title: Monoclonal antibodies specific for human IgM Fc receptor inhibit ligand-binding activity.
abstract: A panel of six different murine hybridoma clones secreting IgG monoclonal antibodies (MAbs) specific for the human IgM Fc receptor (FcμR) was generated. All MAbs specifically precipitated a major protein of ∼60 kDa from membrane lysates of FcμR-bearing, but not FcμR-negative, cells as did IgM-ligands. Pre-incubation of membrane lysate of FcμR-bearing cells with these MAbs completely removed the ∼60 kDa IgM-reactive protein. By using recombinant human/mouse chimeric FcμR proteins, the epitope recognized by HM7 and HM10 MAbs was mapped to the Ig-like domain of human FcμR, whereas the other MAbs recognized the stalk region. Pre-incubation of FcμR(+) cells with the Ig-like domain-specific MAbs, but not with others, markedly inhibited subsequent IgM-ligand binding. A similar, but much weaker, inhibition was also observed when the incubation order was reversed. When FcμR(+) cells were simultaneously incubated with both IgM-ligands and MAbs, HM7 MAb efficiently competed with IgM for FcμR binding. Unlike control Jurkat cells, FcμR-bearing cells were resistant to apoptosis induced by agonistic IgM anti-Fas MAb (CH11); however, addition of the HM7 MAb inhibited the interaction of the Fc portion of CH11 MAb with FcμR, thereby promoting apoptosis of FcμR-bearing Jurkat cells. The variable regions of the HM7 MAb were composed of Ighv14-3, Ighd1-2, and Ighj2 for the γ2b heavy chain and Igk3-4 and Igkj2 for the κ light chain. These findings suggest that HM7 MAb efficiently blocks the ligand-binding activity of FcμR.
authors.affiliation: Division of Laboratory Medicine, Department of Pathology, University of Alabama at Birmingham , Alabama.
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Kubagawa
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Honjo
authors.forename: Dong-Won
authors.initials: DW
authors.lastname: Kang
authors.forename: Hiromi
authors.initials: H
authors.lastname: Kubagawa
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000096:biosynthesis* / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D001483:Base Sequence; D017931:DNA Primers / Q000235:genetics; D005455:Fluorescent Antibody Technique; D006801:Humans; D006825:Hybridomas / Q000276:immunology / Q000378:metabolism*; D007075:Immunoglobulin M / Q000378:metabolism; D047468:Immunoprecipitation; D019169:Jurkat Cells; D008024:Ligands; D051379:Mice; D008969:Molecular Sequence Data; D011485:Protein Binding; D011961:Receptors, Fc / Q000276:immunology* / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA
chemical_list: D000911:Antibodies, Monoclonal; D017931:DNA Primers; D007075:Immunoglobulin M; D008024:Ligands; D011961:Receptors, Fc; C035311:immunoglobulin M receptor