Prolongation of Platelet Survival in Idiopathic Thrombocytopenic Purpura by High-Dose Intravenous Gamma Globulin

Mechanism of action of IVIG and anti-D in ITP

Infusion of large amounts of intravenous immunoglobulin (IVIG) or polyclonal anti-D can reverse thrombocytopenia in patients with idiopathic thrombocytopenic purpura within hours of the administration of these products. It has been suggested that the effects of IVIG appear to far outlast several half-lives of the product. Several mechanisms have been proposed to explain both the acute and long term effects of IVIG. These will be discussed in this review.

Monoclonal IgG can ameliorate immune thrombocytopenia in a murine model of ITP: an alternative to IVIG

Intravenous immunoglobulin (IVIG) is used to treat immune thrombocytopenia resulting from a variety of autoimmune and nonautoimmune diseases such as idiopathic thrombocytopenic purpura (ITP), heparin-induced thrombocytopenia, and posttransfusion purpura. IVIG is a limited resource and although considered safe, may nevertheless carry some risk of transferring disease. Its high cost makes monoclonal antibodies, capable of mimicking the clinical effects of IVIG, highly desirable. We show here, using a murine model of ITP, that selected monoclonal antibodies can protect against thrombocytopenia. SCID mice were pretreated with 1 of 21 monoclonal antibodies before induction of thrombocytopenia by antiplatelet antibody. Four antibodies reacted with the CD24 antigen on erythrocytes. Two antibodies were of the IgM class, and although one IgM antibody caused a minimal degree of anemia (P <.05), neither antibody ameliorated immune thrombocytopenia. One of 2 anti-CD24 antibodies of the IgG class ameliorated immune thrombocytopenia and blocked reticuloendothelial system function at the same doses that protected against thrombocytopenia. Some antibodies reactive with other circulating cell types also protected against immune-mediated thrombocytopenia while no antibody without a distinct target antigen in the mice was protective. Protective monoclonal antibodies significantly prevented thrombocytopenia at down to a 1000-fold lower dose (200 microg/kg) as compared with standard IVIG treatment (2 g/kg). It is concluded that monoclonal IgG with specificity for a circulating cellular target antigen may provide an alternative therapeutic approach to treating immune thrombocytopenia.

Mechanism of action of IVIG in ITP

IVIG is prepared from large pools of plasma from healthy donors and the IgG is present predominantly in monomeric form. It was first reported in 1981 by Dr. Paul Imbach that high doses of IVIG promote fast recovery of ITP in children. Despite extensive clinical use in a variety of autoimmune and inflammatory states, the mechanism of action of IVIG remains as yet incompletely understood. Several theories have been proposed to explain how administration of IVIG to individuals with ITP increases the platelet count. Following is an overview of some of the major theories.

Intravenous immunoglobulin and anti-D in idiopathic thrombocytopenic purpura (ITP): mechanisms of action

Infusion of large amounts of intravenous immunoglobulin (IVIG) or anti-D can reverse the low platelet count in patients with ITP within hours of the initiation of treatment. In some cases, the effects of IVIG appear to far outlast several half-lives of the product. Several mechanisms have been proposed to explain these rapid and long term effects and these will be discussed in this review.

Use of intravenous immune globulin therapy: an overview

The intravenous immune globulin (IGIV) preparations are reviewed with respect to method of preparation, pharmacokinetics, clinical uses (with emphasis on the labeled indications), and adverse reactions; a brief review of the immune system also is provided. IGIV preparations are approved for the treatment of hypogammaglobulinemia, recurrent bacterial infections due to B-cell chronic lymphocytic leukemia, and idiopathic thrombocytopenic purpura (ITP). The mechanism of action in the first two indications is passive replacement of antibodies, but in ITP the mechanism is not clearly established. The clinical literature on the use of IGIV for these indications is summarized. In patients with ITP, platelet counts return to safe levels and the number of infections is reduced in patients with primary humoral immunodeficiency treated with IGIV. The use of IGIV in pregnant women and premature infants is controversial. Adverse reactions are primarily related to infusion rate, activation of complement, and anaphylactic reactions to a component of the product. There is minimal to no risk of viral transmission with IGIV therapy. IGIV also has been administered safely on an outpatient or homecare basis. This has led to a feeling of greater control by patients over their chronic illness. Other uses of IGIV are under investigation. As our understanding of the immune system and the pharmacology of immune globulin increases, the uses of IGIV will expand.

Idiopathic thrombocytopenic purpura (ITP): immunomodulation by intravenous immunoglobulin (IVIg)

ITP is a destructive thrombocytopenia. Platelets are coated with antibodies and these opsonized platelets are rapidly removed by phagocytes. On the other hand, therapeutic application of antibody concentrates (IVIg) rapidly raise platelet counts, and in some patients, sustained platelet recovery has been observed. The mechanism of action of IVIg is far from being clear. Several possible mechanism of action of IVIg treatment have been described. The immediate effect of IVIg seems to be a decrease in (unspecific) Fc mediated mononuclear phagocytosis, the long term effect might be a change in the complex network of the regulatory function of the immune response. Both types of interactions seem to play a keyrole in the immunomodulation. The various possible modes of actions evoke investigation of IVIg in a wide range of diseases with similar ineffective immune response. Controlled clinical studies have to be done to prove or disapprove the use of IVIg in other indications.

Use of intravenous gamma globulin in children and adolescents with idiopathic thrombocytopenic purpura and other immune thrombocytopenias

Approximately 85 to 90 percent of cases of idiopathic thrombocytopenic purpura (ITP) in children are of the acute, self-limited variety that generally occurs after a viral infection. The remaining 10 to 15 percent of children with this disorder have the chronic (autoimmune) type of ITP. For these patients, splenectomy is often the recommended treatment if severe bleeding occurs and platelet counts remain below 40,000/mm3. However, splenectomy has associated risks and the response to this surgery cannot always be predicted. Intravenous gamma globulin (IVIG) has proven useful as an alternative to splenectomy, especially in children who are considered too young for splenectomy or in those in whom there is no response to splenectomy. It should be noted that booster shots are frequently required and the patient's ITP may become refractory. IVIG may also be useful in preparing a child with ITP for splenectomy and in treating children or adolescents with ITP who have central nervous system or other serious hemorrhages. Although IVIG is not always effective in raising the platelet count, it does provide a very useful alternative method of treating this disorder.

Intravenous gammaglobulin (Gaminume) for treatment of chronic idiopathic thrombocytopenic purpura (ITP): a two-year follow-up

Thirteen subjects 5-20 years of age with the chronic, autoimmune form of idiopathic thrombocytopenic purpura (ITP) were given intravenous gammaglobulin (Gamimune; Cutter Biological, Berkeley, CA) in a dose of 400 mg/kg per day for 5 consecutive days. Two of the 13 children had undergone splenectomy; the other 11 had not. Eight of these 13 children had also received corticosteroid therapy with no sustained increase in platelet counts. Six of 13 children had a good or excellent response to the first 5 day course of gammaglobulin therapy, and one had a fair response. The peak platelet count occurred within 7 days of the start of therapy except in one patient, whose platelet count peaked on day 12. Six of seven patients who initially responded to Gamimune required booster doses to maintain platelet counts at a safe level. All children had marked increases in serum IgG following Gamimune except one (who had undergone splenectomy for chronic ITP), who had high baseline levels of immunoglobulin G (IgG). No untoward reactions necessitating cessation of therapy were encountered during this study. The most common side effect observed was headache. During the first year of follow-up after Gamimune, three of seven initial responders became refractory to Gamimune therapy. Two of these three refractory subjects later underwent splenectomy with excellent response. The third refractory patient who was splenectomized prior to gammaglobulin therapy had spontaneous remission of his ITP 5 months after the last dose of Gamimune. Three of the four other initial responders have continued to do well and have maintained platelet counts above 40,000/mm3 (one without booster). The fourth subject dropped out of the study. Thus our observations indicate that Gamimune is an effective form of treatment for some children with chronic ITP, and can be considered as an alternative to splenectomy or as a potential therapeutic modality in those who have failed to respond to splenectomy.

Lack of efficacy of high-dose intravenous immunoglobulin in autoimmune haemolytic anaemia: a clue to its mechanism

5 patients with autoimmune haemolytic anaemia (AIHA) of warm type (4 idiopathic, 1 associated with systemic lupus erythematosus and thrombocytopenia) were treated with high doses of i.v. immunoglobulin (IgG; Sandoglobulin; 2.0 g/kg body weight). IgG therapy was ineffective in all 5 cases as indicated by a lack of clinical improvement, continuous signs of accelerated red blood cell (RBC) destruction, and an unchanged survival rate of 51Cr-labelled autologous RBC in 4 patients studied. IgG infused at equivalent doses into 5 healthy volunteers led to an increase of IgG coating of autologous RBC (irrespective of the ABO blood groups) without concomitant changes of haemoglobin, haematocrit or reticulocytes, increase of serum IgM in 3/5, a decrease of serum C4 in 5/5, and a decrease of serum haptoglobin in 2/5 individuals. We conclude that IgG at a dose of 2.0 g/kg body weight is ineffective in AIHA. This may be caused by an increased, though clinically inapparent, interaction of IgG-coated autologous RBC with the mononuclear phagocyte system.