The Mechanisms of Action of Intravenous Immunoglobulin and Polyclonal Anti-D Immunoglobulin in the Amelioration of Immune Thrombocytopenic Purpura: What Do We Really Know?

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.

FcγRIV is required for IgG2c mediated enhancement of RBC alloimmunization

Passive immunization with anti-D can prevent maternal alloimmunization to RhD thereby preventing hemolytic disease of the fetus and newborn. Unexpectedly, anti-D fails in some cases and some monoclonal anti-D preparations paradoxically enhances alloimmunization. The underlying mechanisms modulating humoral alloimmunization by anti-D are unknown. We previously reported that IgG antibody subclasses differentially regulate alloimmunity in response to red blood cell (RBC) transfusions in a mouse model; in particular, IgG2c significantly enhanced RBC alloantibody responses. Initial mechanistic studies revealed that IgG2c:RBC immune complexes were preferentially consumed by the splenic dendritic cell (DC) subsets that play a role in RBC alloimmunization. The deletion of activating Fc-gamma receptors (FcγRs) (i.e., FcγRI, FcγRIII, and FcγRIV) on DCs abrogated IgG2c-mediated enhanced alloimmunization. Because DCs express high levels of FcγRIV, which has high affinity for the IgG2c subclass, we hypothesized that FcγRIV was required for enhanced alloimmunization. To test this hypothesis, knockout mice and blocking antibodies were used to manipulate FcγR expression. The data presented herein demonstrate that FcγRIV, but not FcγRI or FcγRIII, is required for IgG2c-mediated enhancement of RBC alloantibody production. Additionally, FcγRI is alone sufficient for IgG2c-mediated RBC clearance but not for increased alloimmunization, demonstrating that RBC clearance can occur without inducing alloimmunization. Together, these data, combined with prior observations, support the hypothesis that passive immunization with an RBC-specific IgG2c antibody increases RBC alloantibody production through FcγRIV ligation on splenic conventional DCs (cDCs). This raises the question of whether standardizing antibody subclasses in immunoprophylaxis preparations is desirable and suggests which subclasses may be optimal for generating monoclonal anti-D therapeutics.

Management of Adult Patients with Immune Thrombocytopenia (ITP): A Review on Current Guidance and Experience from Clinical Practice

Immune thrombocytopenia (ITP) is an autoimmune process resulting in increased destruction and inadequate production of platelets that can result in bleeding, fatigue, and reduced health-related quality of life. While treatment is not required for many patients with ITP, the occurrence of bleeding manifestations, severe thrombocytopenia, and requirement for invasive procedures are among the reasons necessitating initiation of therapy. Corticosteroids, intravenous immunoglobulin, and anti-RhD immune globulin are typical first-line and rescue treatments, but these agents typically do not result in a durable remission in adult patients. Most patients requiring treatment therefore require subsequent line therapies, such as thrombopoietin receptor agonists (TPO-RAs), rituximab, fostamatinib, splenectomy, or a number of other immunosuppressive agents. In this focused review, we discuss management of adult ITP in the acute and chronic settings.

New insights into IVIg mechanisms and alternatives in autoimmune and inflammatory diseases

PURPOSE OF REVIEW

Intravenous immunoglobulin (IVIg) is an effective treatment for an increasing number of autoimmune and inflammatory conditions. However, IVIg continues to be limited by problems of potential shortages and cost. A number of mechanisms have been described for IVIg, which have been captured in newly emergent IVIg mimetic and IVIg alternative therapies. This review discusses the recent developments in IVIg mimetics and alternatives.

RECENT FINDINGS

Newly emergent IVIg mimetics and alternatives capture major proposed mechanisms of IVIg, including FcγR blockade, FcRn inhibition, complement inhibition, immune complex mimetics and sialylated IgG. Many of these emergent therapies have promising preclinical and clinical trial results.

SUMMARY

Significant research has been undertaken into the mechanism of IVIg in the treatment of autoimmune and inflammatory disease. Understanding the major IVIg mechanisms has allowed for rational development of IVIg mimetics and alternatives for several IVIg-treatable diseases.

Dissecting the mechanism of action of intravenous immunoglobulin in human autoimmune disease: Lessons from therapeutic modalities targeting Fcγ receptors

Since the first description of the administration of high doses of pooled serum IgG, also referred to as intravenous IgG (IVIg) therapy, as being able to ameliorate various autoimmune diseases, researchers have been investigating which molecular and cellular pathways underlie IVIg activity. Apart from trying to understand the obvious conundrum that IgG can trigger both autoimmune pathology and resolution of inflammation, the rapidly expanding use of IVIg has led to a lack of availability of this primary blood product, providing a strong rationale for developing recombinant alternatives. During the last decade, a tremendous number of novel insights into IVIg activity brought the goal of replacing IVIg within reach, at least in select indications, and has led to the initiation of several clinical trials. At the forefront of this effort is the modulation of autoantibody half-life and blocking access of autoantibodies to fragment cystallizable γ receptors (Fcγ receptors). In this rostrum article, we will briefly discuss current models of IVIg activity, followed by a more specific focus on novel therapeutic avenues that are entering the clinic and may replace IVIg in the future.

Enhancement of the blood-circulation time and performance of nanomedicines via the forced clearance of erythrocytes

The rapid elimination of nanoparticles from the bloodstream by the mononuclear phagocyte system limits the activity of many nanoparticle formulations. Here, we show that inducing a slight and transient depletion of erythrocytes in mice (~5% decrease in haematocrit) by administrating a low dose (1.25 mg kg^-1) of allogeneic anti-erythrocyte antibodies increases the circulation half-life of a range of short-circulating and long-circulating nanoparticle formulations by up to 32-fold. Treatment of the animals with anti-erythrocyte antibodies significantly improved the targeting of CD4⁺ cells in vivo with fluorescent anti-CD4-antibody-conjugated nanoparticles, the magnetically guided delivery of ferrofluid nanoparticles to subcutaneous tumour allografts and xenografts, and the treatment of subcutaneous tumour allografts with magnetically guided liposomes loaded with doxorubicin and magnetite or with clinically approved 'stealthy' doxorubicin liposomes. The transient and partial blocking of the mononuclear phagocyte system may enhance the performance of a wide variety of nanoparticle drugs.

Inhibition of platelet phagocytosis as an in vitro predictor for therapeutic potential of RBC antibodies in murine ITP

Polyclonal anti-D is a first-line therapy for immune thrombocytopenia (ITP). Monoclonal antibodies are desirable alternatives, but none have yet proven successful despite their ability to opsonize erythrocytes (or red blood cells, RBCs) and cause anemia. Here, we examined 12 murine erythrocyte–specific antibodies of different specificity and subtypes and found that 8 of these antibodies could induce anemia in antigen-positive mice. Of these 8 antibodies, only 5 ameliorated ITP. All antibodies were examined for their in vitro ability to support macrophage-mediated phagocytosis of erythrocytes. Antibodies which supported erythrocyte phagocytosis in vitro successfully ameliorated ITP in vivo. To examine the ability of each antibody to inhibit phagocytosis of platelets, the antibodies were used to sensitize erythrocytes in vitro and these were added to a platelet phagocytosis assay. Antibodies that inhibited platelet phagocytosis in vitro also all ameliorated ITP in vivo. We conclude that inducing anemia is not a sufficient condition for amelioration of ITP but that the antibody’s ability to prevent platelet phagocytosis in vitro predicted its ability to ameliorate ITP. We suggest that inhibition of in vitro platelet phagocytosis may prove to be a valuable tool for determining which erythrocyte antibodies would likely be candidates for clinical use in ITP.

Increased levels of IL-10 and IL-1Ra counterbalance the proinflammatory cytokine pattern in acute pediatric immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune disease which leads to accelerated platelet clearance. We investigated the plasma cytokine, chemokine and growth factor signatures and their clinical significance in pediatric ITP patients during acute, chronic and follow-up stages as well as the effects of intravenous immunoglobulin (IVIg) treatment, by using the Multiplex technology. In acute ITP before and/or after IVIg treatment we found significantly increased plasma levels of the pro- (tumour necrosis factor-α (TNF-α), interleukin IL-15) and anti- (IL-1 receptor antagonist (Ra), IL-10 and the growth factor interferon γ-induced protein (IP-10)) inflammatory cytokines, compared to healthy controls. Except for IL1-Ra, these cytokines decreased to normal levels in chronic patients. In contrast, growth-regulated α protein (GRO) and soluble CD40 ligand (sCD40L), known as platelet-derived molecules, were found to be significantly decreased in acute and increased in chronic ITP patients compared to healthy controls. GRO levels positively correlated with the platelet counts in the follow-up and chronic cohort. Monocyte counts showed a significant positive correlation only with IP-10 levels in acute ITP after IVIg treatment and follow-up patients. Expression levels of mRNAs for macrophage inflammatory protein MIP1-β, IL-1Ra and GRO determined in peripheral blood mononuclear cells (PBMCs) were significantly reduced in both acute and chronic ITP compared to controls. Our findings suggest that the different clinical presentation of acute and chronic pediatric ITP and to a lesser extent the IVIg treatment effects are characterized overall by a counterbalanced cytokine, chemokine and growth factor pattern response that might exert a pathogenic role in this disease.

The use of IVIg in fetal and neonatal alloimmune thrombocytopenia- Principles and mechanisms

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare neonatal disorder that is caused by alloimmunization against platelet antigens during pregnancy. Although rare, affecting only 1 in 1000 live births, it can cause intracranial hemorrhage and other bleeding complications that can lead to miscarriage, stillbirth and life-long neurological complications. One of the gold-standard therapies for at risk pregnancies is the administration of IVIg. Although IVIg has been used in a variety of different disorders for over 40 years, its exact mechanism of action is still unknown. In FNAIT, the majority of its therapeutic effect is thought the be mediated through the neonatal Fc receptor, however other mechanisms cannot be excluded. Due to safety, supply and other concerns that are associated with IVIg use, alternative therapies that could replace IVIg are additionally being investigated. This includes the possibility of a prophylaxis regimen for FNAIT, similarly to what has been successfully used in hemolytic disease of the fetus and newborn for over 50 years.

Decreased expression of FcγRII in active Graves' disease patients

Background

Graves' disease (GD) is a common autoimmune disease characterized by genetic and environmental factors. Fcγ receptors (FcγRs) are involved in several autoimmune disorders through recognizing immunoglobulin (Ig) G antibodies and mediating immune response. The study on the expression of FcγRs in GD patients is scarce. The purpose of this study was to evaluate the expression of three different types of FcγRs in patients with active and remissive GD.

Methods

Blood samples of patients and healthy subjects were collected to analyze the percentage of FcγRI (CD64), FcγRII (CD32), and FcγRIII (CD16) on peripheral blood mononuclear cells (PBMCs) and monocytes by flow cytometry and Western blotting. CD32 isotypes were also examined in cases and controls by real‐time PCR.

Results

The cell percentages expressed CD32 and protein expressions of CD32 on PBMCs, and monocytes from patients with active GD were significantly reduced compared to controls and patients with remissive GD. In particular, the expression of CD32B on PBMC was also decreased in active GD patients. However, the cell percentages expressed CD16 and CD64 from PBMCs and monocytes were comparable between three groups. Besides, the percentages of CD14⁺CD32⁺ cells were negatively correlated with TRAb titers in active GD patients (r = −0.5825, P ＜ 0.001).

Conclusion

These results suggested that CD32 may act as a novel marker for active GDs. The expression of monocytic CD32, in particular CD32B, in GD patients might play a crucial role in maintaining FcγRs function and be a therapeutic target in GD patients.

Sweet SIGNs: IgG glycosylation leads the way in IVIG-mediated resolution of inflammation

A hallmark of many chronic inflammatory and autoimmune diseases is that there is an impaired resolution of inflammation and return to the steady state. The infusion of high doses of pooled serum IgG preparations from thousands of donors [intravenous immunoglobulin (IVIG) therapy] has been shown to induce resolution of inflammation in a variety of chronic inflammatory and autoimmune diseases, suggesting that IgG molecules can instruct the immune system to stop inflammatory processes and initiate the return to the steady state. The aim of this review is to discuss how insights into the mechanism of IVIG activity may help to understand the molecular and cellular pathways underlying resolution of inflammation. We will put a special emphasis on pathways dependent on the IgG FC domain and IgG sialylation, as several recent studies have provided new insights into how this glycosylation-dependent pathway modulates innate and adaptive immune responses through different sets of C-type or I-type lectins.

Disseminated tuberculosis with severe immune thrombocytopenia

Immune thrombocytopenia is an autoimmune condition with increased platelet destruction. Immune thrombocytopenic purpura is an uncommon and rare manifestation of tuberculosis. A search of the literature available on TB-associated ITP identified only around 50 cases published between 1964 and 2016. We present an uncommon and interesting case of severe isolated immune thrombocytopenia secondary to bilateral tubercular cervical lymphadenopathy and pott's spine in 26 year old Indian male. Due to severe thrombocytopenia patient was managed with IVIg and steroids along with anti tubercular therapy. Early diagnosis and treatment with Anti tubercular therapy is important for effective control of bleeding manifestations.

Gammaplex® 5 and 10% in the treatment of primary immunodeficiency and chronic immune thrombocytopenic purpura

Immunoglobulin G is used to both prevent infection in primary immunodeficiency diseases (PIDs) and prevent bleeding in immune thrombocytopenic purpura. Gammaplex is a highly purified human intravenous immunoglobulin G available as 5 and 10% liquid formulations. Gammaplex 5% has proven efficacy and safety in PID and immune thrombocytopenic purpura, protecting against serious acute bacterial infections and treating bleeding by improving platelet counts, respectively. The therapeutic effect of Gammaplex 10% is expected to be similar to that of Gammaplex 5% based on demonstrated bioequivalence in a bridging study in PID. The availability of Gammaplex 10% provides another option to individualize therapy according to patient needs, allowing a 34% reduction in infusion time without compromising safety and tolerability.

Immune Gamma Globulin Therapeutic Indications in Immune Deficiency and Autoimmunity

Immune gamma globulin (IgG) has a long history in the treatment of both primary immune deficiency and autoimmune disorders. Disease indications continue to expand and new-generation products increase the versatility of delivery. This review encompasses a historical perspective as well as current and future implications of human immune globulin for the treatment of immune-mediated illness.

Pathogenesis and Therapeutic Mechanisms in Immune Thrombocytopenia (ITP)

Immune thrombocytopenia (ITP) is a complex autoimmune disease characterized by low platelet counts. The pathogenesis of ITP remains unclear although both antibody-mediated and/or T cell-mediated platelet destruction are key processes. In addition, impairment of T cells, cytokine imbalances, and the contribution of the bone marrow niche have now been recognized to be important. Treatment strategies are aimed at the restoration of platelet counts compatible with adequate hemostasis rather than achieving physiological platelet counts. The first line treatments focus on the inhibition of autoantibody production and platelet degradation, whereas second-line treatments include immunosuppressive drugs, such as Rituximab, and splenectomy. Finally, third-line treatments aim to stimulate platelet production by megakaryocytes. This review discusses the pathophysiology of ITP and how the different treatment modalities affect the pathogenic mechanisms.

Intravenous Immunoglobulin in the Treatment of Hematologic Disorders in Pediatrics

Intravenous immunoglobulin (IVIG) is pooled immunoglobulin G derived from human blood donors. It was introduced in the early 1980s to treat immunodeficiency disorders. Since then, its use has expanded to other fields such as neurology, rheumatology, and hematology. IVIG has been used to provide passive immunity in qualitative and quantitative immunoglobulin disorders, to neutralize antibodies in immune-mediated diseases, and as an immune modulatory agent. The difficulty of producing IVIG in high quantities, in addition to a growing list of "off-label" indications, has resulted in a worldwide shortage and increase in cost. From a pediatric hematology perspective, IVIG is considered an appropriate therapeutic option in autoimmune cytopenias, sometimes coadministrated with steroids. Its use in other hematologic disorders is questionable, and there is not sufficient evidence to recommend it. This article provides clear information to the general pediatrician about indications for IVIG therapy in children with hematologic disorders. [Pediatr Ann. 2017;46(1):e13-e18.].

Advances in Diagnosis and Treatments for Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is an acquired hemorrhagic condition characterized by the accelerated clearance of platelets caused by antiplatelet autoantibodies. A platelet count in peripheral blood <100 × 10⁹/L is the most important criterion for the diagnosis of ITP. However, the platelet count is not the sole diagnostic criterion, and the diagnosis of ITP is dependent on additional findings. ITP can be classified into three types, namely, acute, subchronic, and persistent, based on disease duration. Conventional therapy includes corticosteroids, intravenous immunoglobulin, splenectomy, and watch-and-wait. Second-line treatments for ITP include immunosuppressive therapy [eg, anti-CD20 (rituximab)], with international guidelines, including rituximab as a second-line option. The most recently licensed drugs for ITP are the thrombopoietin receptor agonists (TRAs), such as romiplostim and eltrombopag. TRAs are associated with increased platelet counts and reductions in the number of bleeding events. TRAs are usually considered safe, effective treatments for patients with chronic ITP at risk of bleeding after failure of first-line therapies. Due to the high costs of TRAs, however, it is unclear if patients prefer these agents. In addition, some new agents are under development now. This manuscript summarizes the pathophysiology, diagnosis, and treatment of ITP. The goal of all treatment strategies for ITP is to achieve a platelet count that is associated with adequate hemostasis, rather than a normal platelet count. The decision to treat should be based on the bleeding severity, bleeding risk, activity level, likely side effects of treatment, and patient preferences.

Targeting FcγRs to treat antibody-dependent autoimmunity

Self-reactive antibodies represent a significant force in autoimmune disease induction. In antibody-dependent autoimmune syndromes such as immune thrombocytopenia (ITP), systemic lupus erythematosus (SLE), myasthenia gravis and rheumatoid arthritis (RA), autoantibodies exert their inflammatory effect through FcγRs, a well-established class of cell surface receptors that interact with the Fc domain of IgG. Down-regulating FcγR functionality presents an attractive strategy to treat antibody-dependent autoimmune diseases. Various approaches, including nonspecific blocking of the IgG binding site as well as specific targeting using antagonistic monoclonal antibodies, have been explored to modulate the interaction between the Fc portion of IgG and FcγRs. The exquisite specificity and favorable pharmacokinetics of IgG make monoclonal antibodies a preferred choice. Indeed, the first antagonistic monoclonal antibody against the human FcγRIIIA had shown efficacy in refractory ITP patients; however, the practicality of using anti-FcγRIII antibody as a therapeutic was hindered by its associated adverse events, a phenomenon recapitulated in animal models. In this review, we discuss the role of FcγRs in autoimmune diseases, and focus on a novel monovalent approach to target FcγRs to resolve antibody-mediated autoimmunity.

Recent progress in understanding the pathogenesis of fetal and neonatal alloimmune thrombocytopenia

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) occurs in c. 1 in 1000 births and is caused by maternal antibodies against human platelet alloantigens that bind incompatible fetal platelets and promote their clearance from the circulation. Affected infants can experience bleeding, bruising and, in severe cases, intracranial haemorrhage and even death. As maternal screening is not routinely performed, and first pregnancies can be affected, most cases are diagnosed at delivery of a first affected pregnancy. Unlike its erythrocyte counterpart, Haemolytic Disease of the Fetus and Newborn, there is no prophylactic treatment for FNAIT. This report will review recent advances made in understanding the pathogenesis of FNAIT: the platelet alloantigens involved, maternal exposure and sensitization to fetal platelet antigens, properties of platelet Immunoglobulin G antibodies, maternal-fetal antibody transport mechanisms and efforts to develop an effective FNAIT prophylaxis.

How we use WinRho in patients with idiopathic thrombocytopenic purpura

Primary immune thrombocytopenia (ITP) is an autoimmune disease that affects children and adults. WinRho SDF is a D immune globulin product that is Food and Drug Administration approved for the treatment of ITP in D+ pediatric and adult patients. WinRho is a plasma-derived biologic product dispensed from blood banks. Transfusion medicine physicians serve as a resource to health care providers regarding blood component and derivative usage and, as such, should be familiar with the use of WinRho for ITP, including the dosage, administration, and contraindications. This report details the transfusion medicine consultation practice and guidelines at a tertiary care academic medical center for the usage of WinRho SDF in patients with ITP.

Association of autoantibody specificity and response to intravenous immunoglobulin G therapy in immune thrombocytopenia: a multicenter cohort study

BACKGROUND

Immune thrombocytopenia (ITP) is a common autoimmune bleeding disorder, in which platelet glycoprotein (GP)IIb-IIIa and GPIb-IX are the two most frequently targeted autoantigens. Our previous studies in animal models of ITP demonstrated that intravenous immunoglobulin G (IVIG) could protect against anti-GPIIb-IIIa autoantibody-mediated thrombocytopenia but failed to ameliorate ITP induced by most anti-GPIb-IX autoantibodies.

OBJECTIVES

The objective of this human study was to evaluate the association between the specificity of antiplatelet autoantibodies and response to IVIG treatment.

PATIENTS/METHODS

In this retrospective study, a cohort of 156 previously untreated adults with severe ITP who underwent IVIG therapy (0.4 g kg(-1)  day(-1) for 5 days) was analyzed. The primary outcome was response defined as platelet counts of ≥ 30 × 10(9)  L(-1) and a doubling of baseline counts within 7 days of dosing, and an absence of bleeding.

RESULTS AND CONCLUSIONS

Among the 66 patients with anti-GPIb-IX autoantibodies, only 24 (36.4%) achieved a response, as compared with 72 of 90 patients (80.0%) who were negative for anti-GPIb-IX autoantibodies (relative risk 2.2; 95% confidence interval 1.6-3.1). This study found no difference in response between patients with anti-GPIIb-IIIa autoantibodies (61.7%) and those without anti-GPIIb-IIIa autoantibodies (61.3%). Logistic regressions, including main effects and the interaction between these two autoantibodies, showed no influence of anti-GPIIb-IIIa autoantibodies on the effects of anti-GPIb-IX autoantibodies with regard to their association with IVIG response. Thus, in adults with ITP, the presence of anti-GPIb-IX autoantibodies is a predictive factor for poor response to IVIG treatment.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01666795.

RHD zygosity predicts degree of platelet response to anti-D immune globulin treatment in children with immune thrombocytopenia

Anti-D immunoglobulin is a common front-line treatment for childhood immune thrombocytopenia (ITP) that typically results in a rapid and significant increase in platelet count. Unpredictable treatment responses and interpatient variability limit more widespread use. We hypothesized that anti-D response variability is influenced by RHD gene zygosity and erythrocyte D antigen expression. We compared RHD zygosity and quantitative D antigen expression to anti-D treatment results. Hemizygous RHD subjects demonstrated significantly higher platelet increases and peak platelet counts than homozygous RHD subjects. Future studies should investigate the mechanisms by which RHD zygosity and D antigen expression affect platelet responses to anti-D immunoglobulin.

Monoclonal versus polyclonal anti-D in the treatment of ITP

Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder caused by low numbers of platelets generally due to the production of anti-platelet antibodies. One effective treatment for ITP patients who express the RhD antigen on their red blood cells has been the use of blood donor-derived pooled polyclonal anti-D. Although anti-D has served us well, it needs to be replaced with a recombinant product. While the mechanism of action of anti-D in ITP remains highly speculative, this has not thwarted attempts to replace anti-D with a monoclonal product. Although a single attempt at a monoclonal antibody was not successful in the 1990s for the treatment of ITP, more recent efforts in mouse models of ITP and ITP patients now show that monoclonal antibodies can be successful in ITP. These studies also finally help substantiate the concept that it is unlikely that contaminants in the original donor-derived preparations mediate the major ameliorative activity of anti-D in ITP.

Intravenous immunoglobulin and Alzheimer's disease: what now?

Intravenous immunoglobulin (IVIG) products are prepared from purified plasma immunoglobulins from large numbers of healthy donors. Pilot studies with the IVIG preparations Octagam and Gammagard in individuals with mild-to-moderate Alzheimer’s disease (AD) suggested stabilization of cognitive functioning in these patients, and a phase II trial with Gammagard reported similar findings. However, subsequent reports from Octagam’s phase II trial and Gammagard’s phase III trial found no evidence for slowing of AD progression. Although these recent disappointing results have reduced enthusiasm for IVIG as a possible treatment for AD, it is premature to draw final conclusions; a phase III AD trial with the IVIG product Flebogamma is still in progress. IVIG was the first attempt to use multiple antibodies to treat AD. This approach should be preferable to administration of single monoclonal antibodies in view of the multiple processes that are thought to contribute to AD neuropathology. Development of “AD-specific” preparations with higher concentrations of selected human antibodies and perhaps modified in other ways (such as increasing their anti-inflammatory effects and/or ability to cross the blood–brain barrier) should be considered. Such preparations, if generated with recombinant technology, could overcome the problems of high cost and limited supplies, which have been major concerns relating to the possible widespread use of IVIG in AD patients. This review summarizes the recent AD IVIG trials and discusses the major issues relating to possible use of IVIG for treating AD, as well as the critical questions which remain.

Intravenous immunoglobulin therapy: how does IgG modulate the immune system?

Intravenous immunoglobulin (IVIG) preparations comprise pooled IgG antibodies from the serum of thousands of donors and were initially used as an IgG replacement therapy in immunocompromised patients. Since the discovery, more than 30 years ago, that IVIG therapy can ameliorate immune thrombocytopenia, the use of IVIG preparations has been extended to a wide range of autoimmune and inflammatory diseases. Despite the broad efficacy of IVIG therapy, its modes of action remain unclear. In this Review, we cover the recent insights into the molecular and cellular pathways that are involved in IVIG-mediated immunosuppression, with a particular focus on IVIG as a therapy for IgG-dependent autoimmune diseases.

Current management of immune thrombocytopenia

Immune thrombocytopenia (ITP) is an autoimmune-mediated condition that results from antibody-mediated destruction of platelets and impaired megakaryocyte platelet production. ITP patients exhibit severe thrombocytopenia and are at risk for significant hemorrhage. Few randomized trials exist to guide management of patients with ITP. Ultimately, each patient requires an individualized treatment plan that takes into consideration the platelet count, bleeding symptoms, health-related quality of life, and medication side effects. This article provides an up-to-date review of management strategies drawing on links between the expanding amounts of clinical trial data and associated biology studies to enhance understanding of the disease heterogeneity with regard to the complex pathogenesis and response to treatment.

Clinical applications of immunoglobulin: update

Human immunoglobulin is the most used blood product in the clinical practice. Immunoglobulin applications have increased quickly since the elucidation of its immunomodulatory and antiinflammatory properties which turned this blood product into a precious tool in the treatment of numerous diseases that present with humoral immune deficiency or that cause immune system dysfunction. Currently, the approved indications for Ig are: primary immunodeficiencies, secondary immunodeficiencies (multiple myeloma or chronic lymphoid leukemia), Kawasaki syndrome, immune thrombocytopenic purpura, Guillain Barré syndrome, graft-versus-host disease following bone marrow transplantation and repeat infections in HIV children. On the other hand, there are numerous "off-label" indications of immunoglobulin, which represent 20-60% of all clinical applications of this drug. It is important to study all these indications and, above all, the scientific evidence for its use, in order to provide patients with a new therapeutic option without burdening the health system. This review results from a wide selection of papers identified in the Pubmed and Lilacs scientific electronic databases. A group of descriptors were used from human immunoglobulin to the names of each disease that immunoglobulin is clinically applied. Our main objective is to list the numerous indications of immunoglobulin, both authorized and "off-label" and to analyze these indications in the light of the most recent scientific evidence.

Platelets in inflammation and immune modulations: functions beyond hemostasis

Platelets play central roles for maintaining the homeostasis of the blood coagulation. As they are also involved in immune responses and host defenses, increasing evidences have suggested that platelets exert other roles beyond their well-recognized function in preventing bleeding. This review is focused on inflammation, allergy and immune modulations of platelets. Platelets conduct immunoregulation through secretion of functional mediators, interaction with various immune cells, endothelial cells and beneficial for the leukocyte infiltration to inflamed/allergic tissues. In these regulations, the leukocytes are influenced by and receiving the signals from platelets. In contrast, rare attentions were focused on platelet regulations by immune system. An intriguingly example in the intravenous immunoglobulin (IVIg) treatment is discussed, in which dendritic cells exert anti-inflammatory effect through platelets. This further suggests that coagulant and immune systems are tightly associated rather than separate entities. The cross-talks between these two systems implicate that platelet therapy may have application beyond thrombosis, and immune interventions may have potentials to treat thrombosis diseases.

Management of children and adolescents with primary immune thrombocytopenia: controversies and solutions

The management including diagnostic procedures, prophylaxis, treatment and follow-up of patients with primary immune thrombocytopenia (ITP) in childhood is controversial due to limited clinical data, difficulties in the estimation of individual bleeding risk and heterogeneity of pathophysiology potentially causing various treatment responses. Advances in the management of children include increased international collaborations, improved quality of diagnosis and treatment, increased clinical data, refinement of consensus statements where clinical evidence is absent, new drugs and last but not least establishment of watch-and-wait strategies. The Intercontinental Cooperative ITP Study Group promotes international collaboration since more than 10 years based on a worldwide network and experience in registries. Future considerations include concentration of available resources, strengthening international collaboration, focusing on most important scientific and clinical questions, such as identification of the subgroup of patients that benefits most from prophylactic platelet-enhancing treatments and investigation of treatment endpoints other than concepts solely based on the platelet count, including bleeding symptoms, health-related quality of life and economical aspects of treatments.

The neonatal Fc receptor (FcRn) is not required for IVIg or anti-CD44 monoclonal antibody–mediated amelioration of murine immune thrombocytopenia

To definitively determine whether the neonatal Fc receptor (FcRn) is required for the acute amelioration of immune thrombocytopenia (ITP) by IVIg, we used FcRn-deficient mice in a murine ITP model. Mice injected with antiplatelet antibody in the presence or absence of IVIg displayed no difference in platelet-associated IgG between FcRn deficient versus C57BL/6 mice. FcRn-deficient mice treated with high-dose (2 g/kg) IVIg or a low–dose (2 mg/kg) of an IVIg-mimetic CD44 antibody were, however, protected from thrombocytopenia to an equivalent extent as wild-type mice. To verify and substantiate the results found with FcRn-deficient mice, we used β2-microglobulin–deficient mice (which do not express functional FcRn) and found that IVIg or CD44 antibody also protected them from thrombocytopenia. These data suggest that for both high-dose IVIg as well as low-dose CD44 antibody treatment in an acute ITP model, FcRn expression is neither necessary nor required.

Apoptosis in the anucleate platelet

For many years, programmed cell death, known as apoptosis, was attributed exclusively to nucleated cells. Currently, however, apoptosis is also well-documented in anucleate platelets. This review describes extrinsic and intrinsic pathways of apoptosis in nucleated cells and in platelets, platelet apoptosis induced by multiple chemical stimuli and shear stresses, markers of platelet apoptosis, mitochodrial control of platelet apoptosis, and apoptosis mediated by platelet surface receptors PAR-1, GPIIbIIIa and GPIbα. In addition, this review presents data on platelet apoptosis provoked by aging of platelets in vitro during platelet storage, platelet apoptosis in pathological settings in humans and animal models, and inhibition of platelet apoptosis by cyclosporin A, intravenous immunoglobulin and GPIIbIIIa antagonist drugs.

RhIG for the treatment of immune thrombocytopenia: consensus and controversy (CME)

Anti-D immune globulin (RhIG) is a front-line option in North America for the treatment of immune thrombocytopenia (ITP) in children and adults. Recently, addition of a Food and Drug Administration-mandated black box warning highlighted the risks of intravascular hemolysis, renal failure, and disseminated intravascular coagulation after anti-D infusion, prompting concern within the medical community regarding its use. A working group convened in response to this warning to prepare a consensus document regarding the safety of RhIG because there has been no increased incidence of adverse events since the initial discovery of these reactions many years ago. The efficacy of anti-D is well documented and only briefly reviewed. The estimated incidence and proposed mechanisms for the rare, major treatment-related complications are discussed, and signal detection data associated with heightened risk of acute hemolytic reactions are presented. The importance of considering host factors, given the rarity of severe reactions, is emphasized. Safety profiles of parallel treatment options are reviewed. The working group consensus is that RhIG has comparable safety and efficacy to other front-line agents for the treatment of children and adults with ITP. Safety may be further improved by careful patient selection.

Delayed hemolytic transfusion reaction in children with sickle cell disease

BACKGROUND

Transfusion is a cornerstone of the management of sickle cell disease but carries a high risk of hemolytic transfusion reaction, probably because of differences in erythrocyte antigens between blood donors of European descent and patients of African descent. Patients may experience hemolytic transfusion reactions that are delayed by from a few days to two weeks and manifest as acute hemolysis (hemoglobinuria, jaundice, and pallor), symptoms suggesting severe vaso-occlusive crisis (pain, fever, and acute chest syndrome), and profound anemia, often with reticulocytopenia. This case-series study aims to describe the main characteristics of this syndrome, to discuss its pathophysiology, and to propose a management strategy.

DESIGN AND METHODS

We identified 8 pediatric cases of delayed hemolytic transfusion reactions between 2006 and 2009 in the database of the Necker Hospital, France. All patients had received cross-matched red cell units compatible in the ABO, RH, and KEL systems. We reviewed the medical charts in the computerized blood transfusion databases. All patients were admitted to the intensive care unit. We progressively adopted the following strategy: intravenous immunoglobulins, and darbopoietin alpha when the reticulocyte count was below 150×10(9)/L, without further blood transfusion during the acute episode unless absolutely necessary.

RESULTS

The median time between the transfusion and the diagnosis of delayed hemolytic transfusion reaction was six days. All patients had severe bone pain; all but one had a high-grade fever. Five patients had hemoglobin levels less than than 4 g/dL and 3 had reticulocytopenia. In 5 patients, no new antibody was found; one patient had weakly reactive antibodies. Only 2 patients had new allo-antibodies possibly responsible for the delayed hemolytic reaction.

CONCLUSIONS

The initial symptoms of delayed hemolytic transfusion reaction were complex and mimicked other complications of sickle cell disease. In most of our cases, no new antibody was identified, which underlines the complexity of the pathophysiology of this syndrome.

FNAIT: the fetus pleads guilty!

Fetal/neonatal alloimmune thrombocytopenia (FNAIT) resulting from fetal platelet destruction by maternal alloantibodies is the most common cause of severe fetal thrombocytopenia and of neonatal thrombocytopenia in maternity wards. The pathophysiology is largely unknown. The fetus has long been considered as an "innocent bystander."

Dendritic cells modulate platelet activity in IVIg-mediated amelioration of ITP in mice

Intravenous immunoglobulin (IVIg) is an effective treatment against immune thrombocytopenia (ITP). Previous studies suggested that IVIg exerts this ameliorative role through 2 different leukocyte subsets. Dendritic cells (DCs) modulate the immunosuppression in an adoptive cell transfer model, and phagocytes up-regulate their inhibitory IgG Fc receptors (FcγR)IIB expression and thereby ameliorate the inflammatory response and platelet clearance. However, whether or not regulatory mechanisms exist among DCs, phagocytes, and platelets is still largely unknown. In this study we present findings that IVIg-primed splenic CD11c+ DCs (IVIg-DCs) primarily mediate their anti-inflammatory effects at the level of the platelet rather than the phagocyte. IVIg-DCs did not ameliorate ITP in Fcgr2b−/−, Fcgr3−/−, nor P-Selp−/− mice, implicating the potential involvement of these pathways in IVIg action. As platelets are a component of DC regulatory circuits, these findings may suggest an alternative perspective for the use of IVIg treatment.

Effect of immunoglobulin G (IgG) interchain disulfide bond cleavage on efficacy of intravenous immunoglobulin for immune thrombocytopenic purpura (ITP)

Intravenous immunoglobulin (IVIG) has been used widely to treat immune thrombocytopenic purpura (ITP), but the mechanisms of its action remain unclear. We investigated the affinity for Fcγ receptors (FcγRs) and the thrombocytopenia-ameliorating effect of S-sulfonated gammaglobulin (SGG) and S-alkylated gammaglobulin (AGG), in comparison with unmodified gammaglobulin (GG), in a mouse ITP model. Cleavage of immunoglobulin (Ig)G interchain disulfide bonds by either S-sulfonation or S-alkylation did not decrease the affinity for FcγRIIA (CD32A) and FcγRIIB (CD32B), but did decrease the affinity for FcγRIA (CD64A) and FcγRIIIA (CD16A), presumably because of changes in H-chain configuration. The interchain disulfide bond cleavage decreased the affinity much more for mouse FcγRIV than for mouse FcγRIIB. The ability of AGG to ameliorate ITP was greatly diminished, while SGG, whose disulfide bonds are reconstituted in vivo, was as effective as GG. These results suggest that the interchain disulfide bonds are important for therapeutic effect. It is also suggested that the interaction of IVIG with the inhibitory receptor FcγRIIB is insufficient for effective amelioration of ITP and that, at least in this model, direct binding of IVIG to FcγRIIIA is also required.

Mechanisms of action of intravenous immunoglobulins

Intravenous immunoglobulin (IVIg) has been used for nearly three decades as an efficient anti-inflammatory therapeutic regimen in a growing number of autoimmune diseases. Despite this their success in clinical application, the mechanism of action of IVIg therapy remains elusive. During the last few years, several mechanisms dependent on either the IgG variable or constant fragment have been proposed to explain the potent immunomodulatory activity of IVIg. This review will discuss which molecular and cellular pathways might be involved in the anti-inflammatory activity of IVIg and for which types of autoimmune diseases they might be relevant.

Animal models of immune thrombocytopenia (ITP)

With regards to research animal models related to immune thrombocytopenia (ITP), there is an extensive literature of over 300 publications published since 1959. It appears that many of these models either confirm what has been found in human ITP or, in some instances, are the first to describe a phenomenon related to ITP that is still of relevance today in human medicine. These models will undoubtedly play a significant role in the future research of human ITP particularly related to understanding of the pathogenesis of the disorder and the development of novel therapeutics. This review will highlight some of the major animal models utilized for ITP research and will present a somewhat historical aspect of the subject.