Identification of TOSO/FAIM3 as an Fc receptor for IgM

Hideaki Shima, Hiroyuki Takatsu, Shinji Fukuda, Masumi Ohmae, Koji Hase, Hiromi Kubagawa, Ji Yang Wang, Hiroshi Ohno

Research output: Contribution to journalArticlepeer-review

100 Citations (Scopus)


Fc receptors specifically bind to the Fc region of Igs to mediate the unique functions to each class of Igs. To identify a novel Fc receptor for IgM, we searched expressed sequence tag database for molecules containing Ig domains with homology to those of known Fc receptors for IgM, Fca/μR and polymeric Ig receptor. As a result, we identified TOSO/Fas apoptotic inhibitory molecule 3 (FAIM3) as a possible Fc receptor for IgM. HeLa cells transfected with a TOSO/FAIM3-expression vector bound to IgM but not IgG and were able to internalize IgM-conjugated beads but not IgG-conjugated beads, suggesting that TOSO/FAIM3 is indeed a receptor for IgM (FcμR). FcmR protein was expressed predominantly on B-lineage cells; expression of the Fcmr transcripts was observed from the pre-β-cell stage and maintained thereafter during B-cell development. These results identify TOSO/FAIM3 as a receptor for IgM and suggest that FcμR may serve as an uptake receptor for IgM-opsonized antigens by B cells.

Original languageEnglish
Article numberdxp121
Pages (from-to)149-156
Number of pages8
JournalInternational immunology
Issue number3
Publication statusPublished - 2009 Dec 30
Externally publishedYes


  • B cell
  • Fc receptor
  • IgM

ASJC Scopus subject areas

  • Immunology and Allergy
  • Immunology


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