title: Optimal activation of Fc-mediated effector functions by influenza virus hemagglutinin antibodies requires two points of contact.
abstract: Influenza virus strain-specific monoclonal antibodies (mAbs) provide protection independent of Fc gamma receptor (FcγR) engagement. In contrast, optimal in vivo protection achieved by broadly reactive mAbs requires Fc-FcγR engagement. Most strain-specific mAbs target the head domain of the viral hemagglutinin (HA), whereas broadly reactive mAbs typically recognize epitopes within the HA stalk. This observation has led to questions regarding the mechanism regulating the activation of Fc-dependent effector functions by broadly reactive antibodies. To dissect the molecular mechanism responsible for this dichotomy, we inserted the FLAG epitope into discrete locations on HAs. By characterizing the interactions of several FLAG-tagged HAs with a FLAG-specific antibody, we show that in addition to Fc-FcγR engagement mediated by the FLAG-specific antibody, a second intermolecular bridge between the receptor-binding region of the HA and sialic acid on effector cells is required for optimal activation. Inhibition of this second molecular bridge, through the use of an F(ab')2or the mutation of the sialic acid-binding site, renders the Fc-FcγR interaction unable to optimally activate effector cells. Our findings indicate that broadly reactive mAbs require two molecular contacts to possibly stabilize the immunologic synapse and potently induce antibody-dependent cell-mediated antiviral responses: (i) the interaction between the Fc of a mAb bound to HA with the FcγR of the effector cell and (ii) the interaction between the HA and its sialic acid receptor on the effector cell. This concept might be broadly applicable for protective antibody responses to viral pathogens that have suitable receptors on effector cells.
authors.affiliation: Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029; Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Leon
authors.affiliation: Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029; Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029.
authors.forename: Wenqian
authors.initials: W
authors.lastname: He
authors.affiliation: Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029.
authors.forename: Caitlin E
authors.initials: CE
authors.lastname: Mullarkey
authors.affiliation: Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029; Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Bailey
authors.affiliation: Department of Biochemistry and Biomedical Sciences, Institute of Infectious Diseases Research, McMaster Immunology Research Centre, McMaster University, Hamilton, ON, Canada L8S 4K1.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Miller
authors.affiliation: Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029.
authors.forename: Florian
authors.initials: F
authors.lastname: Krammer
authors.affiliation: Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029; peter.palese@mssm.edu gene.tan@mssm.edu.
authors.forename: Peter
authors.initials: P
authors.lastname: Palese
authors.affiliation: Department of Microbiology, Icahn School of Medicine at Mount Sinai, New York, NY 10029; peter.palese@mssm.edu gene.tan@mssm.edu.
authors.forename: Gene S
authors.initials: GS
authors.lastname: Tan
mesh_terms: D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000378:metabolism; D000914:Antibodies, Viral / Q000737:chemistry / Q000276:immunology*; D000920:Antibody-Dependent Cell Cytotoxicity; D000939:Epitopes / Q000737:chemistry; D057809:HEK293 Cells; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry / Q000276:immunology*; D006801:Humans; D007111:Immunity, Cellular; D008954:Models, Biological; D008958:Models, Molecular; D019158:N-Acetylneuraminic Acid / Q000378:metabolism; D009975:Orthomyxoviridae / Q000276:immunology*; D011961:Receptors, Fc / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D000914:Antibodies, Viral; D000939:Epitopes; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D011961:Receptors, Fc; D019158:N-Acetylneuraminic Acid
keywords: Fcγ receptor; antibody-dependent cell-mediated immunity; broadly reactive antibodies; hemagglutinin; influenza virus