title: Recombinant CD16A-Ig forms a homodimer and cross-blocks the ligand binding functions of neutrophil and monocyte Fcgamma receptors.
abstract: Receptors for the Fc region of IgG (FcgammaR) are expressed as membrane-bound and soluble forms in inflammatory cells. These receptors mediate a variety of immunoregulatory functions. FcgammaR-bearing neutrophils and macrophages play a major role in mediating immune complex induced inflammatory diseases and antibody-mediated tissue injury in autoimmune diseases. To delineate the biological role of the soluble FcgammaR, a recombinant soluble CD16A (CD16A-Ig) was expressed and characterized. CD16A-Ig is secreted as a disulfide-linked homodimer of 70kDa. The purified CD16A-Ig bound to human IgG1 and IgG3 immobilized onto ELISA plates and on IgG1- and IgG3-coated erythrocytes. Saturation binding studies and Scatchard plot analysis showed that immune complex bound to the purified CD16A-Ig with high avidity. Moreover, CD16A-Ig competitively blocked the binding of cell surface-expressed CD16A-CHO cells to IgG-coated plates. The dimeric CD16A-Ig also efficiently cross-blocked the binding of IgG-coated target cells to other FcgammaR expressed on neutrophils and monocytes. These results demonstrate that CD16A-Ig forms a high avidity dimer and is capable of blocking cell-cell interactions mediated by inflammatory cells expressing FcgammaR and IgG-coated target cells. These findings suggest that the dimeric FcgammaR molecules could be used therapeutically for the intervention of immune complex-mediated inflammatory disease.
authors.affiliation: Schools of Mechanical Engineering and Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
authors.forename: Ping
authors.initials: P
authors.lastname: Li
authors.forename: Shanmugam
authors.initials: S
authors.lastname: Nagarajan
authors.forename: Cheng
authors.initials: C
authors.lastname: Zhu
authors.forename: Periasamy
authors.initials: P
authors.lastname: Selvaraj
mesh_terms: D000818:Animals; D002450:Cell Communication / Q000276:immunology; D003432:Cross-Linking Reagents; D019281:Dimerization; D018922:HL-60 Cells; D006801:Humans; D006825:Hybridomas; D007136:Immunoglobulins / Q000276:immunology* / Q000378:metabolism; D020014:K562 Cells; D008024:Ligands; D051379:Mice; D009000:Monocytes / Q000276:immunology*; D009504:Neutrophils / Q000276:immunology*; D017452:Receptors, IgG / Q000276:immunology* / Q000378:metabolism; D011994:Recombinant Proteins / Q000276:immunology / Q000378:metabolism; D015398:Signal Transduction / Q000276:immunology*
chemical_list: D003432:Cross-Linking Reagents; D007136:Immunoglobulins; D008024:Ligands; D017452:Receptors, IgG; D011994:Recombinant Proteins