Monoclonal antibodies specific for human IgM Fc receptor inhibit ligand-binding activity.
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ABSTRACT: A panel of six different murine hybridoma clones secreting IgG monoclonal antibodies (MAbs) specific for the human IgM Fc receptor (Fc?R) was generated. All MAbs specifically precipitated a major protein of ?60?kDa from membrane lysates of Fc?R-bearing, but not Fc?R-negative, cells as did IgM-ligands. Pre-incubation of membrane lysate of Fc?R-bearing cells with these MAbs completely removed the ?60?kDa IgM-reactive protein. By using recombinant human/mouse chimeric Fc?R proteins, the epitope recognized by HM7 and HM10 MAbs was mapped to the Ig-like domain of human Fc?R, whereas the other MAbs recognized the stalk region. Pre-incubation of Fc?R(+) 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 Fc?R(+) cells were simultaneously incubated with both IgM-ligands and MAbs, HM7 MAb efficiently competed with IgM for Fc?R binding. Unlike control Jurkat cells, Fc?R-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 Fc?R, thereby promoting apoptosis of Fc?R-bearing Jurkat cells. The variable regions of the HM7 MAb were composed of Ighv14-3, Ighd1-2, and Ighj2 for the ?2b heavy chain and Igk3-4 and Igkj2 for the ? light chain. These findings suggest that HM7 MAb efficiently blocks the ligand-binding activity of Fc?R.
SUBMITTER: Kubagawa Y
PROVIDER: S-EPMC4278172 | biostudies-literature | 2014 Dec
REPOSITORIES: biostudies-literature
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