Complement-Independent, Peroxide-Induced Antibody Lysis of Platelets in HIV-1-Related Immune Thrombocytopenia

Abstract

Immunologic thrombocytopenia is seen commonly in HIV-1 infection. The pathogenesis of this problem has been unclear, but it is associated with circulating immune complexes that contain platelet membrane components and anti-platelet membrane GPIIIa49-66 IgG antibodies. These antibodies cause acute thrombocytopenia when injected into mice. We now show that purified anti-GPIIIa49-66 causes platelet fragmentation, in vitro in the absence of complement, and in vivo in wild-type and C3-deficient mice. The mechanism of complement-independent platelet lysis is shown to be caused by the antibody-induced generation of H202, as indicated by in vitro experiments with inhibitors of reactive oxygen species, and in vivo studies carried out with p47phox-deficient mice. Thus, a novel mechanism of immunologic platelet clearance is described in which an anti-platelet IgG causes platelet fragmentation via the induction of reactive oxygen species.

C-reactive protein enhances IgG-mediated phagocyte responses and thrombocytopenia

“…30,35,36 This suggests this effect to be a general feature of antibodies targeting GPIIIa-perhaps the GPIIb/IIIa complex-as we now also report CRP also amplify platelet removal by rat-anti-mouse GPIIb. Importantly, this still needs to be investigated in detail using a panel of antiplatelet antibodies against various GPIIb/IIIa epitopes, ITP sera containing various combinations of antibodies, and against other platelet proteins.…”

“…34 That anti-HPA-1a antibodies induce platelet oxidation is in agreement with studies showing that anti-GPIIIa antibodies, the glycoprotein expressing the HPA-1a epitope, also induce cellular activation through oxidative damage initiated by the platelet NADPH oxidase. 30,35,36 This suggests this effect to be a general feature of antibodies targeting GPIIIa-perhaps the GPIIb/IIIa complex-as we now also report CRP also amplify platelet removal by rat-anti-mouse GPIIb. Importantly, this still needs to be investigated in detail using a panel of antiplatelet antibodies against various GPIIb/IIIa epitopes, ITP sera containing various combinations of antibodies, and against other platelet proteins.…”

“…As oxidized low-density lipoprotein (LDL) particles and apoptotic cells have been shown to expose phosphatidylcholine residues, 28,29 and because anti-GPIIIa (containing the HPA-1a epitope, the target of the FNAIT sera and of the B2G1 antibody used in this study) antibodies have been shown to induce oxidation of platelets, 30 we investigated whether platelet oxidation contributed to CRP binding. Pretreatment of platelets with diphenylene iodonium (DPI), an inhibitor of various sources of oxygen radical including NADPH oxidase, 31 resulted in less binding of opsonized platelets to CRP compared with untreated opsonized platelets ( Figure 4E).…”

Anticorps catalytiques ou abzymes

“…Cette observation étaye cependant l'hypothèse d'un rôle protecteur intrinsèque des anticorps dans les conditions physiologiques, rôle indépen-dant de leur capacité de neutraliser les antigènes étrangers, de faciliter leur endocytose par les cellules présenta-trices de l'antigène et de permettre leur élimination. Toutefois, la production d'H 2 O 2 qu'induisent les IgG anti-GPIIIa (glycoprotéine plaquettaire équivalente de la chaîne β3 des intégrines et qui s'associe à la GPIIb pour former un complexe essentiel à l'activation plaquettaire), qui surviennent au cours de l'infection par le VIH, a été incriminée dans l'induction par ces anticorps d'une thrombocytopénie [26].…”

A Humanized Single-Chain Variable Fragment Antibody Against Beta3 Integrin in Escherichia coli

“…This antibody induces complementindependent platelet oxidative fragmentation and death by generation of reactive oxygen species through the activation of 12-lipoxygenase and NADPH oxidase. (1,2) The development of this Ab in HIV-1-ITP patients results from the molecular mimicry of epitopes on the polymorphic regions of HIV or HCV protein. (3,4) By screening a human phage display library with the GPIIIa49-66 peptide as bait, we developed several phagederived Abs against GPIIIa49-66 that exhibit comparable antigen-binding capacity.…”