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Kubagawa H, Mahmoudi Aliabadi P, Al-Qaisi K, Jani PK, Honjo K, Izui S, Radbruch A, Melchers F. Functions of IgM fc receptor (FcµR) related to autoimmunity. Autoimmunity 2024; 57:2323563. [PMID: 38465789 DOI: 10.1080/08916934.2024.2323563] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2023] [Accepted: 02/20/2024] [Indexed: 03/12/2024]
Abstract
Unlike Fc receptors for switched immunoglobulin (Ig) isotypes, Fc receptor for IgM (FcµR) is selectively expressed by lymphocytes. The ablation of the FcµR gene in mice impairs B cell tolerance as evidenced by concomitant production of autoantibodies of IgM and IgG isotypes. In this essay, we reiterate the autoimmune phenotypes observed in mutant mice, ie IgM homeostasis, dysregulated humoral immune responses including autoantibodies, and Mott cell formation. We also propose the potential phenotypes in individuals with FCMR deficiency and the model for FcµR-mediated regulation of self-reactive B cells.
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Affiliation(s)
| | | | | | - Peter K Jani
- Deutsches Rheuma-Forschungszentrum Berlin, Berlin, Germany
| | - Kazuhito Honjo
- Department of Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, USA
| | - Shozo Izui
- Department of Pathology and Immunology, University of Geneva, Geneva, Switzerland
| | | | - Fritz Melchers
- Deutsches Rheuma-Forschungszentrum Berlin, Berlin, Germany
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Mahmoudi Aliabadi P, Al-Qaisi K, Jani PK, Honjo K, Klemm U, Lee KH, Baumgarth N, Radbruch A, Melchers F, Kubagawa H. Enhanced Mott cell formation linked with IgM Fc receptor (FcμR) deficiency. Eur J Immunol 2023; 53:e2250315. [PMID: 37098762 DOI: 10.1002/eji.202250315] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Revised: 03/31/2023] [Accepted: 04/25/2023] [Indexed: 04/27/2023]
Abstract
In previous studies, Mott cells, an unusual form of plasma cells containing Ig-inclusion bodies, were frequently observed in peripheral lymphoid tissues in our IgM Fc receptor (FcμR)-deficient (KO) mouse strain. Because of discrepancies in the reported phenotypes of different Fcmr KO mouse strains, we here examined two additional available mutant strains and confirmed that such enhanced Mott-cell formation was a general phenomenon associated with FcμR deficiency. Splenic B cells from Fcmr KO mice clearly generated more Mott cells than those from WT mice when stimulated in vitro with LPS alone or a B-1, but not B-2, activation cocktail. Nucleotide sequence analysis of the Ig variable regions of a single IgMλ+ Mott-hybridoma clone developed from splenic B-1 B cells of Fcmr KO mice revealed the near (VH) or complete (Vλ) identity with the corresponding germline gene segments and the addition of six or five nucleotides at the VH/DH and DH/JH junctions, respectively. Transduction of an FcμR cDNA into the Mott hybridoma significantly reduced cells containing IgM-inclusion bodies with a concomitant increase in IgM secretion, leading to secreted IgM binding to FcμR expressed on Mott transductants. These findings suggest a regulatory role of FcμR in the formation of Mott cells and IgM-inclusion bodies.
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Affiliation(s)
| | - Khlowd Al-Qaisi
- Humoral Immune Regulation, Deutsches Rheuma-Forschungszentrum (DRFZ), Berlin, Germany
| | - Peter K Jani
- Lymphocyte Development, Deutsches Rheuma-Forschungszentrum (DRFZ), Berlin, Germany
| | - Kazuhito Honjo
- Department of Medicine, School of Medicine, University of Alabama, Birmingham, USA
| | - Uwe Klemm
- Experimental Animals, Max Planck Institute for Infectious Biology, Berlin, Germany
| | - Kyeong-Hee Lee
- Inflammation Research Group, Institute of Clinical Chemistry, Hannover Medical School, Hanover, Germany
| | - Nicole Baumgarth
- Department of Molecular Microbiology and immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, USA
| | - Andreas Radbruch
- Department of Cell Biology, Deutsches Rheuma-Forschungszentrum, DRFZ), Berlin, Germany
| | - Fritz Melchers
- Lymphocyte Development, Deutsches Rheuma-Forschungszentrum (DRFZ), Berlin, Germany
| | - Hiromi Kubagawa
- Humoral Immune Regulation, Deutsches Rheuma-Forschungszentrum (DRFZ), Berlin, Germany
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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Honjo K, Kubagawa Y, Suzuki Y, Takagi M, Ohno H, Bucy RP, Izui S, Kubagawa H. Enhanced auto-antibody production and Mott cell formation in FcμR-deficient autoimmune mice. Int Immunol 2014; 26:659-72. [PMID: 24994818 DOI: 10.1093/intimm/dxu070] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The IgM-Fc receptor (FcμR) is involved in IgM homeostasis as evidenced by increased pre-immune serum IgM and natural auto-antibodies of both IgM and IgG isotypes in Fcmr-deficient C57BL/6 (B6) mice. To determine the impact of Fcmr-ablation on autoimmunity, we introduced the Fcmr null mutation onto the Fas-deficient autoimmune-prone B6.MRL Fas (lpr/lpr) mouse background (B6/lpr). Both IgM and IgG auto-antibodies against dsDNA or chromatin appeared earlier in FcμR(-) B6/lpr than FcμR(+) B6/lpr mice, but this difference became less pronounced with age. Splenic B2 cells, which were 2-fold elevated in FcμR(+) B6/lpr mice, were reduced to normal B6 levels in FcμR(-) B6/lpr mice, whereas splenic B1 cells were comparable in both groups of B6/lpr mice. By contrast, marginal zone (MZ) B cells were markedly reduced in FcμR(-) B6/lpr mice compared with either FcμR(+) B6/lpr or wild type (WT) B6 mice. This reduction appeared to result from rapid differentiation of MZ B cells into plasma cells in the absence of FcμR, as IgM antibody to a Smith (Sm) antigen, to which MZ B cells are known to preferentially respond, was greatly increased in both groups (B6/lpr and B6) of FcμR(-) mice compared with FcμR(+) B6/lpr or B6 mice. Mott cells, aberrant plasma cells with intra-cytoplasmic inclusions, were also increased in the absence of FcμR. Despite these abnormalities, the severity of renal pathology and function and survival were all indistinguishable between FcμR(-) and FcμR(+) B6/lpr mice. Collectively, these findings suggest that FcμR plays important roles in the regulation of auto-antibody production, Mott cell formation and the differentiation of MZ B cells into plasma cells in B6.MRL Fas (lpr/lpr) mice.
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Affiliation(s)
- Kazuhito Honjo
- Department of Pathology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - Yoshiki Kubagawa
- Department of Pathology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - Yusuke Suzuki
- Department of Internal Medicine, Division of Nephrology, Juntendo University School of Medicine, Tokyo 113-8421, Japan
| | - Miyuki Takagi
- Department of Internal Medicine, Division of Nephrology, Juntendo University School of Medicine, Tokyo 113-8421, Japan
| | - Hiroshi Ohno
- Laboratory for Intestinal Ecosystem, RIKEN Center for Integrative Medical Sciences, Yokohama 230-0045, Japan
| | - R Pat Bucy
- Department of Pathology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - Shozo Izui
- Department of Pathology and Immunology, University of Geneva, 1211 Geneva 4, Switzerland
| | - Hiromi Kubagawa
- Department of Pathology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
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Abstract
Receptor editing is a mechanism of self-tolerance used in newly generated B cells. The expressed heavy (H) or light (L) chain of an autoreactive receptor is replaced by upstream V genes which eliminate or modify autoreactivity. Editing of anti-DNA receptors has been characterized in anti-DNA transgenic mouse models including 3H9, 3H9/56R, and their revertant 3H9GL. Certain L chains, termed editors, rescue anti-DNA B cells by neutralizing or modifying DNA binding of the H chain. This editing mechanism acts on the natural H chain repertoire; endogenous H chains with anti-DNA features are expressed primarily in combination with editor L chains. We ask whether a similar set of L chains exists in the human repertoire, and if so, do they edit H chains with anti-DNA signatures? We compared the protein sequences of mouse editors to all human L chains and found several human L chains similar to mouse editors. These L chains diminish or veto anti-DNA binding when expressed with anti-DNA H chains. The human H chains expressed with these L chains also have relatively high arginine (Arg) content in the H chain complementarity determining region (H3), suggesting that receptor editing plays a role in establishing tolerance to DNA in humans.
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Affiliation(s)
- Olga Kalinina
- Gwen Knapp Center for Lupus and Immunology Research, Department of Pathology, University of Chicago, Chicago, IL 60637
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Radic M, Weigert MG, Khan SN, Han J, Kalinina O, Luning Prak ET. Antibodies that bind complex glycosaminoglycans accumulate in the Golgi. Proc Natl Acad Sci U S A 2013; 110:11958-63. [PMID: 23818632 DOI: 10.1073/pnas.1308620110] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Light (L) chains that edit anti-DNA heavy (H) chains rescue B-cell development by suppressing DNA binding. However, exceptional editor L chains allow B cells to reach splenic compartments even though their B-cell receptors remain autoreactive. Such incompletely edited B cells express multireactive antibodies that accumulate in the Golgi and are released as insoluble, amyloid-like immune complexes. Here, we examine examples of incomplete editing from the analysis of variable to joining (VJ) gene junction of the variable (Vλx) editor L chain. When paired with the anti-DNA heavy chain, VH56R, the Vλx variants yield antibodies with differing specificities, including glycosaminoglycan reactivity. Our results implicate these specificities in the evasion of receptor editing through intracellular sequestration of IgM and the release of insoluble IgM complexes. Our findings can be extrapolated to human L chains and have implications for understanding a latent component of the Ig repertoire that could exert pathogenic and protective functions.
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