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.     

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.     

Platelet-Associated IgG in Acute and Chronic Hepatic Diseases

In order to investigate the role of an immune mechanism in the pathogenesis of thrombocytopenia in hepatic patients, we measured platelet associated IgG (PAIgG) in 84 patients with various hepatic diseases. Increased PAIgG levels were found in 84% of patients with chronic active hepatitis (mean 21.32 ± 8.45 fg/platelet) and in 75% of those with cirrhosis with hepatitis (mean 17.3 ± 11.2 fg/platelet). In these patients there was no significant correlation between PAIgG and platelet count. Increased PAIgG amounts were also observed in some patients with inactive cirrhosis (18%). Normal PAIgG values were found in all patients with acute viral hepatitis and chronic persistent hepatitis. An immunologic mechanism may play a role in the pathogenesis of thrombocytopenia in hepatic patients. Furthermore, measurement of PAIgG may have a great usefulness in the differential diagnosis of chronic hepatic diseases.     

Direct quantitation of platelet-associated IgG by electroimmunoassay

An electroimmunoassay was applied to the quantitation of platelet- associated IgG (PAIgG). Protein solubilized by Triton X100 from washed platelets was electrophoresed at pH 5.0 in agarose gels containing carbamoylated rabbit anti-human IgG (pI approximately equal to 5.0). Because the rabbit antibody is immobilized under these conditions, while PAIgG is freely mobile, rocket precipitates were produced, the heights of which were directly proportional to the amount of antigen (PAIgG) present. By this method, PAIgG for normal individuals was found to be 4.3 +/- 1.7 fg/platelet (mean +/- 2 SD; n = 35). Increased PAIgG levels (direct assay) were found in 27 of 29 patients with a diagnosis of clinically active idiopathic thrombocytopenic purpura (ITP), ranging from 10.5 to 101.5 fg/platelet. Moderately elevated PAIgG was found in 8 of 10 patients in an early stage of recovery from ITP (range 7.5-9.5 fg/platelet) and in 3 of 6 patients with apparent nonimmune thrombocytopenia (range 14.5-24.0 fg/platelet). Electroimmunoassay for PAIgG can be performed on patients with platelet counts as low as 2000/microliters, yields results in less than 24 hr, is highly reproducible, and appears to provide a useful tool for the evaluation of patients with immunologically mediated thrombocytopenia.     

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

S ummary . Platelet-associated IgG (PAIgG), platelet mean life span (MLS), and platelet sequestration sites were studied in 69 patients with immune (ITP) and presumed nonimmune thrombocytopenias (NTP). A shortened MLS was associated with elevated PAIgG (N=46), and with normal PAIgG (N=15), Four patients had a normal MLS, but elevated PAIgG, four patients were normal for both parameters. The highest PAIgG values occurred in ITP patients with a very short MLS. Nine NTP patients had also elevated PAIgG, but a normal or slightly shortened MLS. There was a significant double log correlation between PAIgG and MLS for ITP, but not for NTP patients. Judged from the coefficient of determination, only 10% of PAIgG were directly related to a shortened MLS.
70% of patients (N= 63) had exclusively splenic and 30% hepatosplenic sequestration. PAIgG was elevated in 29/44 patients with splenic (66%) and in 16/19 patients with hepatosplenic sequestration (84%). In ITP, PAIgG-positive cases were observed in 69% of splenic v 82% of hepatosplenic sequestration, while in NTP the corresponding figures were 6/11 and 2/2. No significant correlation between PAIgG and either sequestration type was demonstrable.
We conclude that in immunologically mediated thrombocytopenia only a small portion of PAIgG accounts for a decreased MLS, and that the concentration of PAIgG per se does not determine the platelet sequestration type.     

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.     

Flow cytometric analysis of platelets from childrenwith the Wiskott-Aldrich syndrome reveals defects in platelet development, activation and structure

The pathophysiology of platelet dysfunction in the Wiskott-Aldrich immune deficiency syndrome (WAS) remains unclear. Using flow cytometry, we have characterized the functional properties of platelets from 10 children with WAS. Patients with WAS had thrombocytopenia, small platelets, increased platelet-associated IgG and reduced platelet-dense granule content. Levels of reticulated 'young' platelets were normal in the WAS patients. Although the mean numbers of platelet glycoprotein (GP) Ib, GPIIbIIIa and GPIV molecules per platelet appeared lower in WAS patients than in healthy controls, analysis of similar-sized platelets revealed the mean number of GPIb molecules per platelet to be comparable in patients and normal controls. Surface GPIIbIIIa and GPIV expression was, however, significantly lower on the WAS platelets than on normal platelets. Compared with normal platelets, WAS platelets showed a reduced ability to modulate GPIIbIIIa expression following thrombin stimulation. In addition, thrombin- and ADP-induced expression of CD62P and CD63 was defective in WAS platelets. Phallacidin staining of the WAS platelets revealed less F-actin content than in normal platelets. Together, these data suggest that the reduced platelet number and function in WAS reflects, at least in part, a defect in bone marrow production as well as an intrinsic platelet abnormality.     

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.     

Platelet-associated IgG in immune thrombocytopenic purpura

A method for the measurement of immunoglobulin G associated with gel- filtered platelets is described and finding in 70 control subjects and 37 patients with immune thrombocytopenic purpura (ITP) are reported. Control platelet-associated IgG (PAIgG) levels (nanograms IgG per 10(9) platelets) averaged (+/-SD) 1231+/-424; samples studied after 24 and 48 hr remained within the control range. PAIgG values of 19 adult and 12 childhood patients with chronic ITP averaged 4711+/-3025 and 4923+/- 3955, respectively, and differed significantly from controls (p less than 0.001). There was an inverse correlation between PAIgG values and the chronic ITP patient's platelet count. Six patients with childhood acute ITP had PAIgG levels ranging from 5588 to 56,250 and appeared to represent a different statistical population from those with chronic ITP. In chronic ITP patients responding to splenectomy, there was an immediate normalization of PAIgG levels; however, a certain percentage of patients studied several months after splenectomy evidenced elevated PAIgG levels in association with normal platelet counts. These data showed that the direct measurement of platelet associated antibody is a useful technique in the diagnosis and follow-up of patients with chronic ITP. Preliminary studies in patients with acute ITP have suggested that this method may be useful in differentiating acute and chronic childhood 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.     

The relationship among platelet-associated IgG, platelet lifespan, and reticuloendothelial cell function

Platelet-associated IgG (PAIgG) has been reported to be elevated in nonthrombocytopenic patients who have a normal platelet lifespan. This has been interpreted as indicating that PAIgG is a nonspecific finding in these patients and not a determinant of platelet survival. It is important to recognize that the reticuloendothelial (RE) system plays an important role in the clearance of antibody-sensitized cells. In this study, we related the level of PAIgG and the platelet lifespan to the RE function in patients with: (A) idiopathic thrombocytopenic purpura (ITP), and (B) five patients with elevated levels of PAIgG yet normal or near-normal platelet counts. RE function was assessed by measuring the clearance of autologous chromium-labeled red cells sensitized with a precise amount of alloantibody (2,000-3,600 molecules of IgG/cell). Eight patients with immune thrombocytopenia had significantly shortened platelet survivals (less than 2-113 hr). In contrast, the five patients with elevated PAIgG, yet normal or near- normal platelet counts, all had normal autologous platelet survivals (186-222 hr). These patients also had significantly impaired clearance of IgG-sensitized red cells, with an average of 85% of the infused red cells remaining in the circulation at 60 min (normal 42% +/- 14%, n = 10). In this study, every patient with elevated PAIgG and normal RE function had a shortened platelet lifespan. Those patients with elevated PAIgG and impaired RE function did not invariably have a shortened platelet lifespan. The observation that the PAIgG is elevated in some patients whose platelet survival is normal does not indicate that PAIgG is not biologically relevant. It indicates that these patients may have RE blockade and do not clear IgG-sensitized cells.     

111In-oxine platelet survivals in thrombocytopenic infants

Thrombocytopenia is a common occurrence (20%) in sick neonates, but the causes have not been well studied. In this report we demonstrate that thrombocytopenia in the neonate is characterized by increased platelet destruction as shown by shortened homologous 111In-oxine-labeled platelet life spans. Thirty-one prospectively studied thrombocytopenic neonates were investigated by measuring the 111In-labeled platelet life span, platelet-associated IgG (PAIgG), and coagulation screening tests. In every infant, the thrombocytopenia was shown to have a destructive component since the mean platelet life span was significantly shortened to 65 +/- 6 (mean +/- SEM) hours with a range of one to 128 hours compared with adult values (212 +/- 8; range, 140 to 260; gamma function analysis). The platelet survival was directly related to the lowest platelet count and inversely related to both the highest mean platelet volume and duration of the thrombocytopenia. In 22 infants the percent recovery of the radiolabeled platelets was less than 50%, which suggested that increased sequestration also contributed to the thrombocytopenia. Infants with laboratory evidence of disseminated intravascular coagulation (n = 8) or immune platelet destruction evidenced by elevated levels of PAIgG (n = 13) had even shorter platelet survivals and a more severe thrombocytopenia compared with the ten infants in whom an underlying cause for the thrombocytopenia was not apparent. Full-body scintigraphic images obtained in 11 infants showed an increased uptake in the spleen and liver, with a spleen-to- liver ratio of 3:1. This study indicates that thrombocytopenia in sick neonates is primarily destructive, with a subgroup having evidence of increased platelet sequestration.     

Effect of paraformaldehyde on platelet size and on measurement of surface IgG

In many platelet assays, as in measurement of platelet-adherent IgG (PAIgG), platelets are fixed in paraformaldehyde (PFA). To better clarify the effect of PFA on platelet size and on PAIgG measurement we compared PAIgG levels in a series of 40 samples, with or without PFA fixing. We used an ELISA which was set up on unfixed platelets and gave excellent results in terms of linearity ( r = 0.923), precision (mean CV = 5%) and correlation with a platelet suspension immunofluorescence test. We found PAIgG values in unfixed platelets were about 10-fold higer than in PFA-fixed (0.411 - 0.172 fg/platelet vs. 0.035 - 0.019 fg/platelet). This discrepancy could be a consequence of the smaller mean platelet volume (MPV) of washed platelets when fixed in PFA (8.0 - 0.8 fl as compared to 10.1 - 1.07). This effect of PFA could decrease the amount of binding sites for IgG exposed on the platelet membrane and hence explain the significantly lower PAIgG values observed in fixed platelets. The PAIgG measurements on unfixed platelets from 200 healthy subjects displayed a Gaussian distribution with a mean - SD of 0.32 - 0.13 fg/platelet, i.e., 1200 - 500 molecules/platelet.     

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.     

A double antibody radioassay for the detection of platelet associated IgG

A double antibody radioimmunoassay has been developed for the detection of platelet associated IgG (PAIgG). The assay employs conventional radioassay technology and, as such, readily may be adopted by laboratories familiar with radioassay techniques. The assay is sensitive to 0.6 ng IgG and can be undertaken on 10⁶-10⁷ platelets, or fewer in the case of thrombocytopenia with raised PAIgG. The assay can be completed within 2 working days. Normal PAIgG levels in EDTA blood were 0.8 to 5.7 μg IgG/10⁹ platelets. However, normal levels depended upon the anticoagulant used for blood collection and were on average five-fold higher for blood taken into EDTA than for blood taken into ACD; normal range 0.1–1.2 μg/IgG 10⁹ platelets. PAIgG was assayed on blood taken simultaneously into ACD and EDTA from 15 patients with chronic idiopathic thrombocytopenia (ITP). PAIgG was raised in 14 out of 15 EDTA samples, but in only 11 of 15 ACD samples. EDTA was therefore regarded as the anticoagulant of choice. A total of 20 of 23 (87%) patients with chronic ITP had PAIgG values above the normal range. The PAIgG in chronic ITP was weakly related to platelet count, weakly and inversely related to platelet volume, but was independent of serum IgG concentration.     

The value of platelet-associated IgG in predicting the efficacy of splenectomy in autoimmune thrombocytopenia

In a prospective study, the hypothesis of whether the quantitative determination of platelet-associated IgG (PAIgG) in patients with chronic autoimmune thrombocytopenic purpura (ATP) can predict the efficacy of splenectomy, was investigated. PAIgG levels were repeatedly determined in 16 patients with definite ATP pre- and postsplenectomy, and related to platelet counts and platelet mean life span. It was found that patients with an immediate remission after splenectomy tended to have lower PAIgG levels (less than 6%) than failures, but this difference was not statistically significant. We conclude that PAIgG is of limited value for the prediction of the efficacy of splenectomy in ATP.     

Effect of paraformaldehyde on platelet size and on measurement of surface IgG

In many platelet assays, as in measurement of platelet-adherent IgG (PAIgG), platelets are fixed in paraformaldehyde (PFA). To better clarify the effect of PFA on platelet size and on PAIgG measurement we compared PAIgG levels in a series of 40 samples, with or without PFA fixing. We used an ELISA which was set up on unfixed platelets and gave excellent results in terms of linearity (r = 0.923), precision (mean CV = 5%) and correlation with a platelet suspension immunofluorescence test. We found PAIgG values in unfixed platelets were about 10-fold higher than in PFA-fixed (0.411 +/- 0.172 fg/platelet vs. 0.035 +/- 0.019 fg/platelet). This discrepancy could be a consequence of the smaller mean platelet volume (MPV) of washed platelets when fixed in PFA (8.0 +/- 0.8 fl as compared to 10.1 +/- 1.07). This effect of PFA could decrease the amount of binding sites for IgG exposed on the platelet membrane and hence explain the significantly lower PAIgG values observed in fixed platelets. The PAIgG measurements on unfixed platelets from 200 healthy subjects displayed a Gaussian distribution with a mean +/- SD of 0.32 +/- 0.13 fg/platelet, i.e., 1200 +/- 500 molecules/platelet.     

Laparoscopic splenectomy for immune thrombocytopenia (ITP) patients with platelet counts lower than 1 × 109/L

Laparoscopic splenectomy (LS) has become the gold-standard surgical intervention for the treatment of immune thrombocytopenia (ITP) and the patients who experienced medical relapse to steroid. Fewer series are available regarding LS for patients with an extremely low platelet count. The aim of this study is to investigate the feasibility and safety of laparoscopic splenectomy in the treatment of patients with a preoperative platelet count of less than 1 × 109/L. From April 2006 to Jan 2011, 10 patients were managed by laparoscopic splenectomy for idiopathic thrombocytopenia with an extremely low preoperative platelet count. Preoperative, perioperative, and postoperative medical management has been reviewed. Before laparoscopic splenectomy, all of the 10 patients had a platelet count of less than 1 × 109/L but a normal level of coagulation function. Emergency laparoscopic splenectomy was performed. The mean operating time was 157 min; the mean intraoperative blood loss was 44 mL. During the operations, transfusion was provided in two patients. No intraoperative complications ensued. The patients were followed up for a mean of 28 months and showed good recovery without any postoperative complications. Laparoscopic splenectomy is a feasible technique in the treatment of ITP patients, characterized by severe mucocutaneous bleeding, extremely low platelet count, and normal prothrombin time (PT) and activated partial thromboplastin time (APTT).     

Cyclic thrombocytopenia associated with IgM anti-GPIIb-IIIa autoantibodies

Summary. We studied a female patient with cyclic fluctuation in platelet count following splenectomy for autoimmune thrombocytopenia. The cyclical fluctuation appeared to be in phase with her menstrual cycle and her platelet count was low during menses. Bone marrow examinations performed at the peak as well as the bottom of the platelet count showed normal or increased numbers of megakaryocytes. The patient's platelet count increased rapidly after intravenous gamma-globulin (IVIgG) therapy, suggesting that a failure of platelet production is unlikely to account for the cycle. Platelet-associated IgM (PAIgM) was markedly elevated, whereas PAIgG was normal at any stage of the cycle. MACE assay demonstrated that PAIgM contained IgM anti-glycoprotein (GP) IIb-IIIa autoantibodies. Comparison between MACE assay using untreated and EDTA-treated platelets at 3 7°C demonstrated that the platelet-associated IgM autoantibodies mainly recognized divalent cation-dependent conformation(s) of GPUb-IIIa. No antibodies were, however, detected in her serum. The levels of IgM anti-GPIIb-IIIa showed an inverse relationship with the platelet count. In spite of the marked increase in platelet count after IVIgG, however, the levels of IgM anti-GPIIb-IIIa remained elevated. These findings suggest that plateletassociated IgM anti-GPIIb-IIIa autoantibodies are of pathogenic significance in this patient.     

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.