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Biomedical subjects

Seng Song

Publications and source records attributed to Seng Song.

9 recordsLinked to original sources
PubMed2006

Mechanisms of action of intravenous immunoglobulin in the treatment of immune thrombocytopenia.

Intravenous immunoglobulin (IVIG) is currently used to treat a multitude of autoimmune disorders including immune thrombocytopenic purpura (ITP), yet the mechanism of action of IVIG remains unresolved. Using a murine model of ITP in which IVIG functions therapeutically, our laboratory has addressed such theories as blockade/inhibition of the mononuclear phagocytic system, cytokine regulation, and neutralization of pathogenic autoantibodies mediated by anti-idiotypic antibodies, and these findings will be discussed herein. We have also demonstrated that soluble immune complexes can completely recapitulate the therapeutic effects of IVIG in ITP, and recent work from us has identified activating Fcgamma receptors on CD11c+ dendritic cells as the relevant molecular target of IVIG in the acute resolution of murine immune thrombocytopenia. This and other work to devise antibody-based IVIG alternative therapies will also be addressed.

Animals↗
PubMed2006

A role for IL-1 receptor antagonist or other cytokines in the acute therapeutic effects of IVIg?

The exact mechanism of action of IVIg in the amelioration of immune thrombocytopenic purpura (ITP) is still unclear. Studies have suggested that IVIg may function through the regulation of cytokines, including interleukin-1 receptor antagonist (IL-1Ra), an inhibitor of phagocytosis. Using a mouse model relevant to ITP, we confirm an increase in mouse serum levels of IL-1Ra after exposure to IVIg, yet a recombinant IL-1Ra did not ameliorate thrombocytopenia. IVIg has also been shown to affect the expression of other regulatory cytokines. We have also recently established that IVIg specifically targets activating FcgammaRs on CD11c+ dendritic cells (DCs) as its primary mechanism of action in the amelioration of murine ITP. Herein, we show that IVIg functions therapeutically in mice lacking specific cytokines or their receptors that can potentially affect DC/macrophage function (IL-1 receptor, IL-4, IL-10, IL-12beta, TNF-alpha, IFN-gamma receptor, MIP-1alpha). This suggests that while IVIg may mediate the release of a variety of cytokines, the cytokines tested do not directly participate in the mechanism of IVIg action.

Animals↗
PubMed2006

Intravenous immunoglobulin ameliorates ITP via activating Fc gamma receptors on dendritic cells.

Despite a more than 20-year experience of therapeutic benefit, the relevant molecular and cellular targets of intravenous immunoglobulin (IVIg) in autoimmune disease remain unclear. Contrary to the prevailing theories of IVIg action in autoimmunity, we show that IVIg drives signaling through activating Fc gamma receptors (Fc gammaR) in the amelioration of mouse immune thrombocytopenic purpura (ITP). The actual administration of IVIg was unnecessary because as few as 10(5) IVIg-treated cells could, upon adoptive transfer, ameliorate ITP. IVIg did not interact with the inhibitory Fc gammaRIIB on the initiator cell, although Fc gammaRIIB does have a role in the late phase of IVIg action. Notably, only IVIg-treated CD11c+ dendritic cells could mediate these effects. We hypothesize that IVIg forms soluble immune complexes in vivo that prime dendritic-cell regulatory activity. In conclusion, the clinical effects of IVIg in ameliorating ITP seem to involve the acute interaction of IVIg with activating Fc gammaR on dendritic cells.

Adoptive Transfer↗
PubMed2005

Can antibodies with specificity for soluble antigens mimic the therapeutic effects of intravenous IgG in the treatment of autoimmune disease?

Intravenous Ig (IVIg) mediates protection from the effects of immune thrombocytopenic purpura (ITP) as well as numerous other autoimmune states; however, the active antibodies within IVIg are unknown. There is some evidence that antibodies specific for a cell-associated antigen on erythrocytes are responsible, at least in part, for the therapeutic effect of IVIg in ITP. Yet whether an IVIg directed to a soluble antigen can likewise be beneficial in ITP or other autoimmune diseases is also unknown. A murine model of ITP was used to determine the effectiveness of IgG specific to soluble antigens in treating immune thrombocytopenic purpura. Mice experimentally treated with soluble OVA + anti-OVA versus mice treated with OVA conjugated to rbcs (OVA-rbcs) + anti-OVA were compared. In both situations, mice were protected from ITP. Both these experimental therapeutic regimes acted in a complement-independent fashion and both also blocked reticuloendothelial function. In contrast to OVA-rbcs + anti-OVA, soluble OVA + anti-OVA (as well as IVIg) did not have any effect on thrombocytopenia in mice lacking the inhibitory receptor FcgammaRIIB (FcgammaRIIB(-/-) mice). Similarly, antibodies reactive with the endogenous soluble antigens albumin and transferrin also ameliorated ITP in an FcgammaRIIB-dependent manner. Finally, broadening the significance of these experiments was the finding that anti-albumin was protective in a K/BxN serum-induced arthritis model. We conclude that IgG antibodies directed to soluble antigens ameliorated 2 disparate IVIg-treatable autoimmune diseases.

Animals↗
PubMed2004

Monoclonal antibodies that mimic the action of anti-D in the amelioration of murine ITP act by a mechanism distinct from that of IVIg.

The mechanism of action of intravenous immunoglobulin (IVIg) and polyclonal anti-D-mediated reversal of immune thrombocytopenia (ITP) is still unclear. However, in a murine model of ITP, the therapeutic effect of IVIg appears to be wholly dependent upon the expression of the inhibitory Fc receptor, Fc gamma RIIB. We previously demonstrated that, similar to anti-D in humans, 2 erythrocyte-reactive monoclonal antibodies (TER119 and M1/69) ameliorated murine ITP and inhibited reticuloendothelial system (RES) function at doses that protected against thrombocytopenia. The current study evaluated the involvement of the inhibitory and activating Fc receptors, Fc gamma RIIB and Fc gamma RIIIA, respectively, in the TER119 and M1/69-mediated inhibition of thrombocytopenia. In contrast to IVIg, in Fc gamma RIIB-deficient mice, both monoclonal antibodies ameliorated ITP and both significantly down-regulated the level of expression of the activating Fc gamma RIIIA in splenic macrophages. These results indicate that anti-erythrocyte antibodies that ameliorate ITP act independently of Fc gamma RIIB expression but are dependent upon the activating Fc gamma RIIIA.

Animals↗
PubMed2003

IVIg-mediated amelioration of murine ITP via FcgammaRIIB is independent of SHIP1, SHP-1, and Btk activity.

It has been established that amelioration of murine immune thrombocytopenia purpura (ITP) by IVIg is dependent on the inhibitory receptor FcgammaRIIB. Co-cross-linking of the FcgammaRIIB with the B-cell receptor complex or with FcepsilonRI in mast cells results in cell inhibition, which is mediated by recruitment of the inositol phosphatase SHIP1 to the cytoplasmic tail of the FcgammaR. The FcgammaRIIB can also associate with protein tyrosine phosphatase SHP-1 as a potential secondary target of the receptor. Alternatively, homoaggregation of FcgammaRIIB can induce a proapoptotic state in B cells that is dependent on the presence of Bruton tyrosine kinase (Btk), a kinase also expressed in monocytes. We sought to determine if these signaling pathways may direct IVIg-mediated FcgammaRIIB-dependent regulation of in vivo monocyte function in a murine model of ITP in which IVIg functions in an FcgammaRIIB-dependent manner. We demonstrate that mice deficient in SHIP1, SHP-1, and Btk respond to the ameliorating effects of IVIg with the same kinetics as control mice. We conclude that IVIgmediated inhibitory pathways operating via monocyte FcgammaRIIB may involve a transmembrane signaling pathway different from that of B cells.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed2003

Understanding platelet function through signal transduction.

Platelets are activated by a number of stimuli resulting in the expression and/or activation of surface receptors, secretion of vasoactive substances, adhesion, aggregation, and finally thrombus formation. These events are propagated by a process known as transmembrane signaling, which relays the activating signal from the platelet membrane (eg, von Willebrand Factor binding to glycoprotein Ib) to the inside of the platelet which then serves to activate the platelet via a cascade of biochemical interactions. Inhibition of these transmembrane signaling molecules with a variety of available inhibitors or antagonists can in many cases prevent the platelet from becoming activated. An awareness of the mechanisms involved in platelet transmembrane signaling and the recent availability of new reagents to inhibit signaling may provide us with additional means to prevent platelet activation and perhaps even ameliorate the platelet storage lesion. This review will provide an introduction to the field of platelet transmembrane signaling and give an overview of some of the platelet signaling mechanisms that are relevant to transfusion medicine.

Blood Platelets↗
PubMed2002

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.

Animals↗