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Articles by H Kubagawa
Total Records ( 2 ) for H Kubagawa
  H Shima , H Takatsu , S Fukuda , M Ohmae , K Hase , H Kubagawa , J. Y Wang and H. Ohno
 

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, Fc/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). FcµR 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 FcµR may serve as an uptake receptor for IgM-opsonized antigens by B cells.

  H Kubagawa , S Oka , Y Kubagawa , I Torii , E Takayama , D. W Kang , G. L Gartland , L. F Bertoli , H Mori , H Takatsu , T Kitamura , H Ohno and J. Y. Wang
 

Although Fc receptors (FcRs) for switched immunoglobulin (Ig) isotypes have been extensively characterized, FcR for IgM (FcµR) has defied identification. By retroviral expression and functional cloning, we have identified a complementary DNA (cDNA) encoding a bona fide FcµR in human B-lineage cDNA libraries. FcµR is defined as a transmembrane sialoglycoprotein of ~60 kD, which contains an extracellular Ig-like domain homologous to two other IgM-binding receptors (polymeric Ig receptor and Fc/µR) but exhibits an exclusive Fcµ-binding specificity. The cytoplasmic tail of FcµR contains conserved Ser and Tyr residues, but none of the Tyr residues match the immunoreceptor tyrosine-based activation, inhibitory, or switch motifs. Unlike other FcRs, the major cell types expressing FcµR are adaptive immune cells, including B and T lymphocytes. After antigen-receptor ligation or phorbol myristate acetate stimulation, FcµR expression was up-regulated on B cells but was down-modulated on T cells, suggesting differential regulation of FcµR expression during B and T cell activation. Although this receptor was initially designated as Fas apoptotic inhibitory molecule 3, or TOSO, our results indicate that FcµR per se has no inhibitory activity in Fas-mediated apoptosis and that such inhibition is only achieved when anti-Fas antibody of an IgM but not IgG isotype is used for inducing apoptosis.

 
 
 
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