title: Antibody-dependent infection of human macrophages by severe acute respiratory syndrome coronavirus.
abstract: BACKGROUND
  Public health risks associated to infection by human coronaviruses remain considerable and vaccination is a key option for preventing the resurgence of severe acute respiratory syndrome coronavirus (SARS-CoV). We have previously reported that antibodies elicited by a SARS-CoV vaccine candidate based on recombinant, full-length SARS-CoV Spike-protein trimers, trigger infection of immune cell lines. These observations prompted us to investigate the molecular mechanisms and responses to antibody-mediated infection in human macrophages.
  
  
  METHODS
  We have used primary human immune cells to evaluate their susceptibility to infection by SARS-CoV in the presence of anti-Spike antibodies. Fluorescence microscopy and real-time quantitative reverse transcriptase polymerase chain reaction (RT-PCR) were utilized to assess occurrence and consequences of infection. To gain insight into the underlying molecular mechanism, we performed mutational analysis with a series of truncated and chimeric constructs of fragment crystallizable γ receptors (FcγR), which bind antibody-coated pathogens.
  
  
  RESULTS
  We show here that anti-Spike immune serum increased infection of human monocyte-derived macrophages by replication-competent SARS-CoV as well as Spike-pseudotyped lentiviral particles (SARS-CoVpp). Macrophages infected with SARS-CoV, however, did not support productive replication of the virus. Purified anti-viral IgGs, but not other soluble factor(s) from heat-inactivated mouse immune serum, were sufficient to enhance infection. Antibody-mediated infection was dependent on signaling-competent members of the human FcγRII family, which were shown to confer susceptibility to otherwise naïve ST486 cells, as binding of immune complexes to cell surface FcγRII was necessary but not sufficient to trigger antibody-dependent enhancement (ADE) of infection. Furthermore, only FcγRII with intact cytoplasmic signaling domains were competent to sustain ADE of SARS-CoVpp infection, thus providing additional information on the role of downstream signaling by FcγRII.
  
  
  CONCLUSIONS
  These results demonstrate that human macrophages can be infected by SARS-CoV as a result of IgG-mediated ADE and indicate that this infection route requires signaling pathways activated downstream of binding to FcγRII receptors.
authors.forename: Ming Shum
authors.initials: MS
authors.lastname: Yip
authors.forename: Nancy Hiu Lan
authors.initials: NH
authors.lastname: Leung
authors.forename: Chung Yan
authors.initials: CY
authors.lastname: Cheung
authors.forename: Ping Hung
authors.initials: PH
authors.lastname: Li
authors.forename: Horace Hok Yeung
authors.initials: HH
authors.lastname: Lee
authors.forename: Marc
authors.initials: M
authors.lastname: Daëron
authors.forename: Joseph Sriyal Malik
authors.initials: JS
authors.lastname: Peiris
authors.affiliation: HKU-Pasteur Research Pole and Center of Influenza Research, School of Public Health, LKS Faculty of Medicine, The University of Hong Kong, Hong Kong, Hong Kong SAR. bruzzone@hku.hk.
authors.forename: Roberto
authors.initials: R
authors.lastname: Bruzzone
authors.forename: Martial
authors.initials: M
authors.lastname: Jaume
mesh_terms: D000914:Antibodies, Viral / Q000276:immunology*; D002478:Cells, Cultured; D004705:Endocytosis; D006801:Humans; D008264:Macrophages / Q000821:virology*; D008856:Microscopy, Fluorescence; D060888:Real-Time Polymerase Chain Reaction; D045473:Severe acute respiratory syndrome-related coronavirus / Q000502:physiology*
chemical_list: D000914:Antibodies, Viral