Circulating thrombopoietin level in chronic immune thrombocytopenic purpura

The circulating thrombopoietin (TPO) level in 43 patients with chronic immune thrombocytopenic purpura (ITP) was examined by an ELISA system. The TPO level (mean±SD) in ITP patients was mildly elevated (1.86±1.17 fmol/ml) compared to that in normal subjects (0.76±0.21), and was within the normal range in 30% of ITP patients. In contrast, the TPO level in patients with aplastic anaemia was very high, 12.35±6.42 fmol/ml. There was no correlation between TPO level and platelet count in ITP patients. Splenectomy was performed in two ITP patients, after which platelet counts increased to normal levels and TPO levels showed a transient increase. These data suggest that reactive TPO production against thrombocytopenia in ITP is small when compared to that in aplastic anaemia. Relative endogenous TPO deficiency may play some role in the pathophysiology of thrombocytopenia in ITP patients.     

Quantitation of platelet-associated IgG by radial immunodiffusion

Platelet-associated IgG (PAIgG) was measured by a simple radial immunodiffusion technique using washed solubilized platelets and commercially available immunoplates. Subjects with normal platelet counts had PAIgG levels of 1.5--7.0 fg/platelet. Subjects with idiopathic immune thrombocytopenic purpura (ITP) had levels ranging from 5.7 to 70.5 fg/platelet. All patients with recurrent ITP and 85% of patients with acute ITP had elevated PAIgg. Elevated PAIgG was also found in 17% of patients with recovered ITP, 40% of patients with SLE and thrombocytopenia, 57% of patients with thrombocytopenia occurring during the course of septicemia, and 100% of patients with IgG myeloma in whom the serum IgG level was clearly elevated, regardless of the platelet count. The results are similar to reports that used more complex techniques.     

Human thrombopoietin levels are high when thrombocytopenia is due to megakaryocyte deficiency and low when due to increased platelet destruction

Thrombopoietin (TPO), the ligand for c-mpl, stimulates proliferation of committed megakaryocytic progenitors and induces maturation of megakaryocytes. To better understand factors regulating TPO levels, we measured blood levels of TPO in patients with impaired platelet production due to aplastic anemia (AA) and with platelet destructive disorders, including idiopathic thrombocytopenic purpura (ITP), posttransfusion purpura (PTP), drug purpura (DP), and X-linked thrombocytopenia (XLTP). The TPO receptor capture enzyme immunoassay (EIA) used had a detection limit of integral of approximately-150 to 200 pg/mL. TPO was undetectable in 88 of 89 normal individuals. Eighteen of 19 patients with AA and a mean platelet count (MPC) of 18,000/microliters (2,000 to 61,000/microliters) had markedly elevated TPO levels (mean, 1,467 pg/mL; range, 597 to 3,834 pg/mL). Eight AA patients who responded to immunosuppressive therapy with their MPC increasing to 140,000/microliters (92,000 to 175,000/microliters) had substantial decreases in TPO (mean, 440 pg/mL; range, 193 to 771 pg/mL). Initial TPO levels did not differ significantly between responders and nonresponders. In contrast, all 21 patients with ITP and an MPC of 16,000/microliters (1,000 to 51,000 /microliters) had undetectable TPO levels, as did 6 patients with acute PTP or DP and 2 patients with XLTP. Megakaryocyte mass, reflected in the rate of platelet production, appears to be the major determinant of TPO levels in thrombocytopenic patients rather than circulating platelet levels per se. Measurement of serum TPO may be useful in differentiating thrombocytopenias due to peripheral destruction from those due to thrombopoietic failure.     

High serum levels of granulocyte-macrophage colony-stimulating factor in patients with liver cirrhosis and granulocytopenia

Summary Leucopenia is often observed in patients with liver cirrhosis. We measured levels of serum granulocyte-macrophage colony-stimulating factor (GM-CSF) in patients with liver cirrhosis by a sensitive enzyme linked immunosorbent assay. Eight out of 22 patients with liver cirrhosis had detectable serum GM-CSF (range, 55 to 245 pg/ml:mean, 135 pg/ml). Serum GM-CSF was detected in all patients with a granulocyte count below 2.0 × 10⁹/l, but in only one patient with a granulocyte count above 2.0 × 10⁹/l. Haemoglobin concentration, platelet count, serum albumin, total bilirubin and aminotransferase levels did not correlate with serum GM-CSF levels. These findings may reflect a feedback mechanism between the number of circulating granulocytes and serum GM-CSF levels in patients with cirrhosis.     

High-dose intravenous gammaglobulin (IVG) in neonatal immune thrombocytopenia

Recent reports suggest that intravenous gammaglobulin (IVG) may be an effective treatment modality in patients with immune thrombocytopenia (ITP). Two newborns with isoimmune thrombocytopenia secondary to HLA-A2 and PLA1 platelet antigen incompatibilities with their respective mothers and two newborns with thrombocytopenia secondary to maternal ITP were treated with IVG 400 mg/kg/day x 5 days. One patient was exposed to steroids in utero; only one mother was thrombocytopenic at the time of delivery. All patients were severely thrombocytopenic on day 1 of treatment with mean platelet count of 5.7 x 10(9)/L. All had petechiae and positive quaiac stools, and patients with isoimmune thrombocytopenia had CT scan evidence of intracranial bleeds. The mean platelet count after 24 hr was 26.7 x 10(9)/L and the average platelet increase was 21 x 10(9)/L and 33 x 10(9)/L at 24 and 48 hr, respectively. The two cases with isoimmune thrombocytopenia had sustained platelet increases; the two cases secondary to maternal ITP had transient platelet elevations. IVG can rapidly elevate the platelet count in these patients, especially those with severe bleeding manifestations.     

Serum levels of thrombopoietin, IL-11, and IL-6 in pediatric thrombocytopenias

 We measured serum levels of thrombopoietin (TPO), interleukin (IL)-11, and IL-6 in 90 different samples from 67 pediatric patients with thrombocytopenia (TP). The cytokine levels were determined by enzyme-linked immunosorbent assays (ELISA), and the biological activity of TPO was measured using a cell line transfected with human c-mpl. In patients with impaired megakaryocytopoiesis, as found in diseases such as aplastic anemia, amegakaryocytic TP, or TP with absent radii, we found TPO levels which were highly elevated compared with normal values (mean=261 AU/ml, n=52, vs. 22 AU/ml in healthy controls). In contrast, patients suffering from idiopathic thrombocytopenic purpura (mean=16 AU/ml, n=31) or platelet function defects (mean=23 AU/ml, n=7) demonstrated normal TPO levels. The biological activity tested in the bioassay correlated well with the ELISA data. However, sera of some patients with amegakaryocytic TP demonstrated a remarkably higher biological activity of TPO than expected from the ELISA data. Within the different groups there was no correlation between platelet counts and TPO levels. Only 27% of all samples had elevated levels of IL-11 (mean=450 pg/ml, n=20). Elevated IL-6 serum levels were detected in only 13% of all samples analyzed (mean=42 pg/ml, n=12). We conclude that megakaryocytopoiesis is regulated mainly by TPO, that it is dependent on the platelet and the megakaryocytic mass, and that IL-11 plays an additional role in supporting the platelet production. IL-6 does not appear to be up-regulated in children with thrombocytopenia. Received: November 19, 1998 / Accepted: April 9, 1999     

Contribution of interleukin 27 serum level to pathogenesis and prognosis in children with immune thrombocytopenia

Concepts surrounding the mechanisms of thrombocytopenia in ITP have shifted from the traditional view of autoantibody mediated platelet destruction to more complex mechanisms in which impaired platelet production, T-cell-mediated effects, and disturbed cytokine profiles play a role. Interleukin 27 (IL-27) plays pleiotropic roles in immunomodulation and autoimmune diseases.We aimed to determine the level of IL-27 in patients with ITP and its relationship to patient and disease characteristics as well as disease chronicity and response to treatment.Sixty childrens with primary immune thrombocytopenia were consequetively enrolled in this study as well as 20 age and sex matched healthy controls.ITP patients had significantly higher levels of IL-27 than controls (770.6 and 373.8 pg/ml, respectively). Patients with acute ITP had the highest levels of IL-27 among patient groups, while patients in remission had the lowest IL-27 levels (860.1and 622.9 pg/ml, respectively). Patients who received IVIG and combined steroids plus IVIG had significantly higher IL-27 levels than others. Patients who received Eltrombopag had significantly lower IL-27 levels than others.IL-27 seems to play a role in pathogenesis of childhood ITP. IL-27 can be used as a predictor for disease occurrence as well as responsiveness to treatment.     

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     

Immune thrombocytopenic purpura: autoimmune or immune complex disease?

To assess the pathogenic role of circulating immune complexes (CIC) in idiopathic thrombocytopenic purpura (ITP), 39 patients with ITP were compared to 17 patients with other forms of thrombocytopenia (hypersplenism (N = 12), impaired thrombopoiesis (3), thrombocytopenia of unknown origin (2)) and six nonthrombocytopenic subjects. In all patients, platelet mean life span (MLS), platelet associated IgG (PAIgG), as well as circulating anti-platelet antibodies and C1q binding activities were determined. In most cases, immune complex solubilization capacity (ICSC) and immune complex precipitation inhibition capacity (ICPIC) of sera were also assessed. All patients with ITP had a reduced platelet MLS, but PAIgG was elevated in only 16 out of 24 patients with chronic ITP, in six out of 10 patients with acute ITP and in four out of five patients with secondary ITP. In the group of patients with thrombocytopenia due to splenomegaly, seven out of 12 patients had elevated PAIgG while the platelet MLS was only slightly reduced. Of the 39 patients with ITP only one with secondary ITP had C1q binding material in his serum, as opposed to six out of 12 thrombocytopenic patients with splenomegaly. Whereas only three patients with ITP had abnormal immune-complex modulating capacities, such deviations were found in seven out of 12 patients with thrombocytopenia due to splenomegaly. We conclude that our data render the role of CIC in the pathogenesis of ITP very questionable.     

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.     

Serum thrombopoietin levels and anti-thrombopoietin antibodies in systemic lupus erythematosus

Thrombocytopenia is a common phenomenon in patients suffering from systemic lupus erythematosus (SLE). The cause of thrombocytopenia in SLE, however, is poorly understood. In this study, 100 patients with SLE were evaluated for serum thrombopoietin levels, anti-thrombopoietin antibodies and routine laboratory parameters such as peripheral blood counts, parameters of blood chemistry and immunologic parameters of SLE. The median platelet count of SLE patients was 230 g/l and 19 were thrombocytopenic (range 8-148 g/l). Thrombopoietin levels in SLE patients were found to be significantly higher than in healthy controls (n = 96; median, 117 pg/ml vs 64 pg/ml, P < 0.01). When excluding thrombocytopenic SLE patients, thrombopoietin levels in SLE were still above controls (111 pg/ml, P < 0.01). The thrombopoietin levels were correlated to erythrocyte sedimentation rate and ECLAM score of disease activity, and inversely correlated to complement factor C4, but not to the platelet count. Anti-thrombopoietin antibody reactivity was found in 23% of SLE patients. Interestingly, these patients had lower platelet counts than SLE patients without anti-thrombopoietin antibodies (median 174 g/l and 253 g/l, respectively, P < 0.01), but thrombopoietin levels were not significantly different. Taken together, thrombopoietin levels are significantly higher in the sera of SLE patients than in healthy controls and anti-thrombopoietin antibodies are frequently found.     

Reduced transforming growth factor-beta1 production by mononuclear cells from patients with active chronic idiopathic thrombocytopenic purpura

Chronic idiopathic thrombocytopenic purpura (ITP) is an autoimmune disorder in which activated T-helper (Th) cells and different Th-cell cytokines might play an important role. We have recently reported that chronic ITP patients in remission had elevated plasma levels of the Th3 cytokine transforming growth factor-beta1 (TGF-beta1), possibly as a part of a bystander immune suppression. In the present study we found that, in ITP patients with active disease [platelet count (plc) < 50 x 10(9)/l], mitogen-stimulated peripheral blood mononuclear cells (PBMC) had a significantly reduced production of TGF-beta1 (444 +/- 178 pg/ml; n = 6) compared with patients with plc 50-150 x 10(9)/l (1293 +/- 374 pg/ml; n = 9; P < 0.05), patients with plc >150 x 10(9)/l (1894 +/- 244 pg/ml; n =12; P <0.005) and healthy controls (1698 +/- 241 pg/ml; n = 10; P < 0.01). Nineteen per cent of ITP patients expressed a platelet-induced PBMC proliferation. Surprisingly, 22% of the ITP patients had a PBMC proliferation below the normal range, i.e. a suppressed proliferation in the presence of platelets; five of these six patients had active disease. In summary, this study demonstrated that chronic ITP patients with active disease had reduced PBMC production of the Th3 cytokine TGF-beta1. This result gives further support to the theory that chronic ITP in active phase is associated with a downregulated Th3-response.     

The Clinical Significance of Platelet-Associated IgG: a Study on 298 Patients with Various Disorders

S ummary . Platelet-associated IgG (PAIgG) was studied by a quantitative platelet radioactive anti-IgG test (PRAT) in 298 patients. At the time of investigation, 171 patients were thrombocytopenic (platelet count <100 × 10⁹/1), 127 had normal platelet counts. Patients fell into the following disease categories: Idiopathic thrombocytopenic purpura (ITP) ( N =81), possible ITP (19), acute ITP (9), systemic lupus erythematosus (22), autoimmune haemolytic anaemia of warm-type (18), systemic blood disease (65), liver diseases (35), others (49). A significant elevation of PAIgG was found in all disease categories. There was a significant correlation between PAIgG and the reciprocal values of platelet counts for most disease groups. No relationship was discernible between PAIgG and hypergammaglobulinaemic states (serum IgG >1.8 g/l), Platelet survival studies ( N=30 ) revealed that normal and increased values of PAIgG were associated with normal or shortened platelet mean life span. It is concluded that an elevated PAIgG is only one of several factors involved in the development of immunologically mediated thrombocytopenia.     

Detection of granulocyte-macrophage colony-stimulating factor in cerebrospinal fluid of patients with aseptic meningitis

The level of granulocyte-macrophage colony-stimulating factor (GM-CSF) in the cerebrospinal fluid from 14 infants and children with meningitis and 6 patients who suffered other diseases besides meningitis was measured by our sensitive enzyme linked immunosorbent assay for GM-CSF. The minimal detection level of GM-CSF was 40 pg/ml. Six of 9 patients (67%) with aseptic meningitis had detectable GM-CSF in cerebrospinal fluid and the concentrations of GM-CSF ranged from 49 to 114 pg/ml (mean 72 pg/ml), whereas none of 5 patients with bacterial meningitis or 6 patients with other diseases besides meningitis had detectable GM-CSF levels. There was no clear correlation between the GM-CSF levels in cerebrospinal fluid and the leukocyte count in either peripheral blood or cerebrospinal fluid, or the concentration of protein or glucose in cerebrospinal fluid.     

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.     

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.     

Measurement of platelet-associated IgG in animal models of immune and nonimmune thrombocytopenia

Platelet-associated IgG (PAIgG) is elevated in idiopathic thrombocytopenic purpura (ITP), but it also is elevated in other thrombocytopenic disorders traditionally considered to be nonimmune. Consequently it is possible that elevated PAIgG is a nonspecific finding secondary to thrombocytopenia. To study this issue we developed a rabbit model of immune and nonimmune mediated thrombocytopenia. The mechanism of the thrombocytopenia was validated by platelet survival studies. Immune thrombocytopenia was produced by injection of antirabbit platelet serum that was raised in guinea pigs. Nonimmune aregenerative thrombocytopenia was produced by irradiation of the animals; nonimmune consumptive thrombocytopenia was produced by injection of adenosine diphosphate (ADP). PAIgG was measured in a direct binding assay using 125I-labeled staphylococcal protein A (SpA). Washed platelets from normal, nonthrombocytopenic rabbits bound an average of 81 molecules of SpA per platelet (81 +/- 168, mean +/- 2 SD, n = 39). Infusion of the antiplatelet antiserum produced thrombocytopenia with a rise in PAIgG that was closely correlated with the level of PAIgG (r = 0.86, n = 12). The thrombocytopenia was consumptive, as shown by a very short platelet life span using 111In- labeled platelets. In contrast, both nonimmune thrombocytopenic states resulted in an equal or greater drop in the platelet count but no change in the level of PAIgG. The animals with aregenerative thrombocytopenia had normal or only moderately reduced platelet life spans; however, in every animal the level of PAIgG was not different from the nonthrombocytopenic controls, irrespective of the platelet count. Similarly, the level of PAIgG was unchanged in those rabbits with nonimmune consumptive thrombocytopenia following infusion of ADP (82 +/- 55 molecules of SpA per platelet, mean +/- SD, n = 6). These studies indicate that elevated PAIgG is a specific finding of immune thrombocytopenia and is not secondary to thrombocytopenia itself. Indirectly these results support our hypothesis that immune mechanisms contribute to more thrombocytopenic disorders than was once thought likely.     

A rapid quantitation of platelet-associated IgG by nephelometry

Platelet-associated IgG (PAIgG) was measured by a simple rapid nephelometric technique using washed solubilized platelets and commercially available, prestandardized reagents. Normal subjects with normal platelet counts had PAIgG levels of 2.1-6.7 fg/platelet. Subjects with idiopathic immune thrombocytopenic purpura (ITP) had levels of 7.2-43.3 fg/platelet. Ninety percent of ITP patients had values exceeding 2 SD units of the mean of normal subjects. Elevated values were also found in 17% of patients with recovered ITP, patients with SLE with and without thrombocytopenia, patients with thrombocytopenia occurring during septicemia, and patients with IGg myeloma. Results can be obtained within several hours of receipt of blood specimen, and are similar to the reports that used more complex techniques.