Detection of platelet-associated IgG in chronic immune thrombocytopenic purpura using antibody-coated polyacrylamide beads

Summary Platelet-associated IgG (PAIgG) was detected by means of anti-human IgG coated polyacrylamide beads (Immunobeads) technique in 32 patients with chronic ITP. Both a direct test (with in vivo sensitized platelets) and an indirect test (with in vitro loaded platelets) were carried out. The percent of rosette forming beads was both in the direct test (41.2%) and in the indirect test (32.6%) significantly higher in the cases of chronic ITP patients than in the controls (2.5% and 3.2%, respectively). These results confirm the diagnostic value of this new, relatively simple and rapid method in routine clinical practice.     

Relative importance of total versus external platelet-associated IgG

Summary We present measurements of total platelet-associated immunoglobulin G following platelet lysis (PAIgG tot) and surface-restricted IgG (PAIgG ext) on intact, gel-filtered platelets from 36 normal human donors and 9 patients with human immunodeficiency virus (HIV) infection (CDC stages IIb–IV). For this purpose, an indirect micro ELISA technique was developed involving competition between PAIgG and solid-phase absorbed IgG for fixation of conjugated anti-human IgG antibody. In normal donors, the mean values of PAIgG tot was 8.3±7.4 (mean ±2 SD) and of PAIgG ext 4.2±4.4 fg/platelet. In HIV-infected subjects, PAIgG tot was 37.2±62.8 and PAIgG ext 17.1±23 fg/platelet. In healthy subjects the comparison of individual levels of PAIgG tot and PAIgG ext revealed a significant correlation (r:0.763; p: 0.003). These results are compared to those which have been reported in the literature. In addition, the major immunopathological mechanisms considered responsible for immune-mediated idiopathic thrombocytopenic purpura are discussed.Presented at the International Workshop on ITP, August 26 and 27, 1988, Lucerne, Switzerland     

Severe thrombocytopenia suggesting immunological mechanisms in two cases of vivax malaria

Case 1: A 27-year-old woman, referred to our hospital because of relapsing fever after travel to Thailand, was given a diagnosis of vivax malaria. Clinical investigation revealed thrombocytopenia, elevated platelet-associated IgG (PAIgG), and negative antibody against Plasmodium vivax antigen. After antimalarial treatment, the levels of both the platelets and PAIgG returned to normal. Case 2: A 28-year-old Sri Lankan man was admitted to our hospital with a complaint of fever. The patient had thrombocytopenia, elevated PAIgG, and positive antibody against Plasmodium vivax antigen. He contracted malaria in Sri Lanka about 6 months prior to this admission. After treatment, the platelet count and PAIgG level returned to normal. In these two cases, high levels of PAIgG may have been involved in the development of the thrombocytopenia. In the first patient, in particular, the thrombocytopenia was thought to be induced by some immunological mechanism prior to the detection of antimaralial antibodies in serum. Am. J. Hematol. 56:183–186, 1997. © 1997 Wiley-Liss, Inc.     

Pattern of platelet-associated immunoglobulin (classes and IgG subclasses) in childhood immune thrombocytopenic purpura

Platelet-associated Ig classes and IgG subclasses were studied by a semiquantitative platelet ELISA test in 17 children with immune thrombocytopenic purpura (ITP). An elevation of PAIg was found in 94% of the children. In nearly all cases increased amounts of PAIgG of subclass G1 was seen, and in half of the cases increased amounts of PAIgM were also seen. No statistical difference in the composition of PAIg classes and PAIgG subclasses in acute and in chronic ITP was found. However, a correlation of increased amount of PAIgG3 and very low platelet count (20 x 10(9)/l) was observed.     

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.     

Platelet associated IgG, platelet mean life span and treatment with intravenous immunoglobulin in idiopathic thrombocytopenic purpura

The clinical significance of platelet associated IgG in ITP detected by direct platelet suspension immunofluorescence test (PSIFT) was studied. The platelet mean life span (MLS) was measured with 111In-labelled platelets in 17 adult patients. All the patients had shortened platelet MLS. The direct PSIFT was positive in 14 patients. Patients were initially treated with prednisone; 12 patients with poor response to the drug were splenectomised. 8 of these 12 patients were treated with intravenous immunoglobulin (IvIg) before splenectomy. The response to IvIg was as good or better in the 3 patients with negative PSIFT, than in the 5 patients with positive PSIFT.     

流式细胞术检测血小板相关IgG的临床应用

目的：研究流式细胞式（ＦＣＭ）检测血小板相关免疫球蛋白Ｇ（ＰＡＩｇＧ）的特点及在特发性血小板减少性紫癜（ＩＴＰ）诊断中的意义。方法：用ＦＣＭ检测了４７例ＩＴＰ、１３例非免疫性血小板减少、１０例自身免疫溶血性贫血、１８例其它免疫系统疾病患者以及３１例健康志愿者的ＰＡＩｇＧ,并与ＥＬＩＳＡ竞争法检测结果比较。结果：ＦＣＭ检测ＩＴＰ患者ＰＡＩｇＧ的平均荧光强度和阳性血小板百分率均明显高于正常对照组（Ｐ〈０．０１）,１１例有峰形异常。ＩＴＰ患者ＦＣＭ检测的阳性率（８７．２％）比ＥＬＩＳＡ法（８３．０％）稍高,两种方法的符合率为８５．１％。但两种方法都存在特异性不高的问题。结论：ＦＣＭ检测ＰＡＩｇＧ具有快速、简便和灵敏等特点,可作为免疫性血小板减少实验诊断的新方法。     

Intravenous gamma globulin decreases platelet-associated IgG and improves transfusion responses in platelet refractory states.

In an attempt to improve platelet transfusion responses, intravenous immunoglobulin (IV-IgG) was administered to 19 patients who were refractory to random and best available HLA-matched platelets. A response to IV-IgG was defined as two or more successive transfusions of HLA-matched products that provided recoveries greater than 30%. Thirteen of 19 (68%) patients responded to therapy at a median time of 7 days after initiation of IV-IgG (range = 2-17). Baseline platelet associated IgG levels (PalgG) were elevated in both the responders (61.6 +/- 76.2) (mean +/- SD) and the non-responders (47.0 +/- 46.3 fg/plt). Post-therapy, PalgG levels remained unchanged in the nonresponders but were decreased significantly (p = 0.05) to 11.1 +/- 6.2 fg/plt in the responders. The latter levels were similar to those (11.6 +/- 8.2 fg/plt) measured in a series of 36 transfusion responsive patients. This apparent decline in PalgG was not explained by differences in lymphocytotoxic antibodies (LCT-Ab) after therapy. Moreover, a high degree of alloimmunization was associated with a poorer response to IgG. Only two of eight patients with LCT panel-reactive antibody (PRA) of greater than 85% were responders. By contrast, improved transfusion outcomes were seen uniformly in patients with PRA greater than or equal to 85%. Improved recoveries were obtained using LCT-Ab compatible but not incompatible platelets. The median increment (% predicted) with compatible platelets before therapy was 6.0 +/- 9.9 (SD). Post-IgG, median recoveries were 37.0 +/- 31.2 percent, P less than 0.001. These findings suggest that IV-IgG may alter destructive mechanisms that affect the survival of compatible platelets in refractory patients.     

Pathophysiology and management of chronic immune thrombocytopenia: focusing on what matters

Immune thrombocytopenia (ITP) is a common autoimmune disease characterized by low platelet counts and an increased risk of bleeding. Antibody-mediated platelet destruction has been the prevailing hypothesis to explain ITP pathogenesis, supported by the efficacy of B-cell depletion therapy; however, the recent success of thrombopoietin receptor agonists lends support to the notion that platelet production is also insufficient. Best practice for the management of chronic ITP has not yet been established because data from comparative trials are lacking. Despite renewed interest in novel drugs capable of increasing platelet counts, ultimate treatment goals for ITP patients must be kept in mind: to improve patients' health and well-being. In this article, the pathophysiology of ITP is reviewed and key remaining questions about mechanism are explored. A rational approach to the management of ITP in adults is outlined, acknowledging evidence and evidence gaps, and highlighting the need for clinically important endpoints in future clinical trials.     

B cells and antibodies in refractory immune thrombocytopenia

Immune thrombocytopenia (ITP) is an acquired bleeding disorder mediated by pathogenic autoantibodies secreted by plasma cells (PCs) in many patients. In refractory ITP patients, the persistence of splenic and bone marrow autoreactive long-lived PCs (LLPCs) may explain primary failure of rituximab and splenectomy respectively. The reactivation of autoreactive memory B cells generating new autoreactive PCs contributes to relapses after initial response to rituximab. Emerging strategies targeting B cells and PCs aim to prevent the settlement of splenic LLPCs with the combination of anti-BAFF and rituximab, to deplete autoreactive PCs with anti-CD38 antibodies, and to induce deeper B-cell depletion in tissues with novel anti-CD20 monoclonal antibodies and anti-CD19 therapies. Alternative strategies, focused on controlling autoantibody mediated effects, have also been developed, including SYK and BTK inhibitors, complement inhibitors, FcRn blockers and inhibitors of platelet desialylation.     

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.     

Measurement of endogenous and exogenous alpha-granular platelet proteins in patients with immune and nonimmune thrombocytopenia

Idiopathic thrombocytopenic purpura (ITP) is caused by antiplatelet antibodies and is characterized by increased platelet destruction and elevated levels of IgG (platelet-associated IgG, PAIgG). Nonimmune thrombocytopenic patients also have elevated levels of PAIgG. In this study we investigated two possible biological explanations for the increased levels of PAIgG in these patients. The first hypothesis suggests that a thrombocytopenic stress causes increased thrombocytopoiesis with increased numbers and content of the platelet alpha granules. The second hypothesis is that for uncertain reasons (immunological or cytokine) there is increased absorption of plasma proteins by either megakaryocytes or by the platelets themselves. To address this issue, we compared the level of megakaryocyte synthesized alpha granular proteins [platelet factor 4 (PF4) and beta-thromboglobulin (beta-TG)] to plasma-absorbed alpha granular proteins (albumin, IgG and fibrinogen) in patients with immune (n = 39) and nonimmune (n = 60) thrombocytopenias. Plasma-absorbed alpha-granular proteins were elevated in both immune and nonimmune thrombocytopenia with no increase in megakaryocyte synthesized alpha-granular proteins. These plasma-derived protein elevations were not attributable to elevated mean platelet volumes or elevated plasma concentrations of the respective protein. We hypothesize that the increased IgG in these platelets is not the result of production of larger platelets, but reflects a selective increase in the endocytosis of plasma-absorbed alpha-granular proteins at the megakaryocyte and/or platelet level.     

Simultaneous measurements of megakaryocyte-associated IgG (MAIgG) and platelet-associated IgG (PAIgG) in chronic idiopathic thrombocytopenic purpura

Abstract: We have simultaneously measured platelet-associated IgG (PAIgG) and megakaryocyte-associated IgG (MAIgG) in 30 untreated patients with chronic idiopathic thrombocytopenic purpura (CITP). Megakaryocytes were purified from bone marrow by 35% Percoll gradient centrifugation, followed by negative immunopanning using magnetic immunobeads. The normal range of MAIgG in 30 healthy donors was 15.5 & 10.0 ng/10⁵ megakaryocytes, whereas MAIgG in the 30 CITP patients was 140 & 59.3 ng/10⁵ megakaryocytes, although the values were widely distributed. From the PAIgG and MAIgG data, CITP patients were classified into three types; type I (PAIgG < 200 ng/10⁷ platelets and MAIgG < 150 ng/10⁵ megakaryocytes), type II (PAIgG > 200 ng and MAIgG > 150 ng), and type III (PAIgG < 200 ng and MAIgG > 150 ng). Patients with types I and III had good clinical courses, but, in contrast, patients with type II responded poorly to steroid therapy followed by splenectomy or became refractory to treatment. In splenectomized patients, MAIgG of responder was promptly decreased to normal range and, in contrast, that of non-responder was persistently elevated. These results indicate that anti-platelet autoantibodies are able to bind with megakaryocytes in the bone marrow as well as with platelets in the peripheral blood, and the results also suggest that megakaryopoiesis in CITP is heterogeneous. Simultaneous measurement of PAIgG and MAIgG may predict the clinical outcome of CIPT.     

The IgG subclasses of platelet-associated autoantibodies directed against platelet glycoproteins IIb/IIIa in patients with idiopathic thrombocytopenic purpura

The majority of patients with idiopathic thrombocytopenic purpura (ITP) have antiplatelet autoantibodies that are most frequently directed against platelet glycoproteins IIb/IIIa or Ib/IX/V. However, there is some debate whether the immune response is oligoclonal or polyclonal in nature. We investigated the subclass distribution of anti-IIb/IIIa IgG autoantibodies in 59 prospectively studied patients with ITP. We also tested patients with a variety of thrombocytopenic disorders (n=31) and healthy controls (n=30). Platelet lysates were tested for IgG anti-IIb/IIIa autoantibodies, and the specific IgG subclass distribution was measured using antigen capture assays. All testing was done blinded to diagnosis and other assay results. After unblinding, we found that 43 of the 59 ITP patients had anti-IIb/IIIa autoantibodies (sensitivity=73%). Anti-IIb/IIIa autoantibodies were also detected in five of the 31 non-ITP patients, but in none of the 30 healthy controls (specificity=91%). The IgG subclass assay was positive in 39 of the 43 ITP patients with anti-IIb/IIIa antibodies (sensitivity=92%) and in 12 samples that had no detectable anti-IIb/IIIa antibodies including two ITP patients (specificity=83%). The most common subclass in the ITP patient samples was IgG1 (77%), either alone (n=14) or with other IgG subclass antibodies (n=19). However, there were also patients with only IgG2 (n=2), IgG3 (n=3) or IgG4 (n=3) antibodies. Our results are consistent with the hypothesis that ITP is a heterogeneous disorder and that some patients have evidence of oligoclonality, whereas other patients have polyclonal autoantibodies.     

Comparison of two direct assays for platelet-associated IgG (PAIgG) in assessement of immune and nonimmune thrombocytopenia

A number of methods have been developed to measure platelet-associated IgG (PAIgG). The antiglobulin consumption assay directly quantitates IgG on the platelet and is sensitive and specific. A fluorescent anti- IgG assay has recently been described and has the advantage of simplicity. We compared the results of these two PAIgG assays in immune and nonimmune thrombocytopenia and nonthrombocytopenic controls. The antiglobulin consumption assay was negative in 61 of 62 and the fluorescent negative in 54 of 62 assays in nonthrombocytopenic controls, and they were negative in 11 of 13 and 8 of 13 assays, respectively, in nonimmune thrombocytopenic patients. The antiglobulin consumption assay was positive in 54 of 58 and the fluorescent positive in 24 of 58 assays of patients with immune thrombocytopenia (ITP and SLE). The overall sensitivity and specificity of the antiglobulin consumption assay was 94% and 95% and of the fluorescent assay was 44% and 82%.     

Role of elevated platelet-associated immunoglobulin G and hypersplenism in thrombocytopenia of chronic liver diseases

BACKGROUND AND AIM: Thrombocytopenia typically worsens with the progression of liver disease and can become a major clinical complication. Several mechanisms that contribute to thrombocytopenia have been proposed, including hypersplenism accompanied by increased platelet sequestration, platelet destruction mediated by platelet-associated immunoglobulins (PAIgG), and diminished platelet production stimulated by thrombopoietin (TPO). The purpose of the present study was to evaluate the role of each of these mechanisms in patients with liver disease-associated thrombocytopenia. METHODS: Twenty-nine patients with liver cirrhosis (LC), 20 of whom were hepatitis C virus (HCV)-seropositive, 29 chronic hepatitis (CH) patients, 24 of whom were HCV-seropositive, and 16 control patients without liver or hematopoetic disease were enrolled in this study. Serum TPO levels, PAIgG, and liver-spleen volumes were determined and correlation analyses were performed. RESULTS: No differences in serum TPO levels were observed among the three groups. The PAIgG levels were significantly elevated in CH and LC patients (mean +/- SD: 56.5 +/- 42.3 and 144.6 +/- 113.6 ng/107 cells, respectively) compared with the controls (18.9 +/- 2.5 ng/107 cells, P < 0.001 for both). Spleen volume was significantly higher only in LC (428 +/- 239) compared with CH (141 +/- 55) and control (104 +/- 50 cm3) (P < 0.001), while liver volume was not significantly different between the three groups. Correlation analyses demonstrated a significant negative correlation between platelet count with PAIgG (r = - 0.517, P < 0.001) and spleen volume (r = - 0.531, P < 0.001), and no relationship between platelet count and serum TPO level (r = 0.076). CONCLUSIONS: Serum TPO level may not be directly associated with thrombocytopenia in patients with chronic hepatitis and liver cirrhosis. In contrast, spleen volume and PAIgG are associated with thrombocytopenia in such patients, suggesting that hypersplenism and immune-mediated processes are predominant thrombocytopenic mechanisms.     

High-dose intravenous IgG in the management of pregnancy in women with idiopathic thrombocytopenic purpura

Idiopathic thrombocytopenic purpura (ITP) may develop during pregnancy or affect later pregnancies, causing serious risks of bleeding to the mother and fetus. High-dose intravenous immunoglobulin (IGIV) has caused an immediate and predictable rise in platelet count during the infusion in both adults and children with chronic or acute ITP. The rapid rise in platelet counts may be important in preparing pregnant women with ITP for surgery or delivery. We report our experience in managing two women at weeks 29 and 37 week of gestation who required splenectomy and/or cesarean section. Both patients demonstrated an increase in platelet counts, underwent surgery without excess bleeding, and had normal infants with normal platelets, and with mild thrombocytopenia at delivery.     

Beyond the platelet count: immature platelet fraction and thromboelastometry correlate with bleeding in patients with immune thrombocytopenia

Platelet counts (PC) estimate bleeding risk in Immune Thrombocytopenia (ITP). We investigated whether measures of thromboelastometry and absolute immature platelet fraction (A‐IPF) would correlate better with acute bleeding score (ABS) than PC or mean platelet volume (MPV). Simultaneous determination of ABS, complete blood count and thromboelastometry was performed in 141 ITP patients; 112 underwent A‐IPF testing. Subgroup analyses were performed for paediatric subjects, PC <60 × 10⁹/l and <30 × 10⁹/l. PC significantly inversely correlated with ABS in all subjects, PC <30 × 10⁹/l and total paediatric cohort. MPV did not correlate with ABS in any subgroup. Thromboelastometry measures of clot firmness, but not PC, significantly correlated with ABS in all subjects with PC <60 × 10⁹/l, and children with PC <60 × 10⁹/l and <30 × 10⁹/l. A‐IPF demonstrated stronger correlation with ABS than did PC among all subjects, those with PC <60 × 10⁹/l, all children and children with PC <30 × 10⁹/l (r = ?0·37; r = ?0·34; r = ?0·44; r = ?0·60) versus ABS with PC (r = ?0·36; ns; r = ?0·32; ns). Stronger correlations of both thromboelastometry measures of clot firmness and A‐IPF than PC with ABS suggest factors beyond PC, i.e. related to platelet function, contribute to ITP bleeding pathophysiology. Thromboelastometry, A‐IPF and ABS can be incorporated into routine or acute visits.     

Glycocalicin in the diagnosis and management of immune thrombocytopenia

Abstract: We studied glycocalicin (GC), expressed as plasma GC concentration and as GC index (ratio to platelet count), in 129 thrombocytopenic patients (platelet count <100×10⁹/1) and 60 sex- and age-matched controls. Seventy-two patients had idiopathic immune thrombocytopenia, 32 secondary immune thrombocytopenia, 8 microangiopathic thrombocytopenia and 17 thrombocytopenia secondary to bone marrow aplasia. Patients with immune thrombocytopenia (ITP) were also subclassified, according to their clinical behaviour, as having active disease or being in spontaneous or therapy-induced partial remission. A significant correlation was found between glycocalicin levels and platelet count both in normals and in patients with bone marrow aplasia (r = 0.75). ITP patients showed a GC index significantly higher than controls (6.02±7.87 vs. 0.9±0.2, p<0.001). When ITP patients with similar platelet count (30–50×10⁹/l) were studied, the mean level of GC and the GC index were significantly higher in those patients with active disease than in those in remission (0.97±0.38 vs. 0.58±0.17 μg/ml, p<0.05; 6.41±2.64 vs. 3.44±0.94, p<0.05, respectively). A longitudinal study performed in 10 patients with different subtypes of ITP suggested a positive correlation between GC index and the activity of the disease. The GC value and GC index were significantly higher in patients with microangiopathic thrombocytopenia than in controls (1.44±0.73 vs. 0.8±0.16 μg/ml, p<0.01; and 18.77±22.23 vs. 0.9±0.2, p<0.001, respectively). The GC value was significantly lower in bone marrow failure (0.15±0.04 μg/ml, p<0.01) compared to controls, while no difference was observed in the GC index. Our data confirm that the GC index is helpful in differentiating thrombocytopenia due to increased platelet destruction from the one due to impaired production. In addition, the assay has been proven useful in the differential diagnosis of different ITP subtypes and their follow-up.     

Multirefractory primary immune thrombocytopenia; targeting the decreased sialic acid content

Patients with multirefractory immune thrombocytopenia (ITP) have limited treatment options. Recent data suggest that specific anti-platelet antibodies may cause destruction of platelets by favoring platelet loss of sialic acid. In this multicenter study 35 patients with ITP, including 16 with multirefractory disease, were analyzed for antiplatelet-antibodies, thrombopoietin (TPO) levels, and platelet desialylation. In selected cases, responses to a novel treatment strategy using oseltamivir were tested.

We found that antibodies against GPIbα were overrepresented in multirefractory patients compared to responders (n = 19). In contrast to conventional ITP patients, multirefractory patients exhibited a significant increased platelet activation state (granule secretion) and desialylation (RCA-1 binding) (p < 0.05), and a trend toward higher plasma TPO concentrations. The decreased sialic acid content seemed to be restricted to platelet glycoproteins, since other plasma proteins were not hypoglycosylated. A total of 10 patients with multirefractory ITP having remarkable loss of platelet terminal sialic acids were given oseltamivir phosphate. When the antiviral drug was combined with TPO receptor agonists (TPO-RAs) or with immunosuppressant drugs, platelet responses were observed in 66.7% of patients. All responding patients presented with antibodies reactive only against GPIbα.

These findings suggest that desialylation may play a key pathogenic role in some multirefractory ITP patients, and provide diagnostic tools for the identification of such patients. Furthermore, we show that sialidase inhibitor treatment in combination with therapies that help to increase platelet production can induce sustained platelet responses in some patients with anti-GPIbα -mediated thrombocytopenia that have failed previous therapies.