Platelet associated IgG, platelet survival, and platelet sequestration in thrombocytopenic states

Platelet hyperactivation in multiple myeloma is also evident in patients with premalignant monoclonal gammopathy of undetermined significance

Thrombotic events are common in patients with multiple myeloma (MM), smouldering myeloma (SM) and monoclonal gammopathy of undetermined significance (MGUS). Previous studies have indicated platelet hyperactivation as a feature of thrombotic risk in MM, but there is a dearth of data in MGUS. In the present study, multiparameter analysis of platelet activation and responsiveness was investigated by flow cytometry in patients with MGUS, SM/MM and healthy controls (HCs). The median platelet surface CD63 levels, annexin V and PAC-1 antibody (specific for activated integrin αIIbβ3) binding were significantly elevated in patients with MGUS versus the HCs. These markers were also elevated in SM/MM, but not significantly. In all, 74% of MGUS and 38% of SM/MM patients had one or more elevated marker of platelet activation, compared to 19% of the HCs. Marker-specific hyporesponsiveness of platelets to agonist [adenosine diphosphate (ADP), thrombin receptor-activating peptide 6] stimulation in vitro was observed, with significantly reduced surface levels of P-selectin in response to ADP in patients with MGUS. Platelet-leucocyte aggregates were not altered in patients, while platelet-associated immunoglobulins were elevated in a subset of patients. Overall, we found that platelet hyperactivation is prevalent in both MGUS and SM/MM patients and is potentially related to hyporesponsiveness. These observations suggest that further investigation of the predictive and prognostic value of platelet hyperactivation in such patients is warranted.

Detection of various platelet-associated immunoglobulins by flow cytometry in idiopathic thrombocytopenic purpura

BACKGROUND

In 1975, Dixson reported that anti-platelet IgG on platelets from patients with idiopathic thrombocytopenic purpura (ITP) is greater than in normal people, by determining anti-platelet antibodies directly on the platelet surface with a quantitative complement lysis-inhibition-assay. Since then, platelet-associated IgG (PAIgG) has been thought of as evidence of ITP. Although platelets from ITP patients show significantly higher PAIgG values than from normal control individuals, PAIgG is not specific for autoantibody because it increases in other than immune ITP patients.

METHODS

We analyzed positive platelet percentage with various platelet-associated immunoglobulins: IgG, IgM, IgA, and total immunoglobulins, in the blood from 17 normal donors and 23 ITP patients.

RESULTS

The specificity for ITP disease was better in flow cytometry than in ELISA, because, other than ITP, only aplastic anemia was positive in flow cytometry; however, various disorders (aplastic anemia, chronic lymphocytic leukemia, acute myeloid leukemia, and myelodysplastic syndrome) showed positive in ELISA. Flow cytometry methods had the same sensitivity for ITP disease as ELISA. However, it is supposed that there was no nonimmune ITP in this study because the PAIgG negative patients (n = 1) showed positive results in flow cytometry.

CONCLUSION

Flow cytometry method was effective for ITP screening, especially for specificity.

The etiology of childhood immune thrombocytopenic purpura: how complex is it?

Recent developments in genomics and basic immunology have provided a new set of tools for investigation into the etiology and treatment of childhood immune thrombocytopenia purpura (ITP). The genomic revolution is generating a catalog of germ-line common genetic variants, some of which could influence the susceptibility or outcome of ITP. Similarly, in vitro analyses and animal models have been employed to probe the basic alterations underlying ITP. The emergence of a more refined understanding of complex diseases such as ITP has important implications for prevention, therapy, and follow-up. The relative contribution of the genetic component and its interaction with the strong environmental stimulus, such as an acute, antecedent viral infection, remains to be determined.

Prophylactic platelet transfusions: which dose is the best dose? A review of the literature

Routine platelet transfusions for patients with acute leukemia were introduced in the early 1960s, and since then platelet use has increased steadily. Despite widespread use, good clinical evidence supporting prophylactic platelet transfusions is limited, and there are very few studies that have examined the dose for prophylactic platelet transfusions. Review of the platelet dose used in both early studies of routine platelet transfusions and more recent clinical trials of platelet transfusions shows wide variation in dosing, which is also reflected in clinical practice. As such, only limited recommendations for platelet dose have been forthcoming from consensus conferences or guidelines. The results from 3 recent clinical trials and a mathematical model examining the dose for prophylactic platelet transfusions suggest that lower dose transfusions may decrease the total number of platelets transfused; however, no definitive conclusions about the optimal platelet dose can be reached as these trials were not designed to evaluate bleeding outcomes or total platelet utilization. Future large clinical trials of platelet dose, which examine these critical outcomes, are required. Only with these results can the optimal platelet dose be determined.

Immune thrombocytopenic purpura

Although many advances have been achieved in the understanding of ITP, critical issues regarding the pathophysiology and biology of the disease remain to be elucidated. The recent characterization of the human genome along with new sophisticated molecular biology techniques will allow basic researchers to study genes that may affect the presentation and clinical course of the disease. Different patterns of gene expression in this population can be studied, leading to the identification of subsets of patients with ITP at higher risk of bleeding. The multigene patterns of expression might also provide clues about regulatory mechanisms and broader cellular functions. In order to answer essential clinical questions, like the incidence of ICH in relation to drug treatment or observation alone, clinical trials should be appropriately designed. More studies are necessary to better define the optimal treatment approach for each child with ITP. Even though the incidence of intracranial hemorrhage cannot be used as the primary outcome measure because of its rarity, numerous other outcomes, such as rate of rise in platelet count, cost and side effects of therapy, health related quality of life of the patient and family, and severity of hemorrhage can be measured and compared between treatment groups. Future investigators should find it attractive to conduct trials in children with this common hematological disease so that decision making can be based more on scientific evidence than on anecdote and opinion.

Immune thrombocytopenic purpura in patients with chronic hepatitis C virus infection

OBJECTIVE

Hepatitis C virus (HCV) infection has been associated with the production of autoantibodies and the development of several autoimmune disorders. Immune thrombocytopenic purpura (ITP) is an immune-mediated syndrome of unknown etiology characterized by the presence of autoantibodies against platelet membrane proteins.

METHODS

Retrospective chart review.

RESULTS

Seven patients with chronic HCV infection (five with cirrhosis and two with chronic active hepatitis) developed thrombocytopenia, out of proportion to their liver disease, and were diagnosed with ITP based on the presence of anti-platelet antibodies and their response to treatment. The number of patients with ITP which occurred in a population of 3440 HCV patients seen over this time interval is much greater than would be expected by chance (p < 0.00001). Six patients required treatment and four required hospitalization. Four of the six responded to corticosteroids alone. Both of the patients who failed to respond to corticosteroids responded to cyclophosphamide. No mortality occurred from complications of thrombocytopenia.

CONCLUSIONS

ITP occurs more commonly in patients with chronic HCV infection than would be expected by chance. This should be considered in patients with liver disease and unexplained thrombocytopenia, as well as in patients with newly diagnosed ITP. Evaluation of antiplatelet antibodies, using an antigen-specific assay, was useful in supporting this diagnosis. Therapy with either corticosteroids or cyclophosphamide was successful in the six patients who required treatment.

Pathophysiology of immune thrombocytopenic purpura

In 1951, the young hematologist in training, Dr. William Harrington, infused himself with plasma from a patient with immune thrombocytopenic purpura (ITP). He rapidly developed severe, but transient, thrombocytopenia and was at risk for serious hemorrhage. Thus, the humoral autoimmune cause of ITP was established. Since 1953, when Dr. Harrington's in vivo studies ended, in vitro investigations have aimed to determine the molecular and cellular details of immune-mediated platelet destruction.

Advances in the diagnosis of idiopathic thrombocytopenic purpura

Idiopathic thrombocytopenic purpura (ITP) remains a clinical diagnosis made by the exclusion of other causes of thrombocytopenia. It is based on the patient's history, physical examination, and complete blood cell count, as well as examination of the blood film. Over the last four decades, a number of platelet antibody tests have been developed to aid the diagnosis of ITP. They can be divided chronologically into three groups. Phase I assays measure a functional change in control platelets after incubation with test serum. Because their sensitivity and specificity are low, they are no longer used to diagnose ITP. Phase II assays measure platelet-associated IgG by three different approaches. They lack the ability to differentiate between pathologic and nonpathologic platelet-associated IgGs. These assays are sensitive (80% to 90%) but their specificity is too low for them to be diagnostically useful. Phase III assays are the latest development in platelet serology testing. They measure glycoprotein-specific platelet antibodies by different approaches, namely, immunoblot, immunoprecipitation, and glycoprotein immobilization. Despite their high specificity, they suffer from low sensitivity (47% to 60%), which must be improved if they are to be clinically useful for the diagnosis of ITP.

Autoantibodies and autoantigens in chronic immune thrombocytopenic purpura

Chronic immune thrombocytopenic purpura (ITP) is an autoimmune disorder in which antiplatelet autoantibodies bind to antigens on the surface of platelets, resulting in their destruction. The newer antigen-specific (phase III) assays can detect platelet-associated and plasma autoantibodies in approximately 75% and 50% of patients, respectively. Antiplatelet autoantibodies bind to both platelets and megakaryocytes and preliminary evidence suggests that they not only cause platelet destruction but can also decrease platelet production either by interfering with megakaryocyte proliferation/maturation or by causing intramedullary platelet destruction. Autoantibodies are capable of activating complement and causing platelet phagocytosis both in vitro and in vivo. Many platelet-associated and plasma autoantibodies from ITP patients are light chain-restricted, which suggests a clonal origin. Approximately 75% of platelet autoantigens are localized to either the platelet glycoprotein (GP) IIb/IIIa or Ib/IX complex. Inhibition of the binding of autoantibodies from several ITP patients by either another ITP autoantibody or by a monoclonal anti-GPIIb/IIIa antibody suggests that the antigenic repertoire in chronic ITP may be limited. Most autoantigens on GPIIb/IIIa appear to be conformational since they are dependent on the presence of divalent cations. A variety of new investigative techniques have localized a few autoantigens to specific regions of the cytoplasmic or extracellular regions of both GPIIb/IIIa and GPIb/IX.

Influence of Monoclonal Antiplatelet Glycoprotein Antibodies on In Vitro Human Megakaryocyte Colony Formation and Proplatelet Formation

The influence of antiplatelet glycoprotein (GP) antibodies on megakaryocytopoiesis in patients with idiopathic or immune thrombocytopenic purpura (ITP) has been well studied. However, the influence of GP antibodies on proplatelet formation is poorly understood. Here we investigated whether in vitro human megakaryocyte colony formation and proplatelet formation are affected by various monoclonal antiplatelet GP antibodies (MoAb). The megakaryocyte colony formation inhibition assay was performed by methylcellulose culture with modifications, using peripheral blood nonadherent mononuclear cells. The proplatelet formation inhibition assay was performed by megakaryocytes derived from CD34+ cells, stimulated with thrombopoietin + stem cell factor, which were then incubated with antiplatelet GP MoAb for 24 or 48 hours. Anti-GP-Ib MoAb (CD42b; HIP1) slightly inhibited megakaryocyte colony formation (P &lt; .05). and strongly inhibited proplatelet formation (after 24 hours incubation, P &lt; .0002; after 48 hours incubation, P &lt; .0007). Anti-GP-IIb MoAb (CD41; 5B12) inhibited only proplatelet formation (only after 24 hours incubation,P &lt; . 03). Anti-integrin vβ3MoAb (CD51/CD61; 23C6) only slightly inhibited colony size (P &lt; .05). However, anti-GP-IIIa MoAb (CD61; Y2/51) did not inhibit either colony formation or proplatelet formation. These results suggest that antiplatelet GP MoAbs have differing effects on in vitro megakaryocyte colony formation and proplatelet formation.

Abdominal SPECT/MRI fusion applied to the study of splenic and hepatic uptake of radiolabeled thrombocytes and colloids

The importance of applying MRI (CT)/SPECT fusion in the abdominal and thoracic areas has been recognized in recent studies aiming at radionuclide therapy of cancer. According to our earlier results spleen and liver volume determination with different segmentation methods is inaccurate with SPECT alone. We therefore applied a SPECT/MRI registration procedure to the estimation of spleen and liver volumes and spleen/liver activity ratios in three male volunteers administered 111In-labeled thrombocytes and 99mTc-labeled colloids. The objectives of the study were to investigate if the uptake of thrombocytes in the spleen and liver can be measured more accurately when the anatomical borders of these organs are transferred from MRI to SPECT, and to test a SPECT/MRI registration method for improving three-dimensional dosimetry for radiotherapy treatment planning. A good correlation was found between spleen/liver activity ratios calculated from volumetric average activity per pixel values and from total volumetric counts derived from registered data but not from projection data. The average registration residual with this SPECT/MRI fusion method is approximately 1-2 cm in the abdominal area. Combining anatomical images with SPECT is therefore important for improving quantitative SPECT also in the abdomen.

Platelet autoantibodies in patients with chronic liver disease

The thrombocytopenia in chronic liver disease (CLD) has been attributed mainly to hypersplenism, although other factors such as reduced mean life span with increased platelet turnover have also been demonstrated. Immunological abnormalities have been described in the pathogenesis and progression of CLD. In this sense, many studies have reported elevated levels of platelet associated IgG (PAIgG) in patients with CLD, and it has been suggested that PAIgG could represent true antiplatelet antibody. In this study we used a glycoprotein (GP)-specific immunoassay (MACE) to determine whether PAIgG or circulating antiplatelet antibodies, reacted against the GPIIb/IIIa or GPIb/IX complexes, in patients with CLD. Thirty-six patients with CLD of diverse etiology were studied (20 female, mean age 53 years, range 38-75 years). 23 out of 36 patients (64%) had anti-GP antibodies in MACE. Particularly, 12 had anti-GPIb, 4 anti-GPIIb/IIIa, and 7 had both types of autoantibodies. The existence of these anti-GP antibodies was not related with the blood platelet count or etiology of CLD. These data show that in patients with CLD of diverse origin, there is a high prevalence of autoantibodies reacting specifically with platelet membrane GP, which constitutes the first evidence of the specific nature of platelet-bound IgG in CLD. These findings suggest that in patients with CLD, an immune mechanism may participate in inducing or aggravating the thrombocytopenia.

Study of platelet-associated immunoglobulins of IgG, IgM, IgA, and IgE classes and platelet kinetics in 33 patients with idiopathic thrombocytopenic purpura

The role of platelet-associated immunoglobulins (PAIg) of four different immunoglobulin classes--IgM, IgG, IgA, and IgE--and their relation to platelet count and platelet kinetics was studied in 33 patients with idiopathic thrombocytopenic purpura (ITP). During the course of 1 year, repeated determinations of PAIg were made. The results indicate that PAIgG, PAIgM, and PAIgA are present in all ITP patients, and that autoantibodies of all three Ig classes show highly significant correlations to the platelet counts (p < 0.0001). Double logarithmic negative correlations have been found between PAIgG and platelet count (r = -0.71), PAIgM and platelet count (r = -0.84), and PAIgA and platelet count (r = -0.79). Statistical analyses using partial correlation and multiple regression methods showed that PAIgM is predominantly related to the platelet count, whereas PAIgG and PAIgA are only of secondary importance. Accordingly, a relation of PAIgM (and PAIgA) to increased liver destruction of platelets was found in kinetic studies using 111indium-labeled platelets. Taken together, these results suggest a predominant role of PAIgM in the pathogenesis of ITP.

The site of platelet destruction in thrombocytopenic purpura as a predictive index of the efficacy of splenectomy

The significance of the site of platelet sequestration in determining the indication for splenectomy in idiopathic thrombocytopenic purpura (ITP) is a controversial subject. However, most of the negative conclusions are based on 51chromium labelling of homologous platelets. We report here the results of an analysis of 222 cases in which the kinetic study of 111indium-oxinate-labelled autologous platelets was performed under homogeneous technical conditions. 103 of these patients subsequently underwent splenectomy. This study demonstrates that the site of platelet sequestration in active ITP constitutes a variable independent of the patient's age, history of the disease and its severity (platelet count, lifespan). The sequestration site is a good predictive element of the short-term efficacy of splenectomy (71/76 cases with splenic sequestration obtained a platelet count exceeding 100 x 10(9)/l versus 7/13 cases with mixed sequestration and 1/14 cases with hepatic sequestration), and the long-term results (6 months to 5 years after splenectomy) do confirm the clinical value of this study.

Effect of recombinant interferon-alpha2C on reticuloendothelial function in patients with thrombocytosis

The aim of the study was to investigate the influence of recombinant interferon-alpha 2C (rIFN-alpha 2C) on the in vivo Fc-dependent phagocytic activity of the reticuloendothelial (RE) system. Fourteen patients with excessive thrombocytosis due to myeloproliferative disorders were studied before and 3 months after initiation of therapy. RE function was determined by measuring the clearance of autologous red blood cells (RBC) labeled with 51Cr and sensitized with anti-D antibody. Eleven of the 14 patients responded to rIFN-alpha 2 treatment (platelets, less than 440 X 10(9)/liter). Rather in contrast to a shortening of platelet half-life and an increase (trendwise) in platelet-bound IgG, rIFN-alpha 2 caused a significant impairment of RE function. Although this finding could in part be accounted for by the treatment-related decrease in splenic volume, statistical analysis revealed a direct influence of rIFN-alpha 2 on RBC clearance (p less than 0.01). Our study results might be explained by an interferon (IFN)-induced, intensified expression of Fc receptors on platelet (and leukocyte) surfaces, possibly enhancing unspecific binding of IgG to their cellular membranes. The subsequent increased platelet uptake may lead to an overloading of the RE system causing impaired reactions to additional stimuli such as IgG-coated RBC.

Clinical value of a direct platelet suspension immunofluorescence test in adult idiopathic thrombocytopenic purpura

109 adult patients with ITP were tested with the direct platelet suspension immunofluorescence test (PSIFT) for platelet-associated immunoglobulins (PAIg). 88 patients (81%) had a positive direct PSIFT. The mean platelet level at the time of the test was 45.2 X 10(9)/l [corrected] (SD = 28.8) with no difference between PSIFT-positive and -negative groups. The results of direct PSIFT were of limited value in predicting patient outcome. The overall better prognosis of patients with a negative direct PSIFT compared to those with a positive result was statistically significant. The PSIFT negatives achieved complete remission more often than PSIFT positives; and they also showed a tendency for a better response to splenectomy and therapy with high-dose i.v.Ig. Moreover, all the 21 patients refractory to therapy with corticosteroids, splenectomy or i.v.Ig, were PAIg positives.

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.

Intravenous immunoglobulin (i.v. IgG) for previously treated acute or for chronic idiopathic thrombocytopenic purpura (ITP) in childhood: a prospective multicenter study

In a prospective multicenter study 42 thrombocytopenic (less than 30 X 10(9) platelets/l) children with chronic idiopathic thrombocytopenic purpura (ITP) or with acute ITP, dependent on or refractory to corticosteroids, were given 0.4 g i.v. IgG/kg body weight/day on 5 consecutive days and thereafter once a week if the platelet count fell to less than 20 X 10(9)/l or if the patient bled. After the initial 5 days of i.v. IgG the platelets rose within a mean of 7-8 days to greater than 30 X 10(9)/l in all and to greater than 150 X 10(9)/l in 33 of 42 patients (79%). After a mean observation time of 26.6 months 26 of 42 patients (62%) showed a satisfactory long-term effect, i.e. no need for treatment for at least 6 months without bleeding and with no platelet counts below 20 X 10(9)/l. No difference in response rate was found between children with chronic and those with previously treated acute ITP. These results indicate that i.v. IgG could be used to control emergency situations, e.g. to stop bleeding or to prepare a patient for surgery. I.v. IgG also represents a good alternative to treatment modalities, such as splenectomy and/or the administration of cytostatic immunosuppressants with potentially serious side effects. In addition to the expected transient rise in serum IgG levels, i.v. IgG induced a more prolonged elevation of serum IgM. Platelet associated IgG, elevated before therapy, was correlated with the clinical long-term outcome.

Competitive enzyme-linked immunoassay for the quantitation of platelet-associated immunoglobulins (IgG, IgM, IgA) and complement (C3c, C3d) with polyclonal and monoclonal reagents

A competitive enzyme-linked immunoassay (CELIA) was developed for the quantitation of platelet-associated immunoglobulins and complement proteins. The use of unlabeled polyclonal rabbit or monoclonal antibodies to human immunoglobulins and enzyme-labeled anti-mouse or anti--rabbit IgG (double-step technique) resulted in a higher sensitivity compared to the single-step technique using only enzyme-labeled anti-human immunoglobulin antibody preparations. Sensitivity and results obtained by both techniques were compared. The range of normal values for platelet-associated IgG, IgM, IgA, C3c and C3d was assessed upon a large number of normal blood donors. When platelet-associated IgG was concomitantly assayed with polyclonal and monoclonal anti-IgG by the double-step technique on platelets obtained from normal donors and thrombocytopenic patients, identical results were obtained with both reagents. Problems related to the quantitation of immunoglobulins on platelets with different assays and antibody preparations are discussed.

Effect of danazol in immune thrombocytopenic purpura

Danazol and vinblastine are effective in many patients with chronic immune thrombocytopenic purpura (ITP). To evaluate the mechanism of action of these drugs, we studied six consecutive patients with chronic ITP treated with danazol and one treated with vinblastine. All the patients responded clinically without a notable change in the level of platelet-associated IgG. Instead, the clinical response to therapy was associated with a decrease in the number of monocyte binding sites for monomeric IgG (Fc receptors). In one patient, clinical relapse was associated with a spontaneous 2.7-fold increase in the number of monocyte Fc (IgG) receptors, without a change in the level of platelet-associated immunoglobulin. A decrease in the number of monocyte Fc (IgG) receptors following vinblastine infusion was associated with a clinical remission. We conclude that the clinical course of ITP may be influenced by the expression of monocyte or macrophage Fc (IgG) receptors. Danazol and vinblastine may mediate their clinical effect, at least in part, by influencing the number of available Fc (IgG) receptors on phagocytic cells.

[Detection of platelet antibodies in idiopathic thrombopenic purpura]

The authors report the results of Dixon's assay modified by Follea in 24 cases of idiopathic thrombocytopenic purpura. The level of immunoglobulin G bound to platelet membrane was increased in 91 p. 100 of patients in the acute phase of the disease. An inverse correlation was demonstrated between platelet-bound antibody levels and platelet count as well as platelet survival. In all cases of refractory idiopathic thrombocytopenic purpura, the assay was positive and the mean level was higher. When the platelet count improved after prednisone therapy or after splenectomy, the level decreased. Platelet antibody determination seems to be useful for predicting the course of the disease. Patients with normal immunoglobulin G bound to platelet might have only C3, IgM or IgA. Dixon's assay is not specific to idiopathic thrombopenic purpura, since it is positive in other types of thrombocytopenia, but immunoglobulin G bound to platelet probably represents specific antiplatelet antibodies.

Clinical significance of positive platelet immunofluorescence test in thrombocytopenia

The sensitivity and specificity of the platelet immunofluorescence test for the diagnosis of idiopathic thrombocytopenia (ITP) was studied in a series of 255 patients. Patients' platelets were tested directly. Diethyl-ether eluates of these platelets and patients' sera were tested indirectly with normal donor platelets. When all three tests were considered, positive results were obtained for 92.0% of the ITP patients with a platelet count of less than 150 X 10(9)/l and for 98.4% of the patients with a count of less than 100 X 10(9)/l. However, for many patients rather weak test results were obtained, with a score of 1/2-1 in 59.8% of the patients. Most patients (94.1%) with a positive direct test had a positive indirect test on the eluate. Thus, platelet-bound antibodies but not platelet-bound immune complexes were present in most, if not all, patients. Positive immunofluorescence tests were obtained for many patients with a diagnosis other than ITP. This resulted in a low specificity of the test for the diagnosis of ITP, evidently because autoimmune thrombocytopenia occurred together with many other diseases and also because antibodies against platelet cryptantigens (expressed by the action of EDTA or by platelet fixation) were present in many patients.

Platelet-associated immunoglobulins IgG, IgM, IgA and complement C3 in immune and nonimmune thrombocytopenic disorders

A two-stage radioactive antiglobulin test--using unlabelled antisera specific for IgG, IgA, IgM and C3 followed by binding of 125I-staphylococcal protein A--was applied to determine platelet-associated immunoglobulins (PAIg) and complement (PAC3) in thrombocytopenias of various etiologies. One hundred and one patients with immune thrombocytopenia (chronic autoimmune, 48; acute autoimmune, 37; Evans syndrome, nine; connective tissue diseases, seven) and 20 patients with presumed nonimmune thrombocytopenia (bone marrow aplasia or malignancy, six; septicemia, five; hypersplenism, five; cirrhosis of liver, three; others, one) were studied. Increased levels of PAIg/C3 were found in 76% of patients with immune thrombocytopenia. PAIgG was raised in 66%, PAIgM in 57%, PAIgA in 44%, and PAC3 in 29%. Isolated elevation of PAIgG and of PAIgM was found in four and three cases, respectively; PAIgA and PAC3 were elevated in one case each. PAIgG was associated with PAIgM in 56%, with PAIgA in 34%, and with PAC3 in 27%. Both patients with Evans' syndrome and patients with connective tissue diseases had significantly higher PAIgM levels than the other patients with immune thrombocytopenia. In patients with nonimmune thrombocytopenia, increased rates of PAIg/C3 were also encountered. Positive test results were found in 88% (PAIgG 88%, PAIgM 47%, PAIgA 35%, and PAC3 24%). In immune-mediated thrombocytopenia, we observed a significant inverse correlation between platelet counts and PAIgG, PAIgA, and PAC3, but not with PAIgM. In contrast, no such correlation was found in patients with nonimmune thrombocytopenia. Our data indicate that the evaluation of neither parameter alone nor the combination of PAIg/C3 will discriminate between immune and nonimmune thrombocytopenia. Preferential coating with certain immunoglobulins, however, may be present in some subgroups of immune thrombocytopenias.

Clinical significance of surface and internal pools of platelet-associated immunoglobulins in immune thrombocytopenia

We have investigated serum platelet bindable IgG(SPBIgG) and platelet-associated IgG(PAIgG) in patients with immune thrombocytopenia (IT) to ascertain the significance of the larger amounts of PAIgG reported both in normals and in patients using homogenized (Total:T-PAIgG) instead of intact platelets (Surface:S-PAIgG). 12 patients, during active immune thrombocytopenia (A-IT), and 18 patients in steroid-induced remission (S-IT), were studied. As control we considered 20 patients with non-immune thrombocytopenia (N-IT) and 29 subjects with normal platelet count. The average positivity of SPBIgG was 41% with a higher percentage in A-IT (66%) than in S-IT (16%). The results of PAIgG also indicate a different behaviour in A-IT and S-IT of surface and cytoplasmatic pools. During A-IT both pools are enhanced with prevalence towards the surface one (S-PAIgG). On the contrary, during steroid-induced remission, despite the normal amount of the S-PAIgG present the internal pool still increases, indicating a steady-state of IT and the possible existence of a platelet phagocytic activity.

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.

Platelet-associated immunoglobulins IgG, IgM, IgA and complement C3c in chronic idiopathic autoimmune thrombocytopenia: relation to the sequestration pattern of 111indium labelled platelets

Levels of platelet-associated immunoglobulins (PAIg) IgG, IgM, IgA and complement C3c were related to parameters of 111Indium-labelled platelet kinetics in 17 patients with chronic idiopathic autoimmune thrombocytopenia (cAITP). Elevated levels of PAIg/C3c were found in 14 patients (82%) (PAIgG n = 13, PAIgM n = 11, PAIgA n = 1, PAC3c n = 5). Only PAIgG correlated with platelet counts (RS = -0.71, p less than 0.01). Mean platelet life span (MLS) was shortened in all patients (median 12.0 h, range 0.3-45.6 h) and correlated with the platelet counts (RS = 0.49, p less than 0.05). MLS was correlated with PAIgG (RS = -0.52, p less than 0.05), but not with PAIgM, PAIgA, or PAC3c. The site of sequestration was splenic in 10 patients and splenic-hepatic in 7 patients. Although no significant correlation between either site of platelet sequestration and any of the investigated PAIg/C3c was demonstrable, platelets coated with higher PAIgG levels were more readily sequestrated in the spleen, while elevations of PAC3c were found in 4 out of 7 patients with hepatic involvement.

Effect of IgG anti-Rho(D) in adult patients with chronic autoimmune thrombocytopenia

Seventeen adult patients with chronic (15 cases) or acute (two cases) autoimmune thrombocytopenia (ITP) were given intravenous and/or intramuscular injections of 0.75-4.5 mg of IgG anti-Rho(D) over a period of 1-5 days. Significant elevations of the platelet count (increments greater than 50 X 10(9)/liter) resulted in 13 of 15 Rh-positive patients but not in either of two Rh-negative patients. Heat-aggregated human albumin given to one of the Rh-negative patients also did not lead to a significant increase of the platelet count. The elevation of the platelet counts in Rh-positive patients after IgG anti-Rho(D) administration was often transient (less than 4 weeks), but long-term benefit (greater than 5 months) was achieved in five cases. The IgG concentration on RBC from five Rh-positive patients studied increased from a usually undetectable value before to approximately 700-1,700 IgG molecules/per RBC after anti-Rho(D) administration resulting in a strongly positive direct antiglobulin test. Nevertheless, an overt clinical hemolysis was seen in only one patient. The clearance of autologous 51Cr-labeled RBC was determined in four patients and was slightly enhanced in three and normal in one splenectomized patient. We conclude that the Fc receptor blockade involved in platelet sequestration was not associated with the induction of significant RBC clearance and that a reversible interaction of sensitized RBC with phagocytic cells and/or a low-grade destruction of these cells might be sufficient for the elevation of circulating platelets in the majority of patients with ITP.

Immunoglobulin G is a platelet alpha granule-secreted protein

It has been known for 27 yr that blood platelets contain IgG, yet its subcellular location and significance have never been clearly determined. In these studies, the location of IgG within human platelets was investigated by immunocytochemical techniques and by the response of platelet IgG to agents that cause platelet secretion. Using frozen thin-sections of platelets and an immunogold probe, IgG was located within the alpha-granules. Thrombin stimulation caused parallel secretion of platelet IgG and two known alpha-granule proteins, platelet factor 4 and beta-thromboglobulin, beginning at 0.02 U/ml and reaching 100% at 0.5 U/ml. Thrombin-induced secretion of all three proteins was inhibited by prostaglandin E1 and dibutyryl-cyclic AMP. Calcium ionophore A23187 also caused parallel secretion of all three proteins, whereas ADP caused virtually no secretion of any of the three. From these data and a review of the literature, we hypothesize that plasma IgG is taken up by megakaryocytes and delivered to the alpha-granules, where it is stored for later secretion by mature platelets.

Platelet associated immunoglobulins in primary biliary cirrhosis: a cause of thrombocytopenia?

Thrombocytopenia in cirrhotic patients is usually attributed to splenic pooling whereas in idiopathic thrombocytopenic purpura it is related to platelet bound immunoglobulin (PA-IgG). Since primary biliary cirrhosis (PBC) is an autoimmune disorder we have undertaken a prospective study to assess the frequency and possible relationship of PA-IgG to thrombocytopenia in this condition. Sixty-two primary biliary cirrhosis patients (28 precirrhotic; 34 cirrhotic) were studied. Twenty-five patients (40%) had raised PA-IgG of whom 18 had cirrhosis. There was a significant inverse correlation between platelet count and PA-IgG (p less than 0.001) and between platelet count and spleen size (p less than 0.001). Thrombocytopenia (platelets less than 100 X 10(9)/l) was found in nine patients (15%); all nine had raised PA-IgG and eight were cirrhotic with an enlarged spleen. Two cirrhotic patients with persistent thrombocytopenia and bleeding episodes were treated with prednisolone and showed a useful therapeutic response. These results suggest that immune mediated platelet destruction and splenic pooling of platelets may both play a part in the thrombocytopenia observed in primary biliary cirrhosis.

Intravenous immunoglobulin versus oral corticosteroids in acute immune thrombocytopenic purpura in childhood

In a randomised, multicentre study intravenous IgG was compared with oral corticosteroids in 108 children with untreated acute immune thrombocytopenic purpura. IgG was an efficient treatment with no severe untoward reactions. The effects of corticosteroids and IgG were identical for rapid responders, who accounted for 62% of all patients. In contrast, patients requiring more than initial treatment responded better if randomised to IgG. The serum IgG level increased two-fold after IgG. A significant rise in IgM levels was observed after both IgG and corticosteroids. The platelet-associated IgG index was high in 75% of all patients. No significant differences between the two treatment groups were found, but rapid responders had a smaller mean initial platelet-associated IgG index which returned more rapidly and more permanently to normal than that of slow responders.

Platelet-associated complement in chronic ITP

Chronic ITP is due to antibody-induced destruction of platelets by the reticuloendothelial (RE) system. The role of complement in this process is unclear. We measured platelet-associated complement (PAC) components C3, C3bi, C4 and C9 in 16 patients with chronic ITP, in two of these patients prior to and after splenectomy. Competitive solid-phase radioimmunoassays using monoclonal antibody (anti-C3d, anti-C3bi neoantigen or anti-C9) or affinity-purified heterologous antibody (anti-C4) were used. Mean values (+/- SD) of normal subjects (ng/10(7) plts) were: PAC3d 17.6 +/- 6.8; PAC3bi 11.6 +/- 2.3; PAC4 1.6 +/- 0.5; PAC9 9.9 +/- 2.6. Significantly elevated (greater than 2 SD) PAC3, PAC3bi, PAC4 and PAC9 levels occurred in 12/16, 11/14, 10/14 and 5/9 chronic ITP patients. The PAC3, PAC3bi and PAC9 values correlated inversely with the patients' platelet counts (P less than 0.001); PAC4 levels did not. A positive correlation was also noted between PAC3, PAC3bi and PAC9 while PAC4 values showed no correlation. Two patients with preoperative elevation of all four PAC proteins showed normalization of PAC3, PAC3bi and PAC9 values after a splenectomy-induced remission; PAC4 levels remained elevated for up to 5 months after surgery. We conclude that in vivo C activation occurs in most chronic ITP patients with binding of C3 and C9 to the platelet surface. This in vivo C activation may promote more efficient phagocytosis (C3b) and possibly platelet lysis (C5-9) in some ITP patients.

Platelet antibodies of the IgM class in immune thrombocytopenic purpura

The clinical course and response to therapy of patients with immune thrombocytopenic purpura (ITP) are not completely determined by the level of IgG present on the platelet surface. It is possible that antibodies of other immunoglobulin classes also play a role in platelet destruction in some of these patients. Therefore, we studied 175 patients with ITP for the presence of IgM anti-platelet antibodies using radiolabeled polyclonal or monoclonal anti-IgM. We observed that 57% of patients with clinical ITP had increased levels of IgM on their platelets, compared with normal controls and patients with thrombocytopenia who did not have ITP (less than 10%), (P less than 0.01). We obtained similar results using either radiolabeled polyclonal or monoclonal anti-IgM, reagents whose integrity was first characterized using erythrocytes coated with defined amounts of IgM antibody. Among patients with increased platelet-IgM there was a significant correlation both with the presence of increased platelet-C3 as well as the amount of platelet-C3 (P less than 0.01, r = 0.53). We demonstrated the presence of warm-reacting IgM anti-platelet antibodies in the plasma of two of these patients who were further studied. The isolated IgM fraction from these two plasmas was able to activate complement and place 3H-C3 on normal platelets. These studies demonstrate the presence of warm-reacting IgM anti-platelet antibodies in some patients with ITP. They suggest that the binding of complement to platelets by IgM antibodies may initiate platelet clearance as well as enhance the effect of IgG antibodies in ITP.

Platelet associated immunoglobulins (PAIgG and PAIgM) in autoimmune thrombocytopenia

An enzyme linked assay system was used to quantitate platelet associated IgM (PAIgM) in addition to platelet associated IgG (PAIgG) in normal subjects and in 145 patients with autoimmune thrombocytopenia (AITP). The mean PAIgM level in normals was 1.17 ng/10(6) platelets with a range of 0.01-2.45 ng (mean +/- 2 SD). The corresponding PAIgG values as follows: mean 6.0 ng, range 2.0-10 ng/10(6) platelets. Elevated PAIgG was seen in 67.6% and abnormally raised PAIgM in 79.3% of patients. Both values were raised together in 57.2% and either elevated PAIgG or PAIgM in 89.7%. All patients with PAIgG values greater than 4 times upper limit of normality were found to have abnormal PAIgM. The relevance of elevated PAIgM, the possible interaction between PAIgG and PAIgM and the implication of our results in patients with autoimmune thrombocytopenia are discussed.

Measurement of platelet life-span in normal subjects and patients with myeloproliferative disease with indium oxine labelled platelets

The use of 111Indium oxine as a platelet label for the performance of platelet life-span studies has been examined. Platelet life-span in normal subjects varied between 8 X 10 and 10 X 36 d. Patients with primary thrombocythaemia had clearly reduced platelet life-span whether or not they presented with vascular occlusion and this abnormality persisted after reduction of the platelet count to normal by busulphan therapy. Patients with similarly elevate platelet counts due to chronic granulocytic leukaemia or after splenectomy had platelet life-span values in the normal range. Plasma beta-TG levels could not be used to predict platelet life-span in these groups of patients. Measurement of platelet life-span using 111Indium labelled platelets is a useful technique in the examination of platelet function in occlusive vascular disease.

Treatment of autoimmune thrombocytopenic purpura with rhesus antibodies (anti-Rh0(D)

There is evidence that blockade of the reticuloendothelial system (RES) by sequestration of autologous red blood cells (RBC) leads to an elevation of platelet counts in immune thrombocytopenia. To substantiate this hypothesis, 10 Rh0(D)-positive adult patients (9 female, 1 male) with chronic autoimmune thrombocytopenic purpura (ITP) (1 to 21 years duration) were treated with low doses of intravenous IgG-anti-Rh0(D) (200 to 1,000 micrograms per dose; 300 to 3,600 micrograms per course; administration within 1 to 5 days). All patients improved clinically as indicated by cessation of bleeding. In eight out of ten patients there was a rise in platelet count. Platelet increments were excellent (greater than 100 X 10(9)/l) in one, good (50-100 X 10(9)/l) in three, fair (20-50 X 10(9)/1) in two and low (10-20 X 10(9)/1) in two patients. Splenectomized patients (N = 4) had a poorer response than non-splenectomized patients (N = 6) with mean increments of 16 X 10(9)/l (range 5-43 X 10(9)/l) versus 60 X 10(9)/l (range 10-110 X 10(9)/l). The increase in platelet counts persisted for seven to over 150 days. Transient and slight signs of haemolysis developed in seven out of ten patients (haemoglobin remained stable; increase of lactate dehydrogenase (greater than 250 IU/l) in four, decrease of haptoglobin (less than 60 mg/dl) in five patients). The direct antiglobulin test became positive in all cases due to IgG1 without complement fixation. We conclude that the interaction of antibody-coated RBC with macrophages (and, probably, other means of RBC alteration) is a feasible therapeutic approach in selected cases of ITP and related conditions.

Platelet-associated IgG in hepatitis and cirrhosis

Increasing evidence is accumulating which indicates that immunological abnormalities contribute to the development of liver disease and its signs and symptoms. Platelet-associated IgG (PAIgG) levels were quantified in 42 patients with biopsy-proven liver disease of various etiologies to determine the relationship of thrombocytopenia to immunologic abnormalities in these disorders. Five of six nonthrombocytopenic patients with acute viral hepatitis B had elevated PAIgG. Six of ten patients with chronic active hepatitis had elevated PAIgG and thrombocytopenia. In contrast, only one of six patients with chronic persistent hepatitis had elevated PAIgG. Nine of ten patients with alcoholic hepatitis had elevated PAIgG; seven of the nine were thrombocytopenic. Seven of ten alcoholic patients with cirrhosis had elevated PAIgG; six of seven were thrombocytopenic. Thus the increase in PAIgG may be present without thrombocytopenia in acute liver injury, while patients with chronic persistent hepatitis do not usually exhibit this abnormality. Severe chronic active liver disease is accompanied by thrombocytopenia and an increase in PAIgG levels.

Platelet-associated complement C3 in thrombocytopenic states

Platelet-associated complement components C3, C3d and C4 (PAC3, PAC3d, PAC4) were quantitated by a modification of the platelet radioactive anti-IgG test using highly purified C3 antibodies in 74 patients with immune thrombocytopenia (ITP), 26 patients with presumed nonimmune thrombocytopenia (NTP), and 114 normal individuals. Elevated PAC3 levels were found in 26 out of 74 patients with ITP (35%) and in 10 out of 26 patients with NTP. Although the percentage of elevated PAC3 values was higher in thrombocytopenic patients than in nonthrombocytopenic patients, no statistically significant correlation existed between platelet counts and PAC3 levels, neither for ITP nor for NTP. However, such a relationship was demonstrable between PAC3 and platelet-associated IgG, both for ITP (P less than 0.05) as well as NTP patients (P less than 0.001). We conclude that elevated PAC3 values are not restricted to immune thrombocytopenias. Quantitative differences of PAC3 between ITP and NTP patients suggest that part of the PAC3 is immunologically mediated and has a role in the pathogenesis of autoimmune thrombocytopenias.