Identification of TOSO/FAIM3 as an Fc receptor for IgM.
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, Fcalpha/muR 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 (FcmuR). FcmuR protein was expressed predominantly on B-lineage cells; expression of the Fcmr transcripts was observed from the pre-B-cell stage and maintained thereafter during B-cell development. These results identify TOSO/FAIM3 as a receptor for IgM and suggest that FcmuR may serve as an uptake receptor for IgM-opsonized antigens by B cells.
Shima
Hideaki
H
Division of Immunobiology, Graduate School of Nanobioscience, Yokohama City University, Yokohama, Kanagawa 230-0045, Japan.
Takatsu
Hiroyuki
H
Fukuda
Shinji
S
Ohmae
Masumi
M
Hase
Koji
K
Kubagawa
Hiromi
H
Wang
Ji-Yang
JY
Ohno
Hiroshi
H
D000595:Amino Acid Sequence; D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D016175:B-Lymphocyte Subsets / Q000276:immunology* / Q000378:metabolism; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D002469:Cell Separation; D005434:Flow Cytometry; D006367:HeLa Cells; D006801:Humans; D007075:Immunoglobulin M / Q000276:immunology* / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D011961:Receptors, Fc / Q000276:immunology* / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D014162:Transfection
D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; C112037:FCMR protein, human; C499656:Fcmr protein, mouse; D007075:Immunoglobulin M; D008565:Membrane Proteins; D011961:Receptors, Fc