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      Competition for FcRn-mediated transport gives rise to short half-life of human IgG3 and offers therapeutic potential

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          Abstract

          Human IgG3 displays the strongest effector functions of all IgG subclasses but has a short half-life for unresolved reasons. Here we show that IgG3 binds to IgG-salvage receptor (FcRn), but that FcRn-mediated transport and rescue of IgG3 is inhibited in the presence of IgG1 due to intracellular competition between IgG1 and IgG3. We reveal that this occurs because of a single amino acid difference at position 435, where IgG3 has an arginine instead of the histidine found in all other IgG subclasses. While the presence of R435 in IgG increases binding to FcRn at neutral pH, it decreases binding at acidic pH, affecting the rescue efficiency—but only in the presence of H435–IgG. Importantly, we show that in humans the half-life of the H435-containing IgG3 allotype is comparable to IgG1. H435–IgG3 also gave enhanced protection against a pneumococcal challenge in mice, demonstrating H435–IgG3 to be a candidate for monoclonal antibody therapies.

          Abstract

          The half-life of IgG is regulated by binding to the neonatal Fc receptor and, in the case of IgG3, is reduced compared to other IgG proteins. In this study, a mutation in IgG3 is shown to reduce binding to the neonatal Fc receptor, which can be competitively blocked by IgG1.

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          Most cited references 52

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          VMD: visual molecular dynamics.

          VMD is a molecular graphics program designed for the display and analysis of molecular assemblies, in particular biopolymers such as proteins and nucleic acids. VMD can simultaneously display any number of structures using a wide variety of rendering styles and coloring methods. Molecules are displayed as one or more "representations," in which each representation embodies a particular rendering method and coloring scheme for a selected subset of atoms. The atoms displayed in each representation are chosen using an extensive atom selection syntax, which includes Boolean operators and regular expressions. VMD provides a complete graphical user interface for program control, as well as a text interface using the Tcl embeddable parser to allow for complex scripts with variable substitution, control loops, and function calls. Full session logging is supported, which produces a VMD command script for later playback. High-resolution raster images of displayed molecules may be produced by generating input scripts for use by a number of photorealistic image-rendering applications. VMD has also been expressly designed with the ability to animate molecular dynamics (MD) simulation trajectories, imported either from files or from a direct connection to a running MD simulation. VMD is the visualization component of MDScope, a set of tools for interactive problem solving in structural biology, which also includes the parallel MD program NAMD, and the MDCOMM software used to connect the visualization and simulation programs. VMD is written in C++, using an object-oriented design; the program, including source code and extensive documentation, is freely available via anonymous ftp and through the World Wide Web.
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            SWISS-MODEL and the Swiss-PdbViewer: an environment for comparative protein modeling.

            Comparative protein modeling is increasingly gaining interest since it is of great assistance during the rational design of mutagenesis experiments. The availability of this method, and the resulting models, has however been restricted by the availability of expensive computer hardware and software. To overcome these limitations, we have developed an environment for comparative protein modeling that consists of SWISS-MODEL, a server for automated comparative protein modeling and of the SWISS-PdbViewer, a sequence to structure workbench. The Swiss-PdbViewer not only acts as a client for SWISS-MODEL, but also provides a large selection of structure analysis and display tools. In addition, we provide the SWISS-MODEL Repository, a database containing more than 3500 automatically generated protein models. By making such tools freely available to the scientific community, we hope to increase the use of protein structures and models in the process of experiment design.
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              Specificity and affinity of human Fcgamma receptors and their polymorphic variants for human IgG subclasses.

              Distinct genes encode 6 human receptors for IgG (hFcgammaRs), 3 of which have 2 or 3 polymorphic variants. The specificity and affinity of individual hFcgammaRs for the 4 human IgG subclasses is unknown. This information is critical for antibody-based immunotherapy which has been increasingly used in the clinics. We investigated the binding of polyclonal and monoclonal IgG1, IgG2, IgG3, and IgG4 to FcgammaRI; FcgammaRIIA, IIB, and IIC; FcgammaRIIIA and IIIB; and all known polymorphic variants. Wild-type and low-fucosylated IgG1 anti-CD20 and anti-RhD mAbs were also examined. We found that (1) IgG1 and IgG3 bind to all hFcgammaRs; (2) IgG2 bind not only to FcgammaRIIA(H131), but also, with a lower affinity, to FcgammaRIIA(R131) and FcgammaRIIIA(V158); (3) IgG4 bind to FcgammaRI, FcgammaRIIA, IIB and IIC and FcgammaRIIIA(V158); and (4) the inhibitory receptor FcgammaRIIB has a lower affinity for IgG1, IgG2, and IgG3 than all other hFcgammaRs. We also identified parameters that determine the specificity and affinity of hFcgammaRs for IgG subclasses. These results document how hFcgammaR specificity and affinity may account for the biological activities of antibodies. They therefore highlight the role of specific hFcgammaRs in the therapeutic and pathogenic effects of antibodies in disease.
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                Author and article information

                Journal
                Nat Commun
                Nature Communications
                Nature Publishing Group
                2041-1723
                20 December 2011
                : 2
                : 599
                Affiliations
                [1 ]simpleDepartment of Experimental Immunohematology, Sanquin Research, and Landsteiner Laboratory, Academic Medical Center, University of Amsterdam , Plesmanlaan 125, Amsterdam 1066 CX, The Netherlands.
                [2 ]simpleDepartment of Immunology, Oslo University Hospital Rikshospitalet and University of Oslo , PO Box 4950 Nydalen, Oslo 0424, Norway.
                [3 ]simpleCentre for Immune Regulation and Department of Molecular Biosciences, University of Oslo , PO box 1041, Blindern, Oslo 0316, Norway.
                [4 ]simpleDepartment of Medical Microbiology, University Medical Center Utrecht , Heidelberglaan 100, 3584 CX, The Netherlands.
                [5 ]simpleDepartment of Immunology, Landspitali University Hospital, Faculty of Medicine, University of Iceland , Eiriksgata, hus 14, Reykjavik 101, Iceland.
                [6 ]simpleDepartment of Pharmacology, Utrecht University , Universiteitsweg 99, Utrecht 3584 CG, The Netherlands.
                [7 ]These authors contributed equally to this work.
                Author notes
                Article
                ncomms1608
                10.1038/ncomms1608
                3247843
                22186895
                Copyright © 2011, Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.

                This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/

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