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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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Regulation of Humoral Immune Responses and B Cell Tolerance by the IgM Fc Receptor (FcμR). ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1254:75-86. [DOI: 10.1007/978-981-15-3532-1_7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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Kubagawa H, Honjo K, Ohkura N, Sakaguchi S, Radbruch A, Melchers F, Jani PK. Functional Roles of the IgM Fc Receptor in the Immune System. Front Immunol 2019; 10:945. [PMID: 31130948 PMCID: PMC6509151 DOI: 10.3389/fimmu.2019.00945] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Accepted: 04/12/2019] [Indexed: 12/14/2022] Open
Abstract
It is now evident from studies of mice unable to secrete IgM that both non-immune “natural” and antigen-induced “immune” IgM are important for protection against pathogens and for regulation of immune responses to self-antigens. Since identification of its Fc receptor (FcμR) by a functional cloning strategy in 2009, the roles of FcμR in these IgM effector functions have begun to be explored. Unlike Fc receptors for switched Ig isotypes (e.g., FcγRs, FcεRs, FcαR, Fcα/μR, pIgR, FcRn), FcμR is selectively expressed by lymphocytes: B, T, and NK cells in humans and only B cells in mice. FcμR may have dual signaling ability: one through a potential as yet unidentified adaptor protein non-covalently associating with the FcμR ligand-binding chain via a His in transmembrane segment and the other through its own Tyr and Ser residues in the cytoplasmic tail. FcμR binds pentameric and hexameric IgM with a high avidity of ~10 nM in solution, but more efficiently binds IgM when it is attached to a membrane component via its Fab region on the same cell surface (cis engagement). Four different laboratories have generated Fcmr-ablated mice and eight different groups of investigators have examined the resultant phenotypes. There have been some clear discrepancies reported that appear to be due to factors including differences in the exons of Fcmr that were targeted to generate the knockouts. One common feature among these different mutant mice, however, is their propensity to produce autoantibodies of both IgM and IgG isotypes. In this review, we briefly describe recent findings concerning the functions of FcμR in both mice and humans and propose a model for how FcμR plays a regulatory role in B cell tolerance.
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Affiliation(s)
| | - Kazuhito Honjo
- Department of Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Naganari Ohkura
- Immunology Frontier Research Center, Osaka University, Osaka, Japan
| | - Shimon Sakaguchi
- Immunology Frontier Research Center, Osaka University, Osaka, Japan
| | | | | | - Peter K Jani
- Deutsches Rheuma-Forschungszentrum, Berlin, Germany
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Liu J, Wang Y, Xiong E, Hong R, Lu Q, Ohno H, Wang JY. Role of the IgM Fc Receptor in Immunity and Tolerance. Front Immunol 2019; 10:529. [PMID: 30967868 PMCID: PMC6438924 DOI: 10.3389/fimmu.2019.00529] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2018] [Accepted: 02/27/2019] [Indexed: 11/13/2022] Open
Abstract
Immunoglobulin (Ig) M is the first antibody isotype to appear during evolution, ontogeny and immune responses. IgM not only serves as the first line of host defense against infections but also plays an important role in immune regulation and immunological tolerance. For many years, IgM is thought to function by binding to antigen and activating complement system. With the discovery of the IgM Fc receptor (FcμR), it is now clear that IgM can also elicit its function through FcμR. In this review, we will describe the molecular characteristics of FcμR, its role in B cell development, maturation and activation, humoral immune responses, host defense, and immunological tolerance. We will also discuss the functional relationship between IgM-complement and IgM-FcμR pathways in regulating immunity and tolerance. Finally, we will discuss the potential involvement of FcμR in human diseases.
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Affiliation(s)
- Jun Liu
- Department of Immunology, School of Basic Medical Sciences, Fudan University, Shanghai, China
| | - Ying Wang
- Department of Immunology, School of Basic Medical Sciences, Fudan University, Shanghai, China
| | - Ermeng Xiong
- Department of Immunology, School of Basic Medical Sciences, Fudan University, Shanghai, China
| | - Rongjian Hong
- Department of Immunology, School of Basic Medical Sciences, Fudan University, Shanghai, China
| | - Qing Lu
- Department of Immunology, School of Basic Medical Sciences, Fudan University, Shanghai, China
| | - Hiroshi Ohno
- RIKEN Center for Integrative Medical Sciences, Kanagawa, Japan
| | - Ji-Yang Wang
- Department of Immunology, School of Basic Medical Sciences, Fudan University, Shanghai, China
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Shaw TN, Inkson CA, Villegas-Mendez A, Pattinson DJ, Strangward P, Else KJ, Draper SJ, Zeef LAH, Couper KN. Infection-Induced Resistance to Experimental Cerebral Malaria Is Dependent Upon Secreted Antibody-Mediated Inhibition of Pathogenic CD8 + T Cell Responses. Front Immunol 2019; 10:248. [PMID: 30846985 PMCID: PMC6394254 DOI: 10.3389/fimmu.2019.00248] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2018] [Accepted: 01/29/2019] [Indexed: 12/27/2022] Open
Abstract
Cerebral malaria (CM) is one of the most severe complications of Plasmodium falciparum infection. There is evidence that repeated parasite exposure promotes resistance against CM. However, the immunological basis of this infection-induced resistance remains poorly understood. Here, utilizing the Plasmodium berghei ANKA (PbA) model of experimental cerebral malaria (ECM), we show that three rounds of infection and drug-cure protects against the development of ECM during a subsequent fourth (4X) infection. Exposure-induced resistance was associated with specific suppression of CD8+ T cell activation and CTL-related pathways, which corresponded with the development of heterogeneous atypical B cell populations as well as the gradual infection-induced generation and maintenance of high levels of anti-parasite IgG. Mechanistically, transfer of high-titer anti-parasite IgG did not protect 1X infected mice against ECM and depletion of atypical and regulatory B cells during 4X infection failed to abrogate infection-induced resistance to ECM. However, IgMi mice that were unable to produce secreted antibody, or undergo class switching, during the repeated rounds of infection failed to develop resistance against ECM. The failure of infection-induced protection in IgMi mice was associated with impaired development of atypical B cell populations and the inability to suppress pathogenic CD8+ T cell responses. Our results, therefore, suggest the importance of anti-parasite antibody responses, gradually acquired, and maintained through repeated Plasmodium infections, for modulating the B cell compartment and eventually suppressing memory CD8+ T cell reactivation to establish infection-induced resistance to ECM.
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Affiliation(s)
- Tovah N. Shaw
- Faculty of Biology, Medicine and Health, The Lydia Becker Institute of Immunology and Inflammation, University of Manchester, Manchester, United Kingdom
- Manchester Collaborative Centre for Inflammation Research, The Lydia Becker Institute of Immunology and Inflammation, University of Manchester, Manchester, United Kingdom
| | - Colette A. Inkson
- Faculty of Biology, Medicine and Health, The Lydia Becker Institute of Immunology and Inflammation, University of Manchester, Manchester, United Kingdom
| | - Ana Villegas-Mendez
- Faculty of Biology, Medicine and Health, The Lydia Becker Institute of Immunology and Inflammation, University of Manchester, Manchester, United Kingdom
| | | | - Patrick Strangward
- Faculty of Biology, Medicine and Health, The Lydia Becker Institute of Immunology and Inflammation, University of Manchester, Manchester, United Kingdom
| | - Kathryn J. Else
- Faculty of Biology, Medicine and Health, The Lydia Becker Institute of Immunology and Inflammation, University of Manchester, Manchester, United Kingdom
| | - Simon J. Draper
- The Jenner Institute, University of Oxford, Oxford, United Kingdom
| | - Leo A. H. Zeef
- Faculty of Biology, Medicine and Health, University of Manchester, Manchester, United Kingdom
| | - Kevin N. Couper
- Faculty of Biology, Medicine and Health, The Lydia Becker Institute of Immunology and Inflammation, University of Manchester, Manchester, United Kingdom
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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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Sellau J, Alvarado CF, Hoenow S, Mackroth MS, Kleinschmidt D, Huber S, Jacobs T. IL-22 dampens the T cell response in experimental malaria. Sci Rep 2016; 6:28058. [PMID: 27311945 PMCID: PMC4911577 DOI: 10.1038/srep28058] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2016] [Accepted: 05/31/2016] [Indexed: 01/21/2023] Open
Abstract
A tight regulation between the pro- and anti-inflammatory immune responses during plasmodial infection is of crucial importance, since a disruption leads to severe malaria pathology. IL-22 is a member of the IL-10 cytokine family, which is known to be highly important in immune regulation. We could detect high plasma levels of IL-22 in Plasmodium falciparum malaria as well as in Plasmodium berghei ANKA (PbA)-infected C57BL/6J mice. The deficiency of IL-22 in mice during PbA infection led to an earlier occurrence of cerebral malaria but is associated with a lower parasitemia compared to wt mice. Furthermore, at an early time point of infection T cells from PbA-infected Il22(-/-) mice showed an enhanced IFNγ but a diminished IL-17 production. Moreover, dendritic cells from Il22(-/-) mice expressed a higher amount of the costimulatory ligand CD86 upon infection. This finding can be corroborated in vitro since bone marrow-derived dendritic cells from Il22(-/-) mice are better inducers of an antigen-specific IFNγ response by CD8(+) T cells. Even though there is no IL-22 receptor complex known on hematopoietic cells, our data suggest a link between IL-22 and the adaptive immune system which is currently not identified.
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Affiliation(s)
- Julie Sellau
- Bernhard-Nocht-Institute for Tropical Medicine, Bernhard-Nocht-Straße 74, 20359 Hamburg, Germany
| | | | - Stefan Hoenow
- Bernhard-Nocht-Institute for Tropical Medicine, Bernhard-Nocht-Straße 74, 20359 Hamburg, Germany
| | - Maria Sophie Mackroth
- Bernhard-Nocht-Institute for Tropical Medicine, Bernhard-Nocht-Straße 74, 20359 Hamburg, Germany
- University Medical Center Hamburg-Eppendorf, I. Department of Medicine, Martinistraße 52, 20246 Hamburg, Germany
| | - Dörte Kleinschmidt
- University Medical Center Hamburg-Eppendorf, I. Department of Medicine, Martinistraße 52, 20246 Hamburg, Germany
| | - Samuel Huber
- University Medical Center Hamburg-Eppendorf, I. Department of Medicine, Martinistraße 52, 20246 Hamburg, Germany
| | - Thomas Jacobs
- Bernhard-Nocht-Institute for Tropical Medicine, Bernhard-Nocht-Straße 74, 20359 Hamburg, Germany
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Wang H, Coligan JE, Morse HC. Emerging Functions of Natural IgM and Its Fc Receptor FCMR in Immune Homeostasis. Front Immunol 2016; 7:99. [PMID: 27014278 PMCID: PMC4791374 DOI: 10.3389/fimmu.2016.00099] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2016] [Accepted: 02/29/2016] [Indexed: 01/02/2023] Open
Abstract
Most natural IgM antibodies are encoded by germline Ig sequences and are produced in large quantities by both mice and humans in the absence of intentional immunization. Natural IgM are reactive with many conserved epitopes, including those shared by microorganisms and autoantigens. As a result, these antibodies play important roles in clearing intruding pathogens, as well as apoptotic/necrotic cells and otherwise damaged tissues. While natural IgM binds to target structures with low affinity due to a lack of significant selection by somatic hypermutation, its pentameric structure with 10 antigen-binding sites enables these antibodies to bind multivalent target antigens with high avidity. Opsonization of antigen complexed with IgM is mediated by cell surface Fc receptors. While the existence of Fc alpha/mu receptor has been known for some time, only recently has the Fc receptor specific for IgM (FCMR) been identified. In this review, we focus on our current understandings of how natural IgM and FCMR regulate the immune system and maintain homeostasis under physiological and pathological conditions.
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Affiliation(s)
- Hongsheng Wang
- Virology and Cellular Immunology Section, Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health , Rockville, MD , USA
| | - John E Coligan
- Receptor Cell Biology Section, Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health , Rockville, MD , USA
| | - Herbert C Morse
- Virology and Cellular Immunology Section, Laboratory of Immunogenetics, National Institute of Allergy and Infectious Diseases, National Institutes of Health , Rockville, MD , USA
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