Megathrombocytes, platelet regeneration time and platelet associated IgG in idiopathic thrombocytopenic purpura and in thrombocytopenia associated with chronic liver disease

Platelet production and destruction in liver cirrhosis

BACKGROUND & AIMS

Thrombocytopenia is common in liver cirrhosis (LC) but the mechanisms are not fully understood. The purpose of our work was to evaluate platelet kinetics in LC with different etiologies by examining platelet production and destruction.

METHODS

Ninety-one consecutive LC patients (36 HCV, 49 alcoholics, 15 HBV) were enrolled. As controls, 25 subjects with idiopathic thrombocytopenic purpura, 10 subjects with aplastic anemia, and 40 healthy blood donors were studied. Plasma thrombopoietin (TPO) was measured by ELISA. Reticulated platelets (RP) were determined using the Thiazole Orange method. Plasma glycocalicin (GC) was measured using monoclonal antibodies. Platelet associated and serum antiplatelet antibodies were detected by flow cytometry. B-cell monoclonality in PBMC was assessed by immunoglobulin fingerprinting.

RESULTS

Serum TPO was significantly lower in LC (29.9±18.1 pg/ml) compared to controls (82.3±47.6 pg/ml). The GC levels were higher in LC (any etiology) than in healthy cases. Conversely, the absolute levels of RP were lower in LC (any etiology) than in healthy controls. The platelet-associated and serum anti-platelet antibodies were higher in HCV+ LC compared to healthy subjects (p<0.0064), alcoholic LC (p<0.018), and HBV+ LC (p<0.0001). B-cell monoclonality was found in 27% of the HCV+LC, while it was not found in HBV+ or alcoholic LC.

CONCLUSIONS

Patients with LC present decreased plasma TPO, accelerated platelet turnover, and reduced platelet production. This indicates that LC thrombocytopenia is a multifactorial condition involving both increased platelet clearance and impaired thrombopoiesis.

A role of autoantibody-mediated platelet destruction in thrombocytopenia in patients with cirrhosis

Thrombocytopenia is a common manifestation in patients with liver cirrhosis (LC), but its underlying mechanism remains controversial. This study examined the role of anti-platelet autoimmunity in cirrhotic thrombocytopenia by determining the autoantibody response to GPIIb-IIIa, a major platelet surface autoantigen recognized by anti-platelet antibodies in patients with idiopathic thrombocytopenic purpura (ITP). Circulating B cells producing anti-GPIIb-IIIa antibodies as well as platelet-associated and plasma anti-GPIIb-IIIa antibodies were examined in 72 patients with LC, 62 patients with ITP, and 52 healthy controls. In vitro anti-GPIIb-IIIa antibody production was induced in cultures of peripheral blood mononuclear cells (PBMCs) by stimulation with GPIIb-IIIa. The frequency of anti-GPIIb-IIIa antibody-producing B cells in patients with LC was significantly greater than in healthy controls (10.9 +/- 6.2 vs. 0.4 +/- 0.3/10(5) PBMCs; P <.0001) and was even higher than the frequency in patients with ITP (8.2 +/- 5.2; P =.007). Anti-GPIIb-IIIa antibodies in the patients with LC and ITP were mainly present on the surfaces of circulating platelets rather than in the plasma in an unbound form. Furthermore, PBMCs from patients with LC and ITP produced anti-GPIIb-IIIa antibodies on antigenic stimulation with GPIIb-IIIa in vitro, and the specific antibodies produced had the capacity to bind normal platelet surfaces. In conclusion, the similar profile of the anti-GPIIb-IIIa autoantibody response in patients with LC and ITP suggests that autoantibody-mediated platelet destruction may contribute at least in part to cirrhotic thrombocytopenia.

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.

Transient deficiency of peripheral blood accessory cells in supporting T cell mitogenesis in patients suffering from chronic idiopathic thrombocytopenic purpura after intravenous gammaglobulin treatment

Mitogenic response of blood lymphocytes to phytohemagglutinin (PHA) and to OKT3 monoclonal antibodies was investigated in 7 patients suffering from chronic idiopathic thrombocytopenic purpura (ITP) before, during and after high-dose intravenous (i.v.) immunogammaglobulin (IgG) infusion. The platelet count rose above the pre-treatment values during infusion therapy in all patients but one. Five out of seven patients presented elevated platelet-associated IgG (PA-IgG) levels at the time of the first infusion; four of these showed an increase in platelet count and a transient reduction or normalization of PA-IgG after IgG infusion. Five out of seven patients showed an impairment of T lymphocyte mitogenic response to PHA and OKT3 before therapy. All patients responded to IgG therapy with a transient deficiency of FcR mediated monocytes (Mo) in supporting T cell mitogenesis induced by both mitogens during and after IgG infusion. This reduced cooperative capability of Mo disappeared at various times after the end of therapy (range 3-12 days). The transient alteration of Mo function, possibly due to a modification in the surface number or in the affinity of Fc-receptors, can explain in part, the increase in platelet count during and after IgSRK infusion.

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 prostaglandin production in alcoholic liver disease

Impaired platelet aggregation is a common finding in patients with alcoholic liver disease. This may be due to impairment of prostaglandin synthesis and alterations in the proportions of platelet membrane lipids secondary to changes in circulating lipids. Platelet prostaglandin synthesis was measured by the production of malonaldehyde (MDA), and was increased in patients with alcoholic cirrhosis compared with normal controls. Mean MDA production in cirrhotics was 3.37 nmoles MDA/10(9) platelets, and in controls 1.01 nmoles MDA/10(9) platelets (p less than 0.01). Platelet prostaglandin synthesis was significantly related to the serum cholesterol:triglyceride ratio (r = 0.73, p less than 0.005). Platelet aggregation was impaired in 12/14 cirrhotics. Five of the cirrhotics had a factor in their plasma which appeared to enhance the aggregation of normal platelets. Impaired platelet aggregation in patients with alcoholic liver disease appears to be due to a defect in intraplatelet metabolism.