitro directly (MNC group) or after depleting CD8⁺ T cells (CD8⁺ T-dep group) or adding purified autologous CD8⁺ T cells to CD8⁺ T-dep MNCs (Coculture group) or adding dexamethasone to the coculture (DEX group) all in semi-solid and liquid culture systems. The quantity and quality of megakaryocytes were measured. The megakaryocyte count was increased in the presence of autologous CD8⁺ T cells of patients with chronic ITP, while platelet production was reduced. In addition, lower percentages of polyploidy and apoptotic megakaryocytes, and higher levels of soluble Fas (sFas) in supernatant were observed. Dexamethasone successfully corrected this effect of CD8⁺ T cells on autologous megakaryocytopoiesis. These studies provide evidence that activated CD8⁺ T cells in bone marrow of patients with chronic ITP might suppress megakaryocyte apoptosis, leading to impaired platelet production. Megakaryocyte apoptosis would be a novel target for the management of ITP.     

Plasma thrombopoietin levels in thrombocytopenic states: implication for a regulatory role of bone marrow megakaryocytes

To evaluate the diagnostic value of thrombopoietin (TPO, c-mpl ligand) measurements, and clarify the regulatory mechanisms of TPO in normal and in thrombocytopenic conditions, the plasma TPO concentration was determined in normal individuals (n = 20), umbilical cord blood (n = 40), chronic idiopathic thrombocytopenic purpura (ITP; n = 16), in severe aplastic anaemia (SAA; n = 3), chemotherapy-induced bone marrow hypoplasia (n = 10), myelodysplastic syndrome (MDS; n = 11), and sequentially during peripheral blood progenitor cell transplantation (n = 7). A commercially available ELISA and EDTA-plasma samples were used for the analysis. The plasma TPO concentration in the normals and umbilical cord blood were 52 ± 12 pg/ml and 66 ± 12 pg/ml, respectively. The corresponding values in patients with SAA and chemotherapy-induced bone marrow hypoplasia were 1514 ± 336 pg/ml and 1950 ± 1684 pg/ml, respectively, and the TPO concentration, measured sequentially after myeloablative chemotherapy and peripheral blood progenitor cell transplantation, was inversely related to the platelet count. In contrast, the plasma TPO recorded in patients with ITP (64 ± 20 pg/ml) and MDS (68 ± 23 pg/ml) were only slightly higher than normal levels. In conclusion, TPO levels were significantly elevated in patients in which bone marrow megakaryocytes and platelets in circulation were markedly reduced, whereas TPO levels were normal in ITP patients, and only slightly increased in the MDS patients. These latter patients displayed a preserved number of megakaryocytes in bone marrow biopsies. Our data support the suggestion that megakaryocyte mass affects the plasma TPO concentration. In thrombocytopenic patients a substantially increased plasma TPO implies deficient megakaryocyte numbers. However, TPO measurements do not distinguish between ITP and thrombocytopenia due to dysmegakaryopoiesis, as seen in MDS patients.     

Different patterns of platelet turnover in chronic idiopathic thrombocytopenic purpura

Platelet turnover, platelet production, platelet mean life span (MLS), platelet count, mean platelet volume (MPV) and platelet-associated antibodies have been examined in 26 patients with chronic idiopathic thrombocytopenic purpura (ITP) and in 1 patient with hypomegakaryocytic thrombocytopenia (HT). 15 ITP patients had normal or increased platelet turnover and platelet production, while 11 had subnormal values despite shortened MLS, while the patient with HT had normal MLS. The differences between the two groups with high and low platelet turnover were statistically significant. No correlation was found between kinetics parameters and bone marrow pattern in a total of 19 patients examined. These data suggest that in some cases of chronic ITP, the pathogenesis of thrombocytopenia can be due not only to the peripheral destruction of platelets, but also to a deficient platelet production by megakaryocytes. Since the number of megakaryocytes in bone marrow slides is not decreased in the low turnover compared with the high turnover group, it is possible that an impaired pattern of megakaryocyte maturation be the cause of the low platelet production in these patients, unlike in the HT patient where megakaryocytes are almost absent.     

On the analysis of platelet survival curves and the calculation of platelet production and destruction

Platelet survival, platelet production and megakaryocyte quantifications were studied in control subjects and in patients with idiopathic thrombocytopenic purpura (ITP) and primary thrombocythaemia (PT). A platelet death probability function (DPF), which gives the expected probability of a randomly chosen platelet to be destroyed within the nextcoming short time interval, was constructed on the basis of the present knowledge of platelet function and the factors that influence its survival. Starting from this function platelet age and life span distributions and the function for the survival curve were derived. Platelet mean life span (MLS) was in controls 6.9d, in PT 5.2Dd and in ITP 0.44d. Determinations of platelet life span and platelet age distributions revealed a considerable variation in platelet life spans about these means and a great difference in platelet age compositions between the 3 groups of subjects studied. The function for the platelet survival curve, derived from the DPF, was employed in the calculation of platelet production and there was a highly significant relationship between platelet production and megakaryocyte volume per microliter bone marrow giving mutual confirmation to the 2 determinations and to the correctness of the death probability function.     

Indirect study of thrombopoiesis (TPO, reticulated platelets, glycocalicin) in patients with hereditary macrothrombocytopenia

Chronic isolated hereditary macrothrombocytopenia (CHMT) is a congenital form of macrothrombocytopenia that seems to be due to defective production secondary to a disturbance in megakaryocyte fragmentation. To better understand the pathogenesis of thrombopoiesis in this hereditary thrombocytopenic disorder, we determined the percentage of reticulated platelets (RP), plasma glycocalicin (GC) and thrombopoietin (TPO) levels in 29 patients with CHMT, 23 patients with immune thrombocytopenic purpura (ITP), and 17 patients with thrombocytopenia secondary to decreased bone marrow megakaryocytes (hypoplasia). The % RP was similar in CHMT (2.27 +/- 1.33) and hypoplasia (1.98 +/- 1.35) patients and markedly lower than that in ITP patients (8.80 +/- 7.97; p <0.001), suggesting that the production of new platelets is reduced in CHMT. Plasma GC was within the normal range (0.84 +/- 0.16 microg/mL) both in patients with CHMT (0.63 +/- 0.20 microg/mL) and ITP (0.82 +/- 0.90 microg/mL), while it was significantly decreased in patients with hypoplasia (0.16 +/- 0.04 microg/mL; p < 0.001). When the GC value was normalized for platelet count, the GC index was normal in CHMT patients (2.05 +/- 1.1) and in patients with hypoplasia (0.85 +/- 0.10) while it was significantly increased in ITP patients (10.88 +/- 18.00; p<0.001); thus, patients with CHMT seem to have a normal platelet turnover. TPO was significantly increased in CHMT (195 +/- 72 pg/ml) as compared with normal (80 +/- 53 pg/ml; p < 0.002); however, the mean level was not as high as in ITP patients (345 +/- 167 pg/mL; p < 0.001). This finding suggests that CHMT syndrome is not secondary to a defective production of TPO and that megakaryocyte mass is nearly normal.     

Megakaryocyte c-Mpl expression in chronic myeloproliferative disorders and the myelodysplastic syndrome: immunoperoxidase staining patterns and clinical correlates

The objectives of this study were to expand on recent observations that have suggested decreased thrombopoietin receptor (c-Mpl) expression in megakaryocytes of patients with polycythemia vera (PV) and agnogenic myeloid metaplasia (AMM). We applied an immunoperoxidase method with anti-c-Mpl antibody to 55 bone marrow sections from previously untreated patients with chronic myeloproliferative disorder (CMPD) or myelodysplastic syndrome (MDS). These included 8 patients with PV, 15 with AMM, 9 with essential thrombocythemia, 5 with chronic myelocytic leukemia, 9 with the 5q-syndrome and 9 with MDS with fibrosis. The findings were compared with those in four patients with reactive erythrocytosis (RE), six with immune thrombocytopenic purpura (ITP) and five normal controls. Staining intensity (SI) was moderate to strong both in normal controls and in patients with RE or ITP. In contrast, SI was weak in variable proportions of the megakaryocytes in every one of the aforementioned clonal myeloid disorders. The staining pattern (SP) was relatively uniform in MDS and heterogeneous in CMPD. Neither SI nor SP was significantly correlated with certain clinical or laboratory parameters. We concluded that altered megakaryocyte c-Mpl expression may be a nonspecific phenomenon in various subtypes of both CMPD and MDS. However, the characteristic staining patterns may complement the morphological distinction between clonal and reactive myeloproliferation.     

Suppression of in vitro megakaryocyte production by antiplatelet autoantibodies from adult patients with chronic ITP

Chronic immune thrombocytopenic purpura (ITP) is manifested by autoantibody-induced platelet destruction. Platelet turnover studies suggest that autoantibody may also affect platelet production. To evaluate this, we studied the effect of plasma from adult patients with chronic ITP on in vitro megakaryocyte production. CD34(+) cells, obtained from healthy donors, were cultured in medium containing PEG-rHuMGDF and 10% plasma from either ITP patients or healthy subjects. Cultures containing plasma from 12 of 18 ITP patients showed a significant decrease (26%-95%) in megakaryocyte production when compared with control cultures. Positive ITP plasmas not only reduced the total number of megakaryocytes produced during the culture period but also inhibited megakaryocyte maturation, resulting in fewer 4N, 8N, and 16N cells. The role of antibody in this suppression is supported by 2 factors: (1) immunoglobulin G (IgG) from ITP patients inhibited megakaryocyte production when compared with control IgG; and (2) adsorption of autoantibody, using immobilized antigen, resulted in significantly less inhibition of megakaryocyte production when compared with unadsorbed plasma. These results show that plasma autoantibody from some adult patients with ITP inhibits in vitro megakaryocyte production, suggesting that a similar effect may occur in vivo.     

Kinetics of megakaryocyte progenitor cells in idiopathic thrombocytopenic purpura

Summary The number and proliferative state of megakaryocyte progenitor cells (CFU-Meg) were compared between 13 patients with idiopathic thrombocytopenic purpura (ITP) and hematologically normal controls. The mean frequency of CFU-Meg assayed by the plasma clot method was 27.8 ± 12.2 (± SD)/2×10⁵ bone marrow light-density cells for the ITP patients, which did not differ significantly from the control value of 31.9 ± 16.1. The percentage of CFU-Meg in DNA synthesis estimated by the³H-thymidine suicide technique was 41.3% ± 9.2% in ITP, which was significantly greater than the control value of 27.1% ± 7.4% (P < 0.01). The megakaryocyte counts for histological sections prepared from bone marrow aspirates from the ITP patients and controls were 34.5 ± 8.5/mm² and 11.2 ± 5.8/mm², respectively, with the difference being highly significant (P < 0.001). These results suggest that increased cycling activity in a quantitatively unchanged CFU-Meg pool may lead to increased megakaryocytes in the bone marrow of ITP patients.     

The Relation of Platelet Kinetics to Bone Marrow Megakaryocytes in Chronic Granulocytic Leukaemia

The relation of thrombokinetics to quantitative determinations of megakaryocytes (mgkc) in bone marrow sections was studied in 11 consecutive cases of untreated Ph¹-positive chronic granulocytic leukaemia (CGL). The results were compared with controls and with previously obtained data in polycythaemia vera (PV), primary thrombocythaemia (PT) and in idiopathic thrombocytopenic purpura (ITP). Platelet survival was significantly reduced in CGL. Platelet production was 5.8 x normal and the mgkc number and volume/μl bone marrow were significantly increased as compared to controls. The increase in mgkc volume was not in proportion to that of number due to a significant decrease of mgkc size. Platelet production was strongly related to mgkc number/mm² and to the mgkc volume/μl bone marrow. The platelet production rate in relation to a unit of mgkc volume/μl bone marrow was, however, greater in CGL than in controls, PV, PT and ITP. The chief reason for this is most probably the greater expansion of the total bone marrow mass in CGL.     

Interleukin-7 is decreased and maybe plays a pro-inflammatory function in primary immune thrombocytopenia

Primary immune thrombocytopenia (ITP) is an autoimmune disease with many immune dysfunctions, including over-proliferation and apoptosis resistance of auto-reactive lymphocytes. This study aimed to determine the effects of interleukin (IL)-7 on the cytokine production and survival of peripheral blood mononuclear cells and bone marrow mononuclear cells from ITP patients. We found that the plasma IL-7 levels in peripheral blood from ITP patients were lower than that of the normal controls, and it had positive correlation with platelet counts. However, the levels of IL-7 did not change in bone marrow serum of ITP patients compared with that of normal controls. The result of further stimulation experiments in vitro showed that IL-7 up-regulated the apoptosis of autologous platelets, promoted the proliferation and secretion of interferon-γ, tumor necrosis factor-α as well as IL-10 of lymphocyte both from peripheral blood and bone marrow. As the role of IL-7 in apoptosis-resistance and stimulation of pro-inflammatory cytokines, we speculated that decreased IL-7 in peripheral blood, maybe, is a consequence of the negative feedback of the pro-inflammatory function in ITP patients.     

Impaired survival of bone marrow GPIIb/IIIa+ megakaryocytic cells as an additional pathogenetic mechanism of HIV-1-related thrombocytopenia

Glycoproteic (GP) IIb/IIIa⁺ megakaryocytic cells were purified from the bone marrow (BM) of 15 HIV-1 seropositive thrombocytopenic patients, eight HIV-1 seronegative patients affected by immune thrombocytopenic purpura (ITP) and 14 HIV-1 seronegative normal donors. The presence of apoptosis was evaluated in freshly isolated GPIIb/IIIa⁺ cells by flow cytometry after propidium iodide staining and electron microscopy. GPIIb/IIIa⁺ cells from HIV-1 seropositive thrombocytopenic patients showed a significant (  P  < 0.001) increase of apoptosis with respect to both HIV-1 seronegative ITP patients and normal donors. Moreover, the degree of apoptosis in bone marrow GPIIb/IIIa⁺ cells purified from HIV-1 seropositive thrombocytopenic patients was inversely (  P  < 0.01) related to the count of circulating platelets, whereas it did not show any significant correlation with the absolute number of circulating CD4 T cells, the CD4/CD8 ratio or the presence of proviral gag DNA sequences. Therefore neither an advanced stage of HIV-1 disease nor a direct infection with HIV-1 seems to play a primary role in the impaired survival of BM GPIIb/IIIa⁺ megakaryocytic cells. These findings strengthen the notion that, besides the immune targeting of peripheral platelets, an impairment of the bone marrow megakaryocyte compartment may also contribute to the pathogenesis of HIV-1 related thrombocytopenia.     

网织血小板测定对血小板减少疾病诊断价值的探讨

目的　探讨外周血网织血小板 (RP)数值的变化对各型血小板减少疾病的诊断价值 ;外周血RP与骨髓中巨核细胞 (MK)增生程度的关系。方法　以噻唑橙作为RNA的荧光染料 ,利用流式细胞仪测定外周血中含有RNA的RP ,并计算RP(% )及RP绝对值。结果　 (1)正常对照组 :RP(8 4±2 5 ) % ,RP绝对值为 (16 8± 6 8)× 10 9/L。 (2 )原发性血小板减少性紫癜 (ITP)和脾功能亢进症患者RP(% )显著高于正常对照组 ,而RP绝对值显著低于正常对照组 (P <0 0 1) ,在不同MK增生级别的ITP患者中 ,RP(% )、RP绝对值在各组之间均无差异 ;再生障碍性贫血患者RP(% )及绝对值均低于正常对照组 (P <0 0 5 ,P <0 0 1) ;而急性白血病、骨髓增生异常综合征患者RP(% )与正常对照组无明显差异 (P >0 0 5 ) ,但其RP绝对值明显低于正常对照组 (P <0 0 1)。 (3)上述疾病患者 ,经治疗有效者RP(% )恢复正常 ,而无效或疗效欠佳者 ,则RP(% )几无变化。结论　外周血RP测定 ,有助于血小板减少疾病的病因学诊断 ,是血小板减少疾病一有价值的诊断依据 ,也是疗效判断的监控指标。外周血RP与骨髓中MK增生的程度无相关性     

Immune thrombocytopenic purpura (ITP) plasma and purified ITP monoclonal autoantibodies inhibit megakaryocytopoiesis in vitro

To determine if megakaryocytes are targeted by immune thrombocytopenic purpura (ITP) autoantibodies, as are platelets, we have studied the effects of ITP plasma on in vitro megakaryocytopoiesis. Umbilical cord blood mononuclear cells were incubated in the presence of thrombopoietin and 10% plasma from either ITP patients (n = 53) or healthy donors. The yield of megakaryocytic cells, as determined by flow cytometry, was significantly reduced in the presence of ITP plasma containing antiplatelet glycoprotein Ib (GPIb) autoantibodies (P <.001) as compared with both the control and patient plasma with no detectable anti-GPIIb/IIIa or anti-GPIb autoantibodies. Platelet absorption of anti-GPIb autoantibodies in ITP plasmas resulted in double the megakaryocyte production of the same plasmas without absorption, whereas platelet absorption of control plasma had no effect on megakaryocyte yield. Furthermore, 2 human monoclonal autoantibodies isolated from ITP patients, 2E7, specific for human platelet glycoprotein IIb heavy chain, and 5E5, specific for a neoantigen on glycoprotein IIIa expressed on activated platelets, had significant inhibitory effects on in vitro megakaryocytopoiesis (P <.001). Taken together, these data indicate that autoantibodies against either platelet GPIb or platelet GPIIb/IIIa in ITP plasma not only are involved in platelet destruction, but may also contribute to the inhibition of platelet production.     

Evaluation of platelet kinetics in patients with liver cirrhosis: similarity to idiopathic thrombocytopenic purpura

BACKGROUND: Thrombocytopenia is a common manifestation of liver cirrhosis (LC), but its underlying mechanism is not fully understood. The purpose of the present paper was to evaluate the platelet kinetics in LC patients by examining several non-invasive convenient markers. METHODS: Fifty-seven LC patients, 32 patients with idiopathic thrombocytopenic purpura (ITP), 12 with aplastic anemia (AA), and 29 healthy individuals were studied. Plasma thrombopoietin was measured by enzyme-linked immunosorbent assay. Absolute reticulated platelet (RP) count and plasma glycocalicin were used as indices for thrombopoiesis, and the indices for platelet turnover were the RP proportion and the plasma glycocalicin normalized to the individual platelet count (GCI). RESULTS: There was no difference in thrombopoietin levels between LC patients and healthy controls. The RP proportion and GCI were significantly higher and the absolute RP count and glycocalicin significantly lower in LC patients than in healthy controls. These markers in ITP and LC patients were comparable, but significantly different from those in AA patients. The bone marrow megakaryocyte density in LC and ITP patients was similar, and significantly higher than in AA patients. CONCLUSIONS: Cirrhotic thrombocytopenia is a multifactorial condition involving accelerated platelet turnover and moderately impaired thrombopoiesis. Thrombopoietin deficiency is unlikely to be the primary contributor to cirrhotic thrombocytopenia.     

Platelet Survival and Platelet Production in Idiopathic Thrombocytopenic Purpura (ITP)

S ummary . Platelet mean life span (MLS) and platelet production were measured in 3–5 patients with idiopathic thrombocytopenic purpura (ITP) and in 21 healthy subjects.
The mean platelet production in ITP was 2.3 times normal: the highest values were 3–5 times normal. There was a highly significant negative correlation between platelet production and peripheral platelet count. With platelet counts above 50000μl, platelet turnover was within the upper part of the normal range, but with lower platelet counts, turnover progressively increased. It is concluded that the bone marrow in ITP increases platelet production in response to a low platelet count and that this response does not differ from that hitherto known to occur in man and animals rendered thrombocytopenic by thrombopheresis.
The disappearance curve of ⁵¹Cr labelled platelets in ITP consists of two components, a rapid initial one covering the first 15 min after infusion and then a slower one. The pattern was the same whether autologous or homologous platelets were used for labelling. It is suggested that the initial part of the curve does not represent in vivo survival but is due to slight damage to the platelets during the labelling procedure. These slightly damaged cells can resume normal viability when infused into a normal recipient but are rendered less viable when further damaged by platelet antibodies in patients with ITP. This explains the low recovery of infused labelled platelets in ITP recipients, despite the fact that the size of their splenic platelet pool is normal.     

The relation of megakaryocyte ploidy to platelet volume

To determine how alterations of megakaryocyte proliferation will affect platelet production, we measured mean platelet volume (MPV), platelet volume heterogeneity, platelet count, and mean megakaryocyte ploidy in 42 patients. In normal subjects, mean platelet volume and megakaryocyte ploidy were related inversely but nonlin-early to platelet count, whereas mean platelet volume and platelet volume heterogeneity were related directly. In patients with immune thrombocytopenic purpura (low platelet count, MPV above normal, and increased megakaryocyte ploidy), and in those with reactive thrombocytosis (high platelet count, low MPV and megakaryocyte ploidy), the relation of MPV to megakaryocyte ploidy, platelet volume heterogeneity, and platelet count resembled or extended the relations found in normal subjects. By contrast, in patients with aplastic anemia or megaloblastic anemia, or in patients who were undergoing chemotherapy for leukemia, heterogeneity was increased abnormally at any MPV, and both MPV and megakaryocyte ploidy were substantially lower, at any platelet volume, than in normals or the above other groups. The most common ploidy class was 8N in all patients, and the mean megakaryocyte ploidy correlated directly and linearly with mean platelet volume. The data show that bone marrow with megakaryocytes of higher ploidy produces platelets that are both larger and more heterogeneous.