A new concept for the effector mechanism of intravenous immunoglobulin in hemocytopenias

Neutropenias following allogeneic bone marrow transplantation: response to therapy with high-dose intravenous immunoglobulin

Cytopenias following bone marrow transplantation may be severe and life-threatening. These have been described post-allogeneic Klumpp, 1991: Bone Marrow Transplant 8:159-171. or post-autologous bone marrow transplants Khouri et al., 1994: J Clin Oncol 12:748-758. as well as with peripheral blood stem cell transplantation Klumpp et al., 1992: Am J Hematol 41:215-217. It can be immune mediated, associated on occasions with graft-versus-host disease (GVHD) Anasetti et al., 1989: Blood 4:1054-1058; however, in most cases, the underlying mechanism is uncertain. The treatment of post-transplant cytopenias is not well established, and they are often refractory to immunosuppressive therapy with steroids. Herein we describe two cases of neutropenia after allogeneic bone marrow transplantation that improved after therapy with high-dose intravenous immunoglobulin.

IVIG in the treatment of children with acute and chronic idiopathic thrombocytopenic purpura and the autoimmune cytopenias

IVIG has been shown to be useful in the treatment of acute and chronic ITP, immune neutropenia, and in some cases of AIHA. The mechanism of action of IVIG is owing to a number of factors, which include Fc blockade, immune modulation of T- and B-cell number and function, alterations in NK activity, and direct effects on autoantibody binding and production via the antiidiotypic antibody network. Current research efforts are directed toward elucidation of these modalities and determination of their relative importance in treating patients with immune-mediated cytopenias.

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 for the treatment of autoimmune neutropenia of childhood and autoimmune hemolytic anemia

Intravenous gamma globulin (IVIG) was used to treat autoimmune neutropenia of childhood and autoimmune hemolytic anemia, two autoimmune disorders not previously treated with this modality. Six children younger than two years of age, who presented with severe infections and persistent absolute neutrophil counts (300/mm3), were treated with 1 g of gamma globulin per kilo body weight until counts reached more than 1,000/mm3. The average response occurred with a dose of 3.0 g/kg within five to seven days and lasted an average of 14 days before counts decreased to baseline levels. Four patients with autoimmune hemolytic anemia were also treated with IVIG, 1 g/kg for five to seven days (average dose of 5 g/kg), for severe Coombs'-positive hemolytic anemia. Response of the hemolytic anemia to IVIG was excellent in one patient and good in two patients. No response occurred in the fourth patient. Response was slower in these patients than in patients treated for immune thrombocytopenic purpura (ITP). The average total amount of gamma globulin required for a response is markedly different: 1 g/kg for ITP, 3.0 g/kg for autoimmune neutropenia, and 5 g/kg for hemolytic anemia. Possible mechanisms of action include blockade of reticuloendothelial system Fc receptors, suppression of autoantibody production, and/or interference in the binding of autoantibodies to target cells.

Binding and antibody blocking effects of intravenous IgG preparation on peripheral blood cells

The mode of action of high dose intravenous gammaglobulin (IVGG) in idiopathic thrombocytopenic purpura (ITP) is controversial. This study used immunofluorescence techniques to investigate the possibility that IVGG binds to peripheral blood cells and that such binding blocks attachment of cell specific autoantibodies. IVGG bound to platelets, neutrophils, monocytes and lymphocytes. Erythrocytes appeared to bind only anti-A and anti-B present in the IVGG. Multimeric and monomeric fractions of IVGG also bound to these cells. However, F(ab')2 fragments of the IVGG reacted only weakly with platelets, neutrophils, monocytes and lymphocytes. Binding of IVGG to platelets and neutrophils did not prevent opsonization of these cells by monoclonal antibodies with specificities corresponding to those previously ascribed to platelet and neutrophil autoantibodies. This suggests that IVGG does not act by blocking attachment of autoantibodies to platelets in ITP.

Red cell sequestration during high dose intravenous immunoglobulin in idiopathic thrombocytopenic purpura

The cellular interactions involved in the platelet response after immunoglobulin infusion in acute and chronic idiopathic thrombocytopenic purpura (ITP) are unknown. There have been a number of theories including the competitive inhibition of platelet-binding to macrophages by the preferential sequestration of immunoglobulin coated red cells. We report a study to examine this hypothesis. Adult acute and chronic patients were given infusions of immunoglobulin at a rate of 0.4 g/kg body weight, daily for 5 days. Serum haptoglobin, lactate dehydrogenase and the absolute reticulocyte counts were monitored and no significant change in any value was seen during the period of study. A red cell survival was performed on four of the patients and no increase in the rate of red cell clearance occurred during the infusion period. We conclude from this that in these patients no significant degree of haemolysis was provoked by the infusion although this does not preclude this as a mechanism of action in some individuals.

Specific and nonspecific mechanisms of action of immunoglobulin G in therapy of idiopathic thrombocytopenic purpura (ITP)

The efficacy of IgG infusion therapy in ITP is now established even in cases resistant to other forms of therapy. However, the mechanism of action is still speculative. We assume that a correction of the elevated thrombocyte clearance is brought about at several levels. First, antibodies specific for an inciting antigen (and for which the patient is deficient) may remove free antigen and/or immune complexes which adhere to platelet surfaces, thereby rendering platelets less susceptible to clearance. Second, IgG may act nonspecifically by protecting the platelet surface from becoming covered with immune complexes. Third, monomeric IgG may display a nonspecific inhibitory effect at the level of the interaction of immunologically altered platelets with Fc receptors of mononuclear phagocytes. For the latter effect, good in vivo evidence exists. However, it must be born in mind that interaction of antibodies with Fc receptors is but one mechanisms for triggering adherence and endocytosis. A variety of other receptors and binding sites exists which may interact with immunologically altered thrombocytes. These may either trigger phagocytes on their own or facilitate the interaction of antibodies and Fc receptors. How IgG infusion influences such interactions remains to be determined.