Functional Roles of the IgM Fc Receptor in the Immune System

Functional Roles of the IgM Fc Receptor in the Immune System Hiromi Kubagawa1*, Kazuhito Honjo2, Naganari Ohkura3, Shimon Sakaguchi3, Andreas Radbruch1, Fritz Melchers1* and Peter K. Jani1* 1Deutsches Rheuma-Forschungszentrum, Berlin, Germany2Department of Medicine, School of Medicine, University of Alabama at Birmingham, Birmingham, AL, United States3Immunology Frontier Research Center, Osaka University, Osaka, Japan 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, bu...
Source: Frontiers in Immunology - Category: Allergy & Immunology Source Type: research