title: A human monoclonal antibody that specifically binds and inhibits the staphylococcal complement inhibitor protein SCIN.
abstract: Staphylococcus aureus is a serious public health burden causing a wide variety of infections. Earlier detection of such infections could result in faster and more directed therapies that also prevent resistance development. Human monoclonal antibodies (humAbs) are promising tools for diagnosis and therapy owing to their relatively straightforward synthesis, long history of safe clinical use and high target specificity. Here we show that the humAb 6D4, which was obtained from a random screen of B-cells producing antibodies that bind to whole cells of S. aureus, targets the staphylococcal complement inhibitor (SCIN). The epitope recognized by 6D4 was localized to residues 26 to 36 in the N-terminus of SCIN, which overlap with the active site. Accordingly, 6D4 can inhibit SCIN activity as demonstrated through the analysis of C3b deposition on S. aureus cells and complement-induced lysis of rabbit erythrocytes. Importantly, while SCIN is generally regarded as a secreted virulence factor, 6D4 allowed detection of strongly increased SCIN binding to S. aureus cells upon exposure to human serum, relating to the known binding of SCIN to C3 convertases deposited on the staphylococcal cell surface. Lastly, we show that labeling of humAb 6D4 with a near-infrared fluorophore allows one-step detection of SCIN-producing S. aureus cells. Together, our findings show that the newly described humAb 6D4 specifically recognizes S. aureus SCIN, which can potentially be used for detection of human serum-incubated S. aureus strains expressing SCIN.
authors.affiliation: a Department of Medical Microbiology , University of Groningen, University Medical Center Groningen , Groningen , The Netherlands.
authors.forename: Hedzer
authors.initials: H
authors.lastname: Hoekstra
authors.affiliation: a Department of Medical Microbiology , University of Groningen, University Medical Center Groningen , Groningen , The Netherlands.
authors.forename: Francisco
authors.initials: F
authors.lastname: Romero Pastrana
authors.affiliation: b IQ Therapeutics , Groningen , The Netherlands.
authors.forename: Hendrik P J
authors.initials: HPJ
authors.lastname: Bonarius
authors.affiliation: c Medical Microbiology, University Medical Center Utrecht , Utrecht , The Netherlands.
authors.forename: Kok P M
authors.initials: KPM
authors.lastname: van Kessel
authors.affiliation: b IQ Therapeutics , Groningen , The Netherlands.
authors.forename: Goffe S
authors.initials: GS
authors.lastname: Elsinga
authors.affiliation: b IQ Therapeutics , Groningen , The Netherlands.
authors.forename: Neeltje
authors.initials: N
authors.lastname: Kooi
authors.affiliation: b IQ Therapeutics , Groningen , The Netherlands.
authors.forename: Herman
authors.initials: H
authors.lastname: Groen
authors.affiliation: a Department of Medical Microbiology , University of Groningen, University Medical Center Groningen , Groningen , The Netherlands.
authors.forename: Jan Maarten
authors.initials: JM
authors.lastname: van Dijl
authors.affiliation: a Department of Medical Microbiology , University of Groningen, University Medical Center Groningen , Groningen , The Netherlands.
authors.forename: Girbe
authors.initials: G
authors.lastname: Buist
mesh_terms: D000818:Animals; D000907:Antibodies, Bacterial / Q000737:chemistry / Q000378:metabolism*; D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000378:metabolism*; D000942:Antigens, Bacterial / Q000737:chemistry / Q000378:metabolism*; D020134:Catalytic Domain; D050577:Complement C3-C5 Convertases / Q000378:metabolism; D003179:Complement C3b / Q000378:metabolism; D051056:Complement Inactivating Agents / Q000737:chemistry / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000737:chemistry; D006801:Humans; D008856:Microscopy, Fluorescence; D011485:Protein Binding; D011817:Rabbits; D013203:Staphylococcal Infections / Q000276:immunology*; D013211:Staphylococcus aureus / Q000472:pathogenicity*; D037521:Virulence Factors / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000907:Antibodies, Bacterial; D000911:Antibodies, Monoclonal; D000942:Antigens, Bacterial; D051056:Complement Inactivating Agents; D005456:Fluorescent Dyes; D037521:Virulence Factors; D003179:Complement C3b; D050577:Complement C3-C5 Convertases
keywords: C3b; Monoclonal antibody; SCIN; Staphylococcus aureus; complement