Soluble c-kit molecule in serum from healthy individuals and patients with haemopoietic disorders

Summary The proto-oncogeae, c-kit , encodes a transmembrane tyrosine kinase receptor (KIT) and plays an important role in haemopoiesis. We have identified a 95kD soluble form of KIT (S-KIT) in culture supernatant of human megakaryoblastic cell line, CMK. To study the physiological significance of S-KIT, we have established a sensitive sandwich ELISA system. Serum samples from healthy individuals contained detectable amounts of S-KIT. Next, we determined a total of 220 samples from 134 patients with haemopoietic disorders. A considerable number of patients with acute myeloid leukaemia (AML), especially those with more immature phenotypes (MO, Ml or M2) had elevated levels of serum S-KIT. Those levels decreased to the normal range after effective chemotherapy. In chronic myeloid leukaemia, patients with myeloid blastic crisis showed markedly elevated levels of serum S-KIT. In contrast, S-KIT levels decreased in cases with either acute or chronic lymphoid leukaemia. There was a tendency for patients with severe aplastic anaemia to show decreased levels, but it was not significant. In myelodysplastic syndrome, S-KIT levels appeared to vary by subsets, with higher concentration in more advanced forms of the disease. Although the functional role of S-KIT is not yet elucidated, these results suggest that the serum S-KIT levels may reflect the pathological states of various haematological disorders.     

A sensitive sandwich ELISA for measuring erythropoietin in human serum

A sandwich, non-competitive enzyme-linked immunosorbent assay (ELISA) for erythropoietin (EPO) is described. The ELISA utilizes a monospecific, polyclonal antibody raised in rabbits against human recombinant EPO (rhu EPO) and purified over a rhu EPO affinity chromatography column. The ELISA procedure can be summarized as follows: Anti-EPO is coated onto 96-well ELISA microtitre plates; standard EPO or sample is added and left to bind to this catching antibody; this is followed by the addition of the same antibody which has been biotinylated; finally, anti-biotin conjugated to alkaline phosphatase is added and the enzyme reaction developed and read at 405 nm. All parameters of the assay have been optimized. Recombinant human EPO was standardized against the World Health Organization 2nd International Reference Preparation for erythropoietin. The minimal detectable concentration of rhu EPO was 0.3-0.5 mU/ml, which corresponded to 1.2-2 mU/ml of EPO in serum (serum diluted 1:4). No reaction was obtained with a variety of blood components and cytokines, indicating that the anti-EPO antibody did not cross-react with those substances to produce false-positive results. The intra-assay variation ranged from 3% to 10%, while the inter-assay variation ranged from 8.5% to 24%. Serum dose-response curves were parallel to the standard dose-response curve. The assay is easy to use, rapid, reproducible, but above all quantitative, specific and sensitive to measure the EPO content in all serum samples.     

A family with hereditary thrombocythaemia and normal genes for thrombopoietin and c-Mpl

Hereditary thrombocythaemia (HT) is an inherited autosomal dominant disorder. Recent studies reported six different mutations, four within the thrombopoietin (TPO) gene and two within c-Mpl (TPO receptor) gene in six unrelated families with HT. This study investigated the molecular basis of hereditary thrombocythaemia in an Israeli-Jewish family. We screened the genes for TPO and c-Mpl by amplification and sequencing of all the corresponding exons including exon/intron boundaries and promoters. In addition, plasma levels of TPO and erythropoietin (EPO) were measured. No abnormality in the TPO/c-Mpl genes has been identified in affected HT family members. Plasma TPO and EPO levels were found to be normal/low or normal respectively in the individuals affected. In conclusion, lack of a molecular lesion within either TPO or cMpl genes indicate that HT may be caused by factors other than TPO-cMpl axis in this family.     

Age-related changes in thrombopoietin in children: reference interval for serum thrombopoietin levels

We studied thrombopoietin (TPO, Mpl ligand) values using a sensitive ELISA in 254 serum samples obtained from disease-free children and adult volunteers. TPO was detected in all samples, and its values ranged widely from 0.25 to 9.18 fmol/ml. When analysed by dividing the subjects into 11 age groups, the mean TPO levels from birth to 1 month of age were increased (3.73-5.92 fmol/ml). The highest values were found 2 d after birth; TPO levels then gradually decreased to adult levels (0.83 fmol/ml). The relationship between TPO values and platelet counts was not significant in all subjects (r = 0.27) or in children alone (r = 0.12). In children > 1 month of age a 95% reference interval for serum TPO values was determined from 0.58 to 3.27 fmol/ml. A significant correlation was found between TPO values in serum and plasma; serum TPO values = -0.257 + 4.039 x plasma TPO values (r = 0.951, P < 0.001, n = 22). This study is the first to report age-dependent changes in blood TPO levels throughout child development. Serum TPO values were significantly high up to 1 month of age and were correlated with plasma TPO levels.     

肝硬化患者血清血小板生成素水平的测定及临床意义

探讨肝硬化患者血清血小板生成素(TOP)浓度与血小板减少的关系。用酶联免疫吸附法(ELISA)测定肝硬化肝功能代偿期、失代偿期以及正常人血清TPO浓度。血清TOP浓度正常人、肝硬化肝功能代偿期、失代偿期分别为(136.24±68.56)pg.m l-1、(124.34±41.31)pg.m l-1和(59.05±52.77)pg.m l-1。肝硬化肝功能失代偿期的血清TPO浓度较正常人明显降低(t=4.04,P<0.001);正常人的血清TPO浓度受外周血小板计数的调节,而肝硬化患者的血清TPO浓度与外周血小板计数之间无明显相关而与血清白蛋白浓度呈正相关(r=0.86,P<0.001)、血清总胆红素浓度呈负相关(r=0.49,P<0.05)。肝细胞产生TPO不足可能是肝硬化发生血小板减少的主要原因。血清TPO浓度可能是评价肝硬化患者肝功能的有用指标。     

Serum thrombopoietin levels in patients with aplastic anaemia

Endogenous serum thrombopoietin (TPO) levels were measured in 31 patients with aplastic anaemia (AA) using an enzyme immunoassay with a sensitivity of 20 pg/ml. The median platelet count for all AA patients was 30 ± 29 × 10⁹/l (range 5–102) compared with a median of 284 ± 59 × 10⁹/l (range 148–538) for normal controls. Serum TPO levels were significantly elevated in all patients compared with normals (1706 ± 1114.2, range 375–5000 v 78 ± 54, range 16.5–312.9, P  < 0.0001). There was no correlation between serum TPO levels and the degree of thrombocytopenia in AA patients, but TPO levels were significantly higher in patients who were platelet transfusion dependent than in patients who were transfusion independent ( P  < 0.01). There was a trend for higher TPO levels in patients with severe AA compared with non-severe AA patients. Clinical trials of TPO and a related truncated, pegylated molecule, megakaryocyte growth and development factor (PEG-rHuMGDF), are awaited to determine whether treatment with these drugs will result in increased platelet counts in patients with AA.     

Plasma thrombopoietin levels in liver cirrhosis and kidney failure

BACKGROUND: Recently, c-Mpl ligand (thrombopoietin, TPO) has been cloned by several groups and found to be a primary regulator of thrombopoiesis. Its mRNA expression has been detected in several organs including kidneys, bone marrow stroma cells, muscles, and is very strongly expressed in the liver. OBJECTIVE: To clarify thrombopoiesis and the regulation of TPO in severe liver and renal failure. DESIGN: We analysed plasma TPO levels in patients with biopsy verified liver cirrhosis (n = 18; mean platelet count 115 +/- 54 x 109 L-1), in patients on chronic haemodialysis as a result of end-stage renal failure (n = 20; mean platelet count 295 +/- 94 x 109 L-1), and in healthy individuals (n = 20; mean platelet count 250 +/- 40 x 109 L-1). Plasma was prepared from EDTA-anticoagulated whole blood and a commercially available ELISA kit was used for the analysis. RESULTS: The mean plasma TPO concentration amongst the normal individuals was 50 +/- 14 pg mL-1. In the patients with liver cirrhosis and in patients on haemodialysis the mean TPO levels were 62 +/- 19 pg mL-1 and 46 +/- 17 pg mL-1, respectively. The mean plasma TPO concentration for the cirrhotic patients was significantly higher than the mean recorded for the healthy volunteers (P = 0.031), whereas no statistically significant differences in plasma TPO were seen between the group of end-stage renal failure and normals. CONCLUSION: Our results suggest that TPO production is maintained in liver cirrhosis and in renal failure, and that the thrombocytopenia in liver cirrhosis is not due to an impaired TPO production.     

Pharmacokinetics of pegylated recombinant human megakaryocyte growth and development factor in healthy volunteers and patients with hematological disorders

OBJECTIVES: The purpose of this study is to examine the pharmacokinetics of pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) in healthy volunteers with normal hematopoiesis and patients with idiopathic thrombocytopenic purpura (ITP), acute myeloid leukemia (AML), myelodysplastic syndromes (MDS), and aplastic anemia (AA). METHODS: PEG-rHuMGDF was intravenously administered to healthy volunteers and patients with ITP, AML, MDS, and AA. The serum concentration of PEG-rHuMGDF was measured and the pharmacokinetics was investigated using non-linear mixed-effects modeling technique. RESULTS: The systemic clearance (CL) and volume of distribution at steady-state (Vss) consistently decreased in the healthy subjects, when the dose increased. In AML patients, CL and Vss decreased when the dose increased, but the change of CL was not statistically significant. In contrast, no significant dose dependency of these parameter estimates was observed in MDS patients. In AA patients there was no significant change in Vss but the CL of the higher dose groups was slightly smaller than that of the lower dose groups. Relatively smaller CL and Vss in ITP patients than those of healthy volunteers at the same dose were observed. CONCLUSIONS: This saturable pathway of CL may involve the receptor-mediated endocytosis and degradation by megakaryocyte lineage cells and platelets. The saturable distribution space can be also explained by the receptors on hematopoietic cells. The non-saturable distribution space corresponds to the value of plasma and interstitial fluid volume.     

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.     

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.     

Interferon increases serum thrombopoietin in patients with chronic hepatitis C

We measured serum thrombopoietin (TPO) in chronic hepatitis C treated with interferon (IFN). The platelet count before the therapy was 161.9 ×10⁹ ± 64.1 × 10⁹/l, which decreased to 116.3 × 10⁹ ±  48.4 × 10⁹/l 1 week after IFN therapy ( P  <0.01). On the other hand, serum TPO increased from 1.96 ± 0.60 fmol/ml to 2.68 ± 0.69 fmol/ml ( P  < 0.02). Contrary to a recent report that serum TPO was not altered in liver cirrhosis, these data indicate that serum TPO was increased in chronic hepatitis C in response to thrombocytopenia by IFN therapy.     

Serial serum thrombopoietin levels in a pregnant woman with essential thrombocythaemia

Thrombopoietin (TPO) is a ligand for c-mpl, which regulates the differentiation and maturation of megakaryocytes. Essential thrombocythaemia (ET) is a clonal myeloproliferative disorder. It has been reported that the platelet count declines during pregnancy in ET patients. We examined serial changes in the serum TPO level during the course of pregnancy in a patient with ET. The serum TPO level showed significant negative correlation with the platelet count. Although it mimicked the normal feed back system, the TPO levels were consistently higher than the normal upper limit. Accumulation of these data will be helpful in revealing the pathogenesis of ET and the decline in the platelet count during pregnancy.     

Plasma thrombopoietin (TPO) levels and expression of TPO receptor on platelets in patients with myelodysplastic syndromes

Data on endogenous thrombopoietin (TPO) levels and their regulation in myelodysplastic syndromes (MDS) are sparse. We examined the plasma TPO level of 85 MDS patients by a sensitive enzyme immunoassay and the platelet expression of TPO receptor (TPO-R) protein, which metabolizes endogenous TPO, in 19 MDS patients with an equilibrium binding assay using ¹²⁵I-TPO. The MDS patients had higher plasma TPO levels (7.0 ± 9.3 fmol/ml) than 52 normal subjects ( P < 0.0001). Refractory anaemia (RA) patients ( n  = 39) had higher plasma TPO levels than patients ( n  = 28) with RA with excess blasts (RAEB) or RAEB in transformation (RAEB-t) ( P  = 0.0002), irrespective of similar platelet counts in these groups. The plasma TPO level correlated inversely with the platelet count in RA patients ( P  = 0.0027) but not in RAEB and RAEB-t patients ( P  = 0.7865). These data suggest that the physiological pathway for TPO production and metabolism is conserved, at least partially, in RA, but deranged in RAEB/RAEB-t. The number of TPO-R per platelet was significantly smaller in 19 MDS patients (17.5 ± 13.3) than in normals ( P  = 0.0014), but similar between RA patients and patients with RAEB and RAEB-t. Further, the bone marrow megakaryocyte count, determined in 31 MDS patients, was quite similar between RA patients and patients with RAEB or RAEB-t. Thus, in addition to thrombocytopenia, a reduced platelet TPO-R number may contribute to elevated plasma TPO levels in MDS, and a regulatory pathway for circulating TPO other than platelet TPO-R and marrow megakaryocytes, such as blasts expressing TPO-R, may operate in RAEB/RAEB-t.     

Spontaneous and cytokine-induced thrombocytopenia in myelodysplastic syndromes: serum thrombopoietin levels and bone marrow morphology

Thrombocytopenia is a substantial clinical problem for patients with myelodysplastic syndromes (MDS). Cytokine treatment for granulocytopenia and anaemia may further reduce the platelet counts. We studied serum thrombopoietin levels (S-TPO) in 52 patients with MDS and 96 healthy controls and related the results to clinical and morphological variables. S-TPO was also assessed after treatment with granulocyte-CSF (G-CSF) and erythropoietin (EPO) in 30 of these patients. S-TPO in MDS was not a normally distributed variable; mean value was 394 pg/ml, SD +/-831 and median value 123 (12-5000 pg/ml). The controls showed lower S-TPO levels than the patients (median 78 pg/ml, P = 0.003) whereas no differences between the MDS subgroups were observed (P = 0.86). Patients with ringed sideroblastic anaemia (RARS) showed the highest platelet counts and higher S-TPO levels than the controls (P = 0.005). No association between platelet counts and S-TPO levels was found in the patients (P = 0.67). TPO levels were generally low in patients with refractory anaemia with an excess of blasts (RAEB), but very high levels were found in five patients. Patients with a high transfusion need had higher S-TPO levels, whereas bone marrow blast counts, cellularity or megakaryocytes showed no correlation with S-TPO. Patients with 5q- showed lower TPO levels than the other patients, indicating that thrombopoietin is not a mediator of thrombocytosis in these cases. Treatment with G-CSF + EPO significantly reduced the platelet counts (P = 0.0002), but this change was not related to significant changes in S-TPO levels or morphology. Patients with RARS and thrombocytosis who normalized their platelet counts showed a concomitant reduction in S-TPO. This may suggest that the increased platelet counts observed in RARS may be caused by increased S-TPO levels. In conclusion, our study shows that platelet, megakaryocyte and thrombopoietin regulation is rather complex in myelodysplastic syndromes and that spontaneous or induced thrombocytopenia are not usually mirrored by increased S-TPO levels.     

Thrombopoietin and its receptor expression in pediatric patients with chronic immune thrombocytopenia

Objectives: Chronic immune thrombocytopenia (cITP) is common in children. However, the pathogenesis has not been fully elucidated. This study aimed to determine whether thrombopoietin (TPO) and its receptor c-mannosylation of the TPO receptor (c-Mpl) have an impact on childhood cITP.

Methods: Sixty-four patients with newly diagnosed ITP (nITP), 64 patients with persistent ITP, 80 patients with cITP, and 64 healthy children (control) were enrolled in this study. Plasma TPO was measured with an ELISA, and c-Mpl was determined by flow cytometry.

Results: Plasma TPO levels showed differences among the four groups (p?=?0.001). TPO levels in the cITP group were significantly decreased compared to those in the nITP group (p?p?=?0.0275). c-Mpl MFI was lower in the cITP group than in the nITP group(p?p?p?=?0.023). The control group, compared with the other groups, had lower levels of c-Mpl mRNA.

Conclusions: The expression of TPO and c-Mpl was significantly decreased in the cITP group compared to the nITP group, suggesting that TPO and its receptor may play important roles in childhood cITP pathogenesis.     

The platelet thrombopoietin receptor number and function are markedly decreased in patients with essential thrombocythaemia

Essential thrombocythaemia (ET) is a relatively common myeloproliferative disorder characterized by an elevated platelet count. As thrombopoietin (TPO) and the TPO receptor (c-mpl) regulate platelet production in normal physiology, their role in ET was investigated. A well-characterized cohort of 23 ET patients was evaluated and followed for 3 years. The TPO levels in these ET patients (189 +/- 131 pg/ml) were the same as in normal subjects (179 +/- 112 pg/ml) and TPO was not produced by ET platelets. There were 5.6 +/- 5.5 TPO binding sites/ET platelet vs. 56 +/- 17 TPO binding sites/normal platelet and this was associated in ET patients with normal-sized platelet c-mpl protein and mRNA, but a 10-fold reduction in platelet c-mpl mRNA. The K(d) for the TPO receptor on ET platelets was 66 +/- 30 pmol/l vs. 163 +/- 31 pmol/l on normal platelets, but the c-mpl cDNA had a normal nucleic acid sequence. The decreased number of ET platelet TPO receptors resulted in a fourfold decrease in the platelet-dependent TPO clearance (0.30 +/- 0.14 ml/h/10(9) ET platelets vs. 1.24 +/- 0.38 ml/h/10(9) normal platelets) at a time when the platelet count in ET patients was 2.7-fold above normal. The fourfold decrease in the TPO clearance, elevated platelet mass and resulting normal total TPO clearance explain the normal TPO levels. These results also suggest that the thrombocytosis in ET may be attributed to an alteration of the normal feedback interaction between TPO and its receptor and not as a result of any defect in the structure of TPO or c-mpl.     

Autoantibodies to thrombopoietin and the thrombopoietin receptor in patients with immune thrombocytopenia

Autoantibodies to thrombopoietin (TPO, also termed THPO) or the TPO receptor (cMpl, also termed MPL) could play a pathological role in immune thrombocytopenia (ITP). In this study, we tested for autoantibodies against TPO, cMpl, or the TPO/cMpl complex in ITP and other thrombocytopenic disorders. Using an inhibition step with excess TPO in fluid‐phase to improve binding specificity, the prevalence of anti‐TPO autoantibodies was: active ITP: 9/32 (28%); remission ITP: 0/14 (0%); non‐immune thrombocytopenias: 1/10 (10%); and healthy controls: 1/11 (9%). Similarly, using an inhibition step with excess cMpl, the prevalence of specific anti‐cMpl autoantibodies was: active ITP: 7/32 (22%); remission ITP: 1/14 (7%); non‐immune thrombocytopenias: 3/10 (30%); and healthy controls: 0/11 (0%). Two active ITP patients had autoantibodies against the TPO/cMpl complex, but not against TPO or cMpl alone. Anti‐TPO or anti‐cMpl autoantibodies were found in 44% of ITP patients, and in 40% of patients with other thrombocytopenic disorders. These autoantibodies did not correlate with ITP disease severity or number of ITP treatments received; however, in this cohort, 3 patients failed to respond to TPO receptor agonist medications, and of those, 2 had anti‐TPO autoantibodies. This suggests that anti‐TPO and anti‐cMpl autoantibodies are associated with thrombocytopenia, and may be clinically relevant in a subset of ITP 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 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.     

Serum thrombopoietin levels in thrombocytopenic and non-thrombocytopenic patients with human immunodeficiency virus (HIV-1) infection.

HIV-1 seropositive patients often exhibit thrombocytopenia, considered of multifactorial aetiology. Thrombopoietin (TPO), a recently isolated cytokine, is the main regulator of megakaryocyte and platelet production. The objective of this study was to analyse serum TPO levels in thrombocytopenic and non-thrombocytopenic HIV-1 infected patients. Serum TPO levels were measured by ELISA in 43 healthy individuals and in 88 HIV-1 infected patients: 68 thrombocytopenics and 20 non-thrombocytopenics. Thrombocytopenic HIV-1 infected patients showed higher TPO concentrations (263 +/- 342 pg/ml) than non-thrombocytopenics (191 +/- 86 pg/ml); levels in both groups were significantly higher than those of healthy controls (121 +/- 58 pg/ml). Two subgroups of thrombocytopenic patients, the autoimmune thrombocytopenic purpura (AITP) group and the mild thrombocytopenic group, presented TPO levels similar to those of non-thrombocytopenics. Patients exhibiting pancytopenia showed the highest TPO concentrations. However, there was no correlation between TPO levels and platelet counts in any group of HIV-1 infected patients. TPO levels in HIV-1 seropositive patients were slightly increased and the differences in TPO levels between thrombocytopenic and non-thrombocytopenic patients were generally small. The finding of mildly increased TPO levels along with the recently described recovery of thrombocytopenia following recombinant TPO administration confirms the implication of ineffective platelet production in the origin of HIV-associated thrombocytopenia.