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

Primary Immune Thrombocytopenic Purpura (ITP) and ITP Associated with Systemic Lupus Erythematosus: A Review of Clinical Characteristics and Treatment Modalities

Immune thrombocytopenic purpura (ITP) is an immune-mediated disorder characterized by the destruction of platelets and megakaryocytes due to autoantibodies against the platelet surface proteins. ITP without any apparent cause of thrombocytopenia is defined as primary ITP, and ITP in the setting of SLE is secondary ITP, which can be diagnosed after excluding other causes of thrombocytopenia by history, physical examination, and laboratory testing. Patients with ITP associated with SLE have higher median platelet count and less bleeding manifestations compared to the patients with primary ITP. It can be very challenging to diagnose primary ITP in SLE patients as other causes of thrombocytopenia including drug-induced thrombocytopenia, antiphospholipid syndrome, and thrombotic microangiopathic process should be ruled out. Corticosteroids are the main modality of treatment. IVIG can be used in severe cases. Splenectomy was found to be less effective in ITP associated with SLE compared to primary ITP. Control of disease activity with immunosuppressive therapy can be helpful in some cases associated with active disease flares in SLE patients.

Evolution and Utility of Antiplatelet Autoantibody Testing in Patients with Immune Thrombocytopenia

To this day, immune thrombocytopenia (ITP) remains a clinical diagnosis made by exclusion of other causes for thrombocytopenia. Reliable detection of platelet autoantibodies would support the clinical diagnosis, but the lack of specificity and sensitivity of the available methods for platelet autoantibody testing limits their value in the diagnostic workup of thrombocytopenia. The introduction of methods for glycoprotein-specific autoantibody detection has improved the specificity of testing and is acceptable for ruling in ITP but not ruling it out as a diagnosis. The sensitivity of these assays varies widely, even between studies using comparable assays. A review of the relevant literature combined with our own laboratory's experience of testing large number of serum and platelet samples makes it clear that this variation can be explained by variations in the characteristics of the tests, including in the glycoprotein-specific monoclonal antibodies, the glycoproteins that are tested, the platelet numbers used in the assay and the cutoff levels for positive and negative results, as well as differences in the tested patient populations. In our opinion, further standardization and optimization of the direct autoantibody detection methods to increase sensitivity without compromising specificity seem possible but will still likely be insufficient to distinguish the often very weak specific autoantibody signals from background signals. Further developments of autoantibody detection methods will therefore be necessary to increase sensitivity to a level acceptable to provide laboratory confirmation of a diagnosis of ITP.

The non-haemostatic role of platelets in systemic lupus erythematosus

Dysregulation of lymphocyte function, accumulation of autoantibodies and defective clearance of circulating immune complexes and apoptotic cells are hallmarks of systemic lupus erythematosus (SLE). Moreover, it is now evident that an intricate interplay between the adaptive and innate immune systems contributes to the pathogenesis of SLE, ultimately resulting in chronic inflammation and organ damage. Platelets circulate in the blood and are chiefly recognized for their role in the prevention of bleeding and promotion of haemostasis; however, accumulating evidence points to a role for platelets in both adaptive and innate immunity. Through a broad repertoire of receptors, platelets respond promptly to immune complexes, complement and damage-associated molecular patterns, and represent a major reservoir of immunomodulatory molecules in the circulation. Furthermore, evidence suggests that platelets are activated in patients with SLE, and that they could contribute to the circulatory autoantigenic load through the release of microparticles and mitochondrial antigens. Herein, we highlight how platelets contribute to the immune response and review evidence implicating platelets in the pathogenesis of SLE.

ANA Negative Systemic Lupus Erythematosus Leading to CTEPH, TTP-Like Thrombocytopenia, and Skin Ulcers

SLE affects almost every organ system, with differing degrees of severity. During its clinical course periods of flares may alternate with periods of remission culminating in disease and therapy related damage. We describe a case of ANA negative SLE with severe thrombocytopenia, cutaneous vasculitis, antiphospholipid antibody syndrome, and pulmonary artery hypertension. As there is no definitive cure for SLE the treatment lies in caring for the individual organ systems involved and simultaneously taking care of the patient as a whole.

Haematological manifestations of lupus

Our purpose was to compile information on the haematological manifestations of systemic lupus erythematosus (SLE), namely leucopenia, lymphopenia, thrombocytopenia, autoimmune haemolytic anaemia (AIHA), thrombotic thrombocytopenic purpura (TTP) and myelofibrosis. During our search of the English-language MEDLINE sources, we did not place a date-of-publication constraint. Hence, we have reviewed previous as well as most recent studies with the subject heading SLE in combination with each manifestation. Neutropenia can lead to morbidity and mortality from increased susceptibility to infection. Severe neutropenia can be successfully treated with granulocyte colony-stimulating factor. While related to disease activity, there is no specific therapy for lymphopenia. Severe lymphopenia may require the use of prophylactic therapy to prevent select opportunistic infections. Isolated idiopathic thrombocytopenic purpura maybe the first manifestation of SLE by months or even years. Some manifestations of lupus occur more frequently in association with low platelet count in these patients, for example, neuropsychiatric manifestation, haemolytic anaemia, the antiphospholipid syndrome and renal disease. Thrombocytopenia can be regarded as an important prognostic indicator of survival in patients with SLE. Medical, surgical and biological treatment modalities are reviewed for this manifestation. First-line therapy remains glucocorticoids. Through our review, we conclude glucocorticoids do produce a response in majority of patients initially, but sustained response to therapy is unlikely. Glucocorticoids are used as first-line therapy in patients with SLE with AIHA, but there is no conclusive evidence to guide second-line therapy. Rituximab is promising in refractory and non-responding AIHA. TTP is not recognised as a criteria for classification of SLE, but there is a considerable overlap between the presenting features of TTP and SLE, and a few patients with SLE have concurrent TTP. Myelofibrosis is an uncommon yet well-documented manifestation of SLE. We have compiled the cases that were reported in MEDLINE sources.

Anti-glycoprotein IIb/IIIa autoantibodies are reversibly internalized into platelets in idiopathic (autoimmune) thrombocytopenic purpura

We used flow cytometry to investigate the binding of platelet-binding IgG (PBIgG) to unfixed platelets in idiopathic thrombocytopenic purpura (ITP), including that of anti-glycoprotein (GP) IIb/IIIa antibodies. Anti-GPIIb/IIIa antibodies were detected in 13/64 ITP patients using antigen-capture ELISA and immunoblotting. When unfixed platelets were incubated with ITP plasma, the PBIgG level was significantly higher than after incubation with normal plasma. When 1 microM ADP was added to unfixed platelets, which were incubated with ITP plasma and washed, the PBIgG level increased additively. GMP-140 is a constituent of platelet alpha-granules, and a monoclonal antibody directed against this protein showed weak binding to platelets after 1 microM ADP stimulation. The increase of PBIgG produced by ADP was significantly greater when ITP plasma positive for anti-GPIIb/IIIa antibody was used compared with that obtained using antibody-negative ITP plasma. This increase of PBIgG was markedly inhibited by the removal of extracellular calcium with EDTA or the dissociation of the GPIIb/IIIa complex by EDTA treatment at 37 degrees C. These results suggest that anti-GPIIb/IIIa autoantibodies are internalized by unfixed ITP platelets and stored somewhere other than the alpha-granules. This stored antibody pool can be reversibly redistributed on the platelet surface by weak stimulants such as ADP and a functional GPIIb/IIIa complex appears to be necessary for this to occur.

Clinical significance of platelet-associated immunoglobulins in narcotic addicts with human immunodeficiency virus infection

Increased amounts of platelet-associated immunoglobulin G (PAIgG) have been reported in human immunodeficiency virus (HIV)-infected patients with thrombocytopenia. We have prospectively investigated PAIgG in 21 asymptomatic (group A; CDC stages IIA-IIB) and 9 symptomatic (group B: CDC stages IIIB-IV) HIV-infected narcotic addicts. In both groups only two subjects presented with a decreased platelet count. By competitive ELISA, we found a 1.8- and 2.3-fold greater total PAIgG (PAIgGtot) as measured on platelet lysates in group A and B, respectively; surface-bound IgG (PAIgGsurf) as measured on intact platelets was 2.5- and 3.0-fold greater in groups A and B, respectively, as compared to 36 controls. The ratio between PAIgGtot and PAIgGsurf was lower in HIV-infected addicts when compared to controls (P less than 0.05). This indicates that platelets from HIV-infected subjects not only have increased surface and internal pools of PAIgG, but also present with a distribution between these two pools that differs from that of normal platelets. In addition, levels of circulating immune complexes (CIC) were abnormally raised in 17/21 (81%) subjects of group A in 6/9 (66%) subjects of group B.

Relative importance of total versus external platelet-associated IgG

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 ELI-SA 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.