Circulating thrombopoietin in systemic sclerosis.

OBJECTIVE: To investigate circulating thrombopoietin (TPO) concentrations in systemic sclerosis (SSc). METHODS: TPO concentrations were measured by ELISA in serum samples of 13 patients (11 female, 2 male) with diffuse SSc, 15 healthy controls (13 female, 2 male), and 15 patients (13 female, 2 male) with rheumatoid arthritis (RA). Thrombocyte counts of patients with SSc and RA and controls were recorded. RESULTS: Median TPO concentrations were 115 (164) in SSc, 76 (32) in RA, and 62 (34) pg/ml in controls. Median serum TPO concentration in the SSc group was significantly higher than other groups; there was no difference between controls and patients with RA (p<0.001 for both comparisons). Median platelet counts of SSc, RA, and controls were 224+/-58x10(9)/l, 238+/-44x10(9)/l, and 272+/-35x10(9)/l, respectively. There was no correlation between thrombocyte counts and TPO levels in any group. CONCLUSION: We show that patients with SSc have higher serum TPO concentrations compared to healthy controls and patients with RA. It can be hypothesized that TPO mediated release of particular growth factors may participate in the pathogenesis of the fibrotic process of SSc.     

Early elevation of serum thrombopoietin levels and subsequent thrombocytosis in healthy preterm infants

To verify pathophysiological mechanisms underlying thrombocytosis in low-birth-weight (LBW) preterm babies, we evaluated kinetic changes in platelet counts and thrombopoietic cytokines including thrombopoietin (TPO), interleukin 6 (IL-6) and IL-11 in 24 uncomplicated preterm infants. Platelet counts in cord blood (CB) (265 +/- 64 x 10(9)/l) were similar to adult levels, increased by d 14 (473 +/- 140 x 10(9)/l), and then remained fairly constant. Thrombocytosis (> 500 x 10(9)/l) was observed in 9/24 (38%) subjects. Mean TPO level in CB was 5.11 +/- 1.51 fmol/ml, peaked at d 2 (7.64 +/- 3.28 fmol/ml), decreased at d 5 (3.93 +/- 1.67 fmol/ml), and thereafter kept fairly constant during the remaining neonatal period. Compared with term infants, mean TPO levels of preterm infants in CB and at d 2 were significantly higher (P < 0.01). There was an inverse correlation between platelet counts and TPO levels (r = 0.45, P < 0.001, n = 88). Preterm neonates with thrombocytosis had significantly higher TPO values in CB than those without thrombocytosis (P < 0.05). There was no significant relationship between platelet counts and IL-6. IL-11 was not detectable. These results suggest that an early elevation of serum TPO levels is related to the subsequent thrombocytosis in LBW preterm infants.     

Elevation of serum thrombopoietin precedes thrombocytosis in acute infections

To clarify the mechanisms underlying thrombocytosis secondary to infections, we longitudinally studied serum levels of thrombopoietin (TPO) and interleukin (IL)-6 in 15 infants and young children with prominent thrombocytosis (platelets >700 x 10(9)/l) following acute infections and 116 age-matched controls using an enzyme-linked immunosorbent assay. The subjects included nine patients with bacterial infections, three with viral infections and three with non-determined pathogens. TPO values in the controls were 2.24 +/- 0.87 fmol/ml (mean +/- SD) with a 95% reference interval of 0.85-4.47 fmol/ml. In the first week of infection, platelet counts were normal, but TPO values increased (approximately 10.73 fmol/ml). TPO levels peaked on day 4 +/- 2 at 6.44 +/- 2.37 fmol/ml and then fell gradually. When platelet counts peaked in the second and third weeks, TPO levels were similar to the controls. IL-6 levels in the first week rose and dropped more rapidly than TPO. Serum TPO values were significantly correlated with C-reactive protein levels (r = 0.688, P < 0.001) and IL-6 levels (r = 0.481, P = 0.027). These results suggest that TPO contributes to thrombocytosis following infections in conjunction with IL-6, arguing for additional regulatory mechanisms of blood TPO levels.     

Elevated serum interleukin-6 levels in patients with reactive thrombocytosis

Interleukin-6 (IL-6) is known to promote megakaryocytopoiesis in vitro and raise platelet counts in vivo. To determine if there is a relationship between circulating IL-6 and thrombocytosis in man, we measured bioactive IL-6 in the serum of 13 patients with myeloproliferative disorders and 143 patients with reactive thrombocytosis having platelet counts greater than or equal to 600 x 10(9)/l. IL-6 activity was assayed using the IL-6-responsive B9 cell line. Seventy-one controls with normal platelet counts had a mean IL-6 level of 2.19 U/ml +/- 1.08 (SD). None of the 13 patients with myeloproliferative disorders had elevated IL-6 levels (1.56 U/ml +/- 1.2). In contrast, serum IL-6 levels of 143 patients (158 samples) with reactive thrombocytosis were significantly greater than controls (38.3 U/ml +/- 94.6; P less than 0.001), with 83% of the samples showing elevated serum IL-6. No significant correlation was observed between serum IL-6 levels and platelet counts in the reactive thrombocytosis group. We conclude that elevated IL-6 is associated with reactive thrombocytosis, and hypothesize that the increased platelet count in many cases is causally related to elevated IL-6.     

Serum thrombopoietin levels in patients with reactive thrombocytosis due to lung cancer and in patients with essential thrombocythemia

In patients with thrombocytosis normal to increased serum thrombopoietin (TPO) levels have been reported. The aim of this study was to investigate the relationship between serum TPO concentration, platelet number and plasma levels of fibrinogen in patients with reactive thrombocytosis (RT) due to lung cancer and in patients with essential (primary) thrombocythemia (ET). A total of 70 newly diagnosed patients with RT or ET (platelet counts >600 G/l) were studied: 45 with RT due to lung cancer (25 with non-small cell lung cancer, NSCLC and 20 with small cell lung cancer, SCLC), and 25 with ET. Twenty normal volunteers were used as controls. TPO was measured by immunoassay technique (ELISA). Mean serum TPO values in patients with RT due to lung cancer were statistically significantly higher than those in patients with ET or in controls. The highest platelet count was seen in patients with ET, and mean plasma fibrinogen levels were the highest in RT patients. In NSCLC patients mean serum TPO concentrations were higher (not statistically significant) than in SCLC, and a statistically significant relationship between TPO serum concentration and fibrinogen level was observed. No correlations between platelet counts and TPO serum concentrations were found. Our results indicate increased serum TPO levels in patients with thrombocytosis in lung cancer which may be related to the activity of neoplasms. In addition, it is postulated that the relatively low TPO values in patients with ET may result from a dysregulation of the feedback loop involved in platelet production.     

Impaired liver function and retroviral activity are risk factors contributing to HIV-associated thrombocytopenia. Swiss HIV Cohort Study.

OBJECTIVE: To investigate the relationship between thrombopoetin (TPO) serum levels and HIV-associated thrombocytopenia. DESIGN AND METHODS: The relationship between TPO levels and severity of HIV-associated thrombocytopenia was investigated. Thirty-eight patients (19 patients with 30-96x10(9) platelets/l and 19 patients with <10x10(9) platelets/l) were matched with 38 HIV-positive non-thrombocytopenic patients (>150x10(9) platelets/l). RESULTS: HIV-positive patients with normal platelet counts had a median TPO serum level of 137 pg/ml. Patients with 30-96x10(9) platelets/l had decreased TPO levels with a median of 90 pg/ml (P = 0.016), and were more likely to have elevated serum aspartate-transferase levels (P<0.001) and hepatomegaly by palpation or ultrasound imaging (P = 0.005). The median TPO serum level of HIV-infected patients with severe thrombocytopenia was 110 pg/ml (non-significant). All patients with severe thrombocytopenia were positive for antibodies against hepatitis B virus core antigen, compared with 80% of HIV-infected persons without thrombocytopenia. Patients with severe thrombocytopenia were more likely to have high HIV replication compared to patients with normal platelet counts (P = 0.02), and reduction of plasma HIV-1 RNA levels was associated with increasing platelet counts. Severe thrombocytopenia was not associated with liver disease. CONCLUSIONS: Liver disease predisposes for low TPO serum levels and mild thrombocytopenia. High retroviral activity predisposes for severe, immune thrombocytopenic purpura-like thrombocytopenia. At least two distinct categories of severe HIV-associated thrombocytopenia exist, one responsive to antiretroviral treatment and one non-responsive to antiretroviral treatment.     

Thrombopoietin serum concentration in patients with reactive and myeloproliferative thrombocytosis

 We wished to test whether thrombopoietin (TPO) is entirely regulated by receptor binding or if other factors may play a role in the mechanism of TPO regulation. Therefore, we analyzed the TPO serum levels in 43 patients with reactive (secondary) thrombocytosis and in 37 with myeloproliferative thrombocytosis. Thrombocytosis was defined as a platelet level greater than 440×10⁹/l. Forty-two patients (98%) with reactive thrombocytosis had high concentrations of IL-6 correlating with elevated C-reactive protein levels. Twenty-three patients (53%) in this group had TPO serum concentrations of more than 300 pg/ml (normal: below 300 pg/ml). Only nine patients (24%) with myeloproliferative thrombocytosis had TPO serum levels above normal range, whereas 28 patients (76%) had normal levels of TPO. No correlation between the TPO serum levels and the concentrations of IL-6 or EPO was established. The other investigated thrombopoietic cytokines (IL-3, IL-11, GM-CSF) were unmeasurable; therefore, a correlation could not be assessed. We conclude that TPO concentrations are not strictly inversely related to platelet count. TPO serum levels are elevated especially in a considerable percentage of patients with reactive thrombocytosis, arguing for the existence of additional mechanisms of TPO regulation. Received: February 28, 1998 / Accepted: August 18, 1998     

Transient thrombopoietin peak after liver transplantation for end-stage liver disease

Knowledge about synthesis of thrombopoietin (TPO) by human liver cells is now well established and makes the study of TPO serum levels and interdependency with platelet concentrations important before and after liver transplantation. We followed these variables in 14 patients suffering from primary biliary cirrhosis (group A), 10 with hepatitis B (group B) and nine with hepatitis C (group C) infections, as well as 11 patients suffering from alcoholic cirrhosis (group D). In the pretransplant serum samples, TPO levels and platelet counts revealed median values (range) of 112.75 pg/ml (5.0-349.3) in group A, 67.8 pg/ml (14.8-249.9) in B, 68.6 pg/ml (31.4-147.3) in C and 57.9 pg/ml (25.2-264.2) in D for TPO, and 138 x 10(9)/l (36-243) in A, 48 x 10(9)/l (22-129) in B, 105 x 10(9)/l (32-176) in C and 109 x 10(9)/l (33-285) in D for platelets, the latter levels being abnormally reduced. Within 2-3 d of transplantation, the TPO levels started to increase to transient peaks of mostly 5-10 times baseline, which were followed by continuous correction of thrombocytopenia. Splenomegaly was identified to be an important co-factor of thrombocytopenia in groups A and D. We conclude that decreased TPO production in patients with end-stage liver diseases is reverted by orthotopic liver transplantation.     

Chronic thrombocytopenia of childhood: use of non-invasive methods in clinical evaluation

OBJECTIVES: An unselected group of 21 children with chronic thrombocytopenia was investigated to understand the patients' platelet abnormality better. METHODS: Platelet counts, mean platelet volumes (MPV), membrane glycoproteins and Fcgamma receptor type IIA (FcgammaRIIA) polymorphism H131R, reticulated platelets (% RP), antiplatelet antibodies and plasma thrombopoietin (TPO) were measured. RESULTS: Sixteen patients had idiopathic thrombocytopenic purpura (ITP) (group 1: platelets < 50 x 10(9)/L, n = 6; group 2: 50-99 x 10(9)/L, n = 4; group 3: 100-149 x 10(9)/L, n = 4; group 4: splenectomised patients with normal platelet counts, n = 2). Five patients had familial thrombocytopenia. Six healthy children were studied as a reference. In the 19 thrombocytopenic patients, the platelets were significantly larger and % RP and TPO levels were significantly higher than those in the controls. Increased megakaryocytosis at diagnosis was associated with larger MPV and higher % RP but not with platelet level or TPO. The % RP was remarkably high in all ITP patients of group 1 indicating a brisk production of platelets despite low peripheral count. In all patients with familial thrombocytopenia, TPO was increased suggesting that the syndrome was not because of defective TPO production. The distribution of FcgammaRIIA alleles in the patients was similar to that in the controls. CONCLUSIONS: A combined application of % RP and TPO could be helpful in classifying patients with chronic thrombocytopenia into different categories. The observations may be of value in the clinical evaluation of ITP patients and lead to avoidance of invasive examinations at least in some patients.     

Serum thrombopoietin levels in relation to disease status in patients with immune thrombocytopenic purpura

Pre- and post-treatment serum thrombopoietin (TPO) concentration was measured in 35 patients with immune thrombocytopenic purpura (ITP). Mean post-treatment levels were significantly lower (P = 0.02) than pretreatment and not different for treatment modality. No significant correlation between pre- or post-treatment TPO and platelet counts was demonstrable (R = -0.325, P = 0.056 and R = -0.227, P = 0.190 respectively). In patients with very low platelet counts (< or =20 x 10(9)/l), pretreatment serum TPO was significantly higher than in patients with higher counts (P = 0.033). The logarithm of the platelet turnover rate, measured in 15 patients, correlated with pretreatment TPO levels (R = 0.64). These findings suggest a contributory role for TPO in the mechanism of ITP.     

Thrombopoietin is not uniquely responsible for thrombocytosis in inflammatory disorders

A few studies in patients with reactive thrombocytosis identified levels of the hormone higher than expected, and suggested that TPO behaves as an acute-phase protein and was responsible for increased platelet count. At the opposite, other studies did not find any significant rise of the hormone in patients who similarly developed reactive thrombocytosis. To gain further information on this topic, we compared TPO levels and platelet counts in two series of patients hospitalized for acute illnesses: one with strong elevation of both erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), and the other with normal values. Within the group of subjects with high ESR and CRP, 38 had normal platelet counts, while 15 had thrombocytosis. No thrombocytosis was observed in control patients. Patients with high acute phase indexes had significantly higher TPO levels and platelet counts than control patients. We identified significant positive correlations between ESR and CRP, and between TPO and CRP. Interestingly, no significant relationship between platelet counts and TPO levels was find. When we grouped patients with acute-phase reaction according to absence or presence of thrombocytosis, we found similar TPO values. Conversely, positive correlations between platelet count and IL-6 and between TPO and IL-6 have been identified. All together our results confirm that TPO acts as an acute phase protein but exclude the possibility that it is uniquely responsible for thrombocytosis of inflammatory disorders, which might recognize in IL-6 a credible candidate as a cooperating factor.     

High-dose intravenous immunoglobulin and splenectomy for the treatment of HIV-related immune thrombocytopenia in patients with severe haemophilia

Four patients with severe haemophilia A and one patient with severe Christmas disease developed severe immune thrombocytopenia (platelet count less than 20 x 10(9)/l). All five patients were HIV-antibody positive and one was HIV-antigen positive. Four patients were treated initially with prednisolone, but with only a transient platelet response in three and no response in the fourth. All patients were treated with high dose intravenous immunoglobulin (0.4 g/kg daily for 5 d) resulting in a rise in platelet count in all cases (range 138-300 x 10(9)/l) and then proceeded to splenectomy. Three remain in complete remission after 6-14 months, and one showed a good response with platelet counts ranging from 103 to 187 x 10(9)/l. The fifth patients achieved a normal platelet count for 3 months post-splenectomy, but suffered a relapse with platelet counts ranging from 25 to 108 x 10(9)/l over the next 3 years. However, following a severe Varicella infection 10 months ago, during which he developed a marked transient thrombocytosis, he has also maintained a normal platelet count.     

New insights into the thrombopoietic status of patients on dialysis through the evaluation of megakaryocytopoiesis in bone marrow and of endogenous thrombopoietin levels

The thrombopoietic status of patients with uremia remains unclear. This issue was addressed with particular reference to marrow megakaryocytopoiesis and endogenous thrombopoietin (TPO) levels. A study was conducted in 114 patients on hemodialysis, 43 patients on continuous ambulatory peritoneal dialysis, and 48 age-matched controls. Reticulated platelets, a marker of marrow megakaryocytopoiesis, were measured by flow cytometry. Serum TPO levels, platelet-associated IgG (PAIgG) levels, and hepatitis C virus (HCV) antibody titers were also measured by enzyme-linked immunosorbent assay. Circulating and reticulated platelet counts were significantly lower in the patients on dialysis than in the controls. Thrombocytopenia (less than 150 x 10(9)/L) was most frequent in the HCV-positive hemodialysis patients, who had a higher incidences and higher PAIgG titers. The following results were obtained in the HCV-negative dialysis patients: (1) platelet counts chronologically decreased with years on hemodialysis; (2) platelet counts were associated with the reticulated platelet counts; (3) serum TPO levels were significantly elevated in the dialysis patients, responding to the decrease of reticulated platelets; (4) hematocrits had a positive correlation with serum TPO levels, and serum TPO levels were significantly higher in the patients on hemodialysis who did not require recombinant human erythropoietin therapy than in the other patients. In conclusion, thrombocytopenia is a frequent finding in patients on dialysis. The failure of megakaryocyte production could be the principal cause of the platelet reduction, and the peripheral destruction and sequestration of platelets may be concomitantly involved. Elevation of serum TPO may in part serve as an aid to erythropoiesis in dialysis patients.     

Thrombopoietin serum levels in patients with aplastic anaemia: correlation with platelet count and persistent elevation in remission

In an attempt to evaluate the role of thrombopoietin (TPO) in the pathobiology of aplastic anaemia (AA), we have examined TPO levels in sera from 54 AA patients and 119 healthy controls. A total of 92 samples were collected from AA patients: 43 samples were harvested at diagnosis, 23 samples in the cytopenic period after treatment, and 26 samples when patients were in partial (n = 10) or complete remission (n = 16) following immunosuppressive treatment. TPO serum levels were assessed by a sandwich-antibody ELISA that utilized a polyclonal rabbit antiserum for both capture and signal. Serum samples from normal donors revealed a mean TPO level of 95.3 ± 54.0 pg/ml (standard deviation). Mean TPO levels in AA sera collected at diagnosis and before onset of treatment were 2728 ± 1074 pg/ml (P < 0.001 compared to normal controls; mean platelet count at that time: 27 × 10⁹/l). TPO serum levels of AA patients in partial or complete remission after immunosuppressive treatment were significantly lower than TPO levels at diagnosis (P < 0.001). However, despite normal platelet counts (mean 167 × 10⁹/l), TPO levels remained significantly elevated in complete remission (mean TPO 1009 ± 590 pg/ml, P < 0.001 compared to normal controls). There was a significant inverse correlation between serum TPO levels and platelet counts in AA patients who were not transfused for at least 2 weeks prior to sample collection (coefficient of correlation (r) = ?0.70, P < 0.0001). In summary, TPO levels were highly elevated in sera of patients with AA. Thus there is no evidence to suggest an impaired TPO response contributing to thrombocytopenia in AA. Thrombopoietin did not return to normal levels in remission, indicating a persisting haemopoietic defect in remission of AA. We hypothesize that elevated levels of TPO may be required to maintain normal or near normal platelet counts in remission of AA.     

Factors regarding increase of platelet counts in chronic hepatitis C patients with sustained virological response to interferon-Relation to serum thrombopoietin levels.

Thrombocytopenia is frequently found in patients with chronic liver disease, and associated with advanced fibrosis stage and with decreased liver function. Serum thrombopoietin (TPO) levels also decrease as the disease progresses from mild fibrosis to cirrhosis. On the other hand, platelet counts increase associated with improvement of fibrosis in chronic hepatitis C (CH-C) patients with sustained virological response (SVR) to interferon (IFN) therapy. Then, we studied if the increase of platelet counts in SVR associate with elevated TPO production or a reduction of spleen size. Liver fibrosis, spleen size, serum TPO levels, albumin, zinc turbidity test (ZTT), platelet counts were compared in fifteen CH-C patients with SVR before and after IFN therapy. Results: Albumin increased from 4.2+/-0.3 to 4.3+/-0.3g/dl (p=0.067), ZTT decreased from 17.7+/-5.9 to 8.9+/-3.9K-U (p<0.001), platelet counts increased from 15.5+/-6.8x10(4) to 19.9+/-5.8x10(4)/mul (p<0.01) and serum TPO levels increased from 1.65+/-0.94 to 2.06+/-1.22fmol/ml (p=0.073). Spleen size was measured by ultrasonography, and the spleen index was calculated by multiplication of the long and short axes from hilus, which decreased from 14.6+/-5.0 to 10+/-3.1 (p<0.001) after IFN therapy. In conclusion, increase of platelet counts in SVR may be related to the reduction of spleen size and increased serum TPO levels associated with improvement of fibrosis after IFN therapy.     

Measurement of endogenous plasma thrombopoietin in patients with acquired aplastic anaemia by a sensitive enzyme-linked immunosorbent assay

We measured the endogenous plasma concentration of thrombopoietin (TPO) in 76 patients with acquired aplastic anaemia (AA) by a sensitive sandwich enzyme-linked immunosorbent assay (ELISA). The plasma TPO concentrations were significantly higher in AA patients when compared to healthy control subjects ( P  < 0.0001) and there was a significant negative correlation between plasma TPO concentrations and platelet counts in 54 AA patients who had not received any platelet transfusions prior to sampling. On the other hand, there was no statistically significant correlation between the TPO concentrations and platelet counts in 22 AA patients who had previously received platelet transfusions.
We studied serial changes of plasma TPO concentration in 24 patients who showed an increase in their platelet counts following bone marrow transplantation or immunosuppressive (IS) therapy. Although a decrease in plasma TPO concentration was observed, levels remained above the range of normal healthy controls even in the patients who attained normal platelet counts following therapy. A decrease in TPO concentrations was observed in only half of the responders to IS therapy. Whether exogenous TPO will result in increased platelet counts in AA patients with high TPO levels remains to be determined.     

Thrombocytopenia in malaria.

The relationship between platelet counts and platelet bound (direct) or platelet directed (indirect) serum antibody concentrations was studied in 17 patients with Plasmodium falciparum malaria and 12 patients with P. vivax malaria. Platelet counts rose with recovery from infection from 196 +/- 84 x 10(9)/l (mean +/- SD) and 195 +/- 34 x 10(9)/l to 319 +/- 99 and 283 +/- 62 x 10(9)/l respectively (p less than 0.002), but there was no relationship between either absolute platelet count or changes in counts and either indirect or direct platelet antibody levels. These findings suggest that a non-immunologically mediated mechanism is involved in the pathogenesis of thrombocytopenia in malaria.     

Patients with thrombocytosis have normal or slightly elevated thrombopoietin levels

BACKGROUND AND OBJECTIVE: The distinction between clonal and reactive thrombocytoses is a frequent problem and implies different therapeutic options. As thrombopoietin (TPO) is the main regulator of megakaryocytopoiesis and thrombopoiesis, we measured TPO levels in patients with thrombocytosis in an attempt to understand the regulation and potential utility of distinguishing thrombocytoses. DESIGN AND METHODS: Serum TPO levels, platelet counts, mean platelet volume, hemoglobin, erythrocyte sedimentation rate and age were evaluated in 25 patients with clonal thrombocytosis (15 with essential thrombocythemia, 6 with polycythemia vera and 4 with chronic myeloid leukemia) and in 50 patients with reactive thrombocytosis distributed in three groups: 1) patients in post-surgical states; 2) patients with solid tumors; and 3) patients with inflammatory diseases. RESULTS: TPO levels were slightly increased in patients with clonal (135+/-50 pg/mL) and reactive (147+/-58 pg/mL) thrombocytosis compared with controls (121+/-58 pg/mL). Analyzing the different groups, patients with essential thrombocythemia had the lowest TPO levels (120+/-28 pg/mL) and patients with solid tumors the highest levels (162+/-59 pg/mL). Patients with clonal thrombocytosis were older, had higher platelet counts, mean platelet volume and hemoglobin, and lower erythrocyte sedimentation rate than patients with reactive thrombocytosis. INTERPRETATION AND CONCLUSIONS: Minor differences were observed in TPO levels between patients with primary and secondary thrombocytoses. Erythrocyte sedimentation rate, but not TPO levels, may be a useful tool for discriminating both types of thrombocytoses.     

Serum thrombopoietin and erythropoietin levels in patients with acute promyelocytic leukaemia during all-trans retinoic acid treatment

Endogenous serum thrombopoietin (TPO) and various cytokines including erythropoietin (EPO), interleukin (IL)-3, IL-6, IL-11, granulocyte-colony stimulating factor (G-CSF), granulocyte-macrophage-colony stimulating factor (GM-CSF) and stem cell factor (SCF) levels were measured in five patients with acute promyelocytic leukaemia (APL) during all-trans retinoic acid (RA) treatment. During differentiation-inducing therapy, platelet counts slowly increased and reached a peak between days 29 and 46 (median day 35). Serum TPO levels increased parallel to the increasing platelet counts and reached a maximum level during the first 10-20 d of all-trans RA treatment. The circulating TPO levels then decreased in inverse correlation to the platelet counts. These unique changes in serum TPO levels revealed that TPO levels were not regulated by platelet or megakaryocyte mass in patients with APL during differentiation-inducing therapy, and it would appear that TPO levels are directly regulated by all-trans RA during the first 10-20 d of treatment. In addition, the change in circulating EPO levels and reticulocyte counts were similar to that of the TPO levels and platelet counts during all-trans RA treatment, suggesting a close relationship between TPO and EPO signalling.     

Kinetics of CFU-Mk after automated plateletpheresis

BACKGROUND AND OBJECTIVES: Platelet count, thrombopoetin (TPO) level and the compartment of megakaryocyte progenitor cells (CFU-Mk) are major determinants in the regulation of thrombopoiesis. The aim of this study was to investigate the potential changes in the compartment of CFU-Mk and their correlation with serum TPO levels and platelet count after plateletpheresis. MATERIALS AND METHODS: Twelve healthy individuals were randomly assigned to undergo single-donor plateletpheresis. A collagen-based in vitro culture system was used to determine the number of peripheral blood (PB) CFU-Mk before and after donation and on days 1, 4 and 7 thereafter. TPO levels were measured by a specific enzyme-linked immunosorbent assay and whole blood counts were performed using an automated cell counter. RESULTS: The pre-apheresis platelet count (mean +/- SEM: 276 +/- 13 x 10(9)/l) decreased after plateletpheresis to a nadir of 194 +/- 8 x 10(9)/l (P < 0.001), showed a gradual increase on days 1 and 4, and reached pre-apheresis values by day 7 (280 +/- 11). The serum TPO levels were found to be significantly increased on days 1 and 7 as compared to baseline levels (baseline value 103.3 +/- 18.5 pg/ml versus day-1 value 135.8 +/- 25.8 pg/ml and day-7 value 132 +/- 30.19 pg/ml; P < 0.03 and P < 0.03, respectively). The numbers of CFU-Mk in PB were significantly elevated on day 4 only (125 +/- 21 colonies/ml of PB versus pre-apheresis values of 68 +/- 18 colonies/ml of PB, P < 0.005). CONCLUSIONS: These findings suggest that platelet loss during plateletpheresis affects thrombopoiesis at the progenitor cell level, probably through alterations in TPO plasma concentrations.