Background: B-Type natriuretic peptide (BNP 1-32 ) as well as the N-terminal fragment of the prohormone containing residues 1-76 (NT-proBNP 1-76 ), both cleavage products of the precursor proBNP 1-108 , are reported to be powerful markers for prognosis and risk stratification of heart failure. However, the intact precursor also circulates in the bloodstream. Assays for the detection of these cleavage products have been developed, but most of these assays may overestimate the concentrations of the cleavage products because they also measure the precursor form. It is therefore important to develop an immunoassay that specifically measures solely proBNP 1-108 in plasma. Methods: After carefully designing the peptide used to immunize mice, we selected a specific monoclonal antibody (mAb Hinge76) that recognizes the cleavage site of proBNP 1-108 , an epitope present only in the precursor form. mAb Hinge76 recognizes recombinant proBNP 1-108 in a dose-dependent manner, without any significant cross-reactivity with either recombinant NT-proBNP 1-76 or synthetic BNP 1-32 . By combining mAb Hinge76 with a polyclonal antibody directed against BNP 1-32 , we were able to set up a proBNP 1-108 -specific sandwich immunoassay able to confirm the presence of proBNP 1-108 in blood samples. Results: From a cohort of 50 healthy persons and 170 patients with congestive heart failure (CHF), our assay was able to differentiate healthy individuals from CHF patients (P <0.005). Interestingly, plasma proBNP 1-108

IntroductionSoluble immune aggregates bearing intact Fc fragments are effective treatment for a variety of autoimmune disorders in mice. The better to understand the mechanisms by which Fc-bearing immune complexes suppress autoimmunity, and to develop a platform for clinical translation, we created a series of fully recombinant forms of polyvalent IgG2a Fc, termed stradomers, and tested their efficacy in a therapeutic model of collagen-induced arthritis (CIA) and preventive models of both idiopathic thrombocytopenic purpura (ITP) and graft-versus-host disease (GVHD).MethodsStradomers were created by engineering either the human IgG2 hinge sequence (IgG2H) or the isoleucine zipper (ILZ) onto either the carboxy or amino termini of murine IgG2a Fc. Multimerization and binding to the canonical Fc receptors and the C-type lectin SIGN-RI were evaluated by using sodium dodecylsulfate-polymerase chain reaction (SDS-PAGE) and Biacore/Octet assays. The efficacy of stradomers in alleviating CIA and preventing ITP and GVHD was compared with "gold standard" therapies, including prednisolone and intravenous immune globulin (IVIG).ResultsStradomers exist as both homodimeric and highly ordered sequential multimers. Higher-order multimers demonstrate increasingly stable associations with the canonic Fcγ receptors (FcγRs), and SIGN-R1, and are more effective than Fc homodimers in treating CIA. Furthermore, stradomers confer partial protection against platelet loss in a murine model ITP, but do not prevent GVHD.ConclusionThese data suggest that fully human stradomers might serve as valuable tools for the treatment of selected autoimmune disorders and as reagents to study the function of Fc:FcR interactions in vivo.

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Key Points• GL-2045, a recombinant human IgG1-based Fc multimer, binds C1q and inhibits complementdependent cytotoxicity.• GL-2045 induces selflimited complement activation that is governed by both factors H and I and results in the generation of iC3b.