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Mahmoudi Aliabadi P, Teuber R, Jani PK, Wilson L, Enghard P, Barnes S, Chiorazzi N, Radbruch A, Melchers F, Kubagawa H. Soluble Fc Receptor for IgM in Sera From Subsets of Patients With Chronic Lymphocytic Leukemia as Determined by a New Mouse Monoclonal Antibody. Front Immunol 2022; 13:863895. [PMID: 35784336 PMCID: PMC9245419 DOI: 10.3389/fimmu.2022.863895] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2022] [Accepted: 05/06/2022] [Indexed: 11/15/2022] Open
Abstract
The FcR for IgM (FcµR) is the newest member of the FcR family, selectively expressed by lymphocytes, and distinct from FcRs for switched Ig isotypes that are expressed by various immune cell types and non-hematopoietic cells. From studies of Fcmr-ablated mice, FcµR was shown to have a regulatory function in B-cell tolerance, as evidenced by high serum titers of autoantibodies of the IgM and IgG isotypes in mutant mice. In our previous studies, both cell-surface and serum FcµR levels were elevated in patients with chronic lymphocytic leukemia (CLL), where antigen-independent self-ligation of BCR is a hallmark of the neoplastic B cells. This was assessed by sandwich ELISA using two different ectodomain-specific mAbs. To determine whether the serum FcµR is derived from cleavage of its cell-surface receptor (shedding) or its alternative splicing to skip the transmembrane exon resulting in a 70-aa unique hydrophilic C-terminus (soluble), we developed a new mouse IgG1κ mAb specific for human soluble FcμR (solFcμR) by taking advantages of the unique nature of transductant stably producing His-tagged solFcµR and of an in vivo differential immunization. His-tagged solFcμR attached to exosomes and plasma membranes, allowing immunization and initial hybridoma screening without purification of solFcμR. Differential immunization with tolerogen (membrane FcμR) and immunogen (solFcμR) also facilitated to generate solFcμR-specific hybridomas. The resultant solFcμR-specific mAb reacted with serum FcµR in subsets of CLL patients. This mAb, along with another ectodomain-specific mAb, will be used for verifying the hypothesis that the production of solFcµR is the consequence of chronic stimulation of BCR.
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Affiliation(s)
| | - Ruth Teuber
- Humoral Immune Regulation, Deutsches Rheuma-Forschungszentrum, Berlin, Germany
| | - Peter K. Jani
- Lymphocyte Development, Deutsches Rheuma-Forschungszentrum, Berlin, Germany
| | - Landon Wilson
- Targeted Metabolomics and Proteomics Laboratory, Department of Pharmacology and Toxicology, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Philipp Enghard
- Department of Nephrology and Medical Intensive Care, Charité-Universitätsmedizin, Berlin, Germany
| | - Stephen Barnes
- Targeted Metabolomics and Proteomics Laboratory, Department of Pharmacology and Toxicology, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Nicholas Chiorazzi
- Karches Center for Oncology Research, Feinstein Institute for Medical Research, Manhasset, NY, United States
| | - Andreas Radbruch
- Cell Biology, Deutsches Rheuma-Forschungszentrum, Berlin, Germany
| | - Fritz Melchers
- Lymphocyte Development, Deutsches Rheuma-Forschungszentrum, Berlin, Germany
| | - Hiromi Kubagawa
- Humoral Immune Regulation, Deutsches Rheuma-Forschungszentrum, Berlin, Germany
- *Correspondence: Hiromi Kubagawa,
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Skopnik CM, Al-Qaisi K, Calvert RA, Enghard P, Radbruch A, Sutton BJ, Kubagawa H. Identification of Amino Acid Residues in Human IgM Fc Receptor (FcµR) Critical for IgM Binding. Front Immunol 2021; 11:618327. [PMID: 33584711 PMCID: PMC7873564 DOI: 10.3389/fimmu.2020.618327] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Accepted: 12/03/2020] [Indexed: 11/17/2022] Open
Abstract
Both non-immune “natural” and antigen-induced “immune” IgM are important for protection against infections and for regulation of immune responses to self-antigens. The roles of its Fc receptor (FcµR) in these IgM effector functions have begun to be explored. In the present study, by taking advantage of the difference in IgM-ligand binding of FcµRs of human (constitutive binding) and mouse (transient binding), we replaced non-conserved amino acid residues of human FcµR with mouse equivalents before establishment of cell lines stably expressing mutant or wild-type (WT) receptors. The resultant eight-different mutant FcµR-bearing cells were compared with WT receptor-bearing cells for cell-surface expression and IgM-binding by flow cytometric assessments using receptor-specific mAbs and IgM paraproteins as ligands. Three sites Asn66, Lys79-Arg83, and Asn109, which are likely in the CDR2, DE loop and CDR3 of the human FcµR Ig-like domain, respectively, were responsible for constitutive IgM binding. Intriguingly, substitution of Glu41 and Met42 in the presumed CDR1 with the corresponding mouse residues Gln and Leu, either single or more prominently in combination, enhanced both the receptor expression and IgM binding. A four-aa stretch of Lys24-Gly27 in the predicted A ß-strand of human FcµR appeared to be essential for maintenance of its proper receptor conformation on plasma membranes because of reduction of both receptor expression and IgM-binding potential when these were mutated. Results from a computational structural modeling analysis were consistent with these mutational data and identified a possible mode of binding of FcµR with IgM involving the loops including Asn66, Arg83 and Asn109 of FcµR interacting principally with the Cµ4 domain including Gln510 and to a lesser extent Cµ3 domain including Glu398, of human IgM. To our knowledge, this is the first experimental report describing the identification of amino acid residues of human FcµR critical for binding to IgM Fc.
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Affiliation(s)
| | - Khlowd Al-Qaisi
- Humoral Immune Regulation, Deutsches Rheuma-Forschungszentrum, Berlin, Germany
| | - Rosaleen A Calvert
- Randall Centre for Cell and Molecular Biophysics, King's College London, London, United Kingdom
| | - Philipp Enghard
- Department of Nephrology and Medical Intensive Care, Charité-Universitätmedizin, Berlin, Germany
| | - Andreas Radbruch
- Humoral Immune Regulation, Deutsches Rheuma-Forschungszentrum, Berlin, Germany
| | - Brian J Sutton
- Randall Centre for Cell and Molecular Biophysics, King's College London, London, United Kingdom
| | - Hiromi Kubagawa
- Humoral Immune Regulation, Deutsches Rheuma-Forschungszentrum, Berlin, Germany
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Kubagawa H, Skopnik CM, Zimmermann J, Durek P, Chang HD, Yoo E, Bertoli LF, Honjo K, Radbruch A. Authentic IgM Fc Receptor (FcμR). Curr Top Microbiol Immunol 2017; 408:25-45. [PMID: 28702710 DOI: 10.1007/82_2017_23] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Since the bona fide Fc receptor for IgM antibody (FcµR) was identified eight years ago, much progress has been made in defining its biochemical nature, cellular distribution, and effector function. However, there are clearly conflicting results, especially about the cellular distribution and function of murine FcµR. In this short article, we will discuss recent findings from us and other investigators along with our interpretations and comments that may help to resolve the existing puzzles and should open new avenues of investigation.
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Affiliation(s)
- Hiromi Kubagawa
- Deutsches Rheuma-Forschungszentrum in Berlin, 10117, Berlin, Germany.
| | | | - Jakob Zimmermann
- Deutsches Rheuma-Forschungszentrum in Berlin, 10117, Berlin, Germany
| | - Pawel Durek
- Deutsches Rheuma-Forschungszentrum in Berlin, 10117, Berlin, Germany
| | - Hyun-Dong Chang
- Deutsches Rheuma-Forschungszentrum in Berlin, 10117, Berlin, Germany
| | - Esther Yoo
- Department of Microbiology, Immunology and Molecular Genetics, University of California, Los Angeles, CA, 90095, USA
| | | | - Kazuhito Honjo
- Department of Medicine, University of Alabama at Birmingham, Birmingham, AL, 35209, USA
| | - Andreas Radbruch
- Deutsches Rheuma-Forschungszentrum in Berlin, 10117, Berlin, Germany
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Kubagawa H, Carroll MC, Jacob CO, Lang KS, Lee KH, Mak T, McAndrews M, Morse HC, Nolan GP, Ohno H, Richter GH, Seal R, Wang JY, Wiestner A, Coligan JE. Nomenclature of Toso, Fas apoptosis inhibitory molecule 3, and IgM FcR. THE JOURNAL OF IMMUNOLOGY 2015; 194:4055-7. [PMID: 25888699 DOI: 10.4049/jimmunol.1500222] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Hiromi Kubagawa and John E. Coligan coordinated an online meeting to define an appropriate nomenclature for the cell surface glycoprotein presently designated by different names: Toso, Fas apoptosis inhibitory molecule 3 (FAIM3), and IgM FcR (FcμR). FAIM3 and Faim3 are the currently approved symbols for the human and mouse genes, respectively, in the National Center for Biotechnology Information, Ensembl, and other databases. However, recent functional results reported by several groups of investigators strongly support a recommendation for renaming FAIM3/Faim3 as FCMR/Fcmr, a name better reflecting its physiological function as the FcR for IgM. Participants included 12 investigators involved in studying Toso/FAIM3(Faim3)/FμR, representatives from the Human Genome Nomenclature Committee (Ruth Seal) and the Mouse Genome Nomenclature Committee (Monica McAndrews), and an observer from the IgM research field (Michael Carroll). In this article, we provide a brief background of the key research on the Toso/FAIM3(Faim3)/FcμR proteins, focusing on the ligand specificity and functional activity, followed by a brief summary of discussion about adopting a single name for this molecule and its gene and a resulting recommendation for genome nomenclature committees.
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Affiliation(s)
- Hiromi Kubagawa
- Department of Pathology, University of Alabama at Birmingham, Birmingham, AL 35294;
| | | | - Chaim O Jacob
- Department of Medicine, University of Southern California School of Medicine, Los Angeles, CA 90033
| | - Karl S Lang
- Institute for Immunology, University of Duisburg-Essen, Essen 45147, Germany
| | - Kyeong-Hee Lee
- Institute for Clinical Chemistry, Hannover Medical School, Hannover 30625, Germany
| | - Tak Mak
- Campbell Family Institute for Breast Cancer Research, Princess Margaret Cancer Centre/University Health Network, Toronto, Ontario M5T 2M9, Canada
| | - Monica McAndrews
- Mouse Genome Informatics, Jackson Laboratory, Bar Harbor, ME 04609
| | - Herbert C Morse
- Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852
| | - Garry P Nolan
- Department of Microbiology and Immunology, Stanford University, Stanford, CA 94305
| | - Hiroshi Ohno
- Laboratory for Intestinal Ecosystem, RIKEN Center for Integrative Medical Sciences, Yokohama, Kanagawa 230-0045, Japan
| | - Günther H Richter
- Kinderklinik, Klinikum Rechts der Isar, Technische Universität München, Munich 81664, Germany
| | - Ruth Seal
- Human Genome Organisation Gene Nomenclature Committee, European Bioinformatics Institute, Wellcome Trust Genome Campus Hinxton, Cambridgeshire CB10 1SD, United Kingdom
| | - Ji-Yang Wang
- Department of Immunology, School of Basic Medical Sciences, Fudan University, Shanghai 200032, China; and
| | - Adrian Wiestner
- Hematology Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892
| | - John E Coligan
- Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852;
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Six MAbs Specific for Human FcμR (HM2, HM3, HM6, HM7, HM10, and HM14). Monoclon Antib Immunodiagn Immunother 2014. [DOI: 10.1089/mab.2014.0083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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