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Werner LM, Criss AK. Diverse Functions of C4b-Binding Protein in Health and Disease. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2023; 211:1443-1449. [PMID: 37931209 PMCID: PMC10629839 DOI: 10.4049/jimmunol.2300333] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Accepted: 05/26/2023] [Indexed: 11/08/2023]
Abstract
C4b-binding protein (C4BP) is a fluid-phase complement inhibitor that prevents uncontrolled activation of the classical and lectin complement pathways. As a complement inhibitor, C4BP also promotes apoptotic cell death and is hijacked by microbes and tumors for complement evasion. Although initially characterized for its role in complement inhibition, there is an emerging recognition that C4BP functions in a complement-independent manner to promote cell survival, protect against autoimmune damage, and modulate the virulence of microbial pathogens. In this Brief Review, we summarize the structure and functions of human C4BP, with a special focus on activities that extend beyond the canonical role of C4BP in complement inhibition.
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Affiliation(s)
- Lacie M. Werner
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia School of Medicine, Charlottesville, VA, USA
| | - Alison K. Criss
- Department of Microbiology, Immunology, and Cancer Biology, University of Virginia School of Medicine, Charlottesville, VA, USA
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Li S, Bettoni S, Mohlin F, Geoghegan JA, Blom AM, Laabei M. Recruitment of C4b-binding protein is not a complement evasion strategy employed by Staphylococcus aureus. MICROBIOLOGY (READING, ENGLAND) 2023; 169:001391. [PMID: 37668351 PMCID: PMC10569063 DOI: 10.1099/mic.0.001391] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2023] [Accepted: 08/23/2023] [Indexed: 09/06/2023]
Abstract
Complement offers a first line of defence against infection through the opsonization of microbial pathogens, recruitment of professional phagocytes to the infection site and the coordination of inflammatory responses required for the resolution of infection. Staphylococcus aureus is a successful pathogen that has developed multiple mechanisms to thwart host immune responses. Understanding the precise strategies employed by S. aureus to bypass host immunity will be paramount for the development of vaccines and or immunotherapies designed to prevent or limit infection. To gain a better insight into the specific immune evasion mechanisms used by S. aureus we examined the pathogen's interaction with the soluble complement inhibitor, C4b-binding protein (C4BP). Previous studies indicated that S. aureus recruits C4BP using a specific cell-wall-anchored surface protein and that bound C4BP limits complement deposition on the staphylococcal surface. Using flow-cytometric-based bacterial-protein binding assays we observed no interaction between S. aureus and C4BP. Moreover, we offer a precautionary warning that C4BP isolated from plasma can be co-purified with minute quantities of human IgG, which can distort binding analysis between S. aureus and human-derived proteins. Combined our data indicates that recruitment of C4BP is not a complement evasion strategy employed by S. aureus.
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Affiliation(s)
- Shuxian Li
- Department of Life Sciences, University of Bath, Bath, BA2 7AY, UK
| | - Serena Bettoni
- Department of Life Sciences, University of Bath, Bath, BA2 7AY, UK
- Division of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Malmö, Sweden
| | - Frida Mohlin
- Division of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Malmö, Sweden
| | - Joan A. Geoghegan
- Institute of Microbiology and Infection, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
| | - Anna M. Blom
- Division of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Malmö, Sweden
| | - Maisem Laabei
- Department of Life Sciences, University of Bath, Bath, BA2 7AY, UK
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Thofte O, Bettoni S, Su YC, Thegerström J, Jonsson S, Mattsson E, Sandblad L, Martí S, Garmendia J, Blom AM, Riesbeck K. Nontypeable Haemophilus influenzae P5 Binds Human C4b-Binding Protein, Promoting Serum Resistance. THE JOURNAL OF IMMUNOLOGY 2021; 207:1566-1577. [PMID: 34433620 PMCID: PMC8428749 DOI: 10.4049/jimmunol.2100105] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/02/2021] [Accepted: 07/14/2021] [Indexed: 01/03/2023]
Abstract
Exposure of P5 at the surface of NTHi positively correlates with C4BP binding. C4BP bound to the bacterial surface retains its complement inhibitory capacity. C4BP binding to P5 is important for NTHi serum resistance.
Nontypeable Haemophilus influenzae (NTHi) is a Gram-negative human pathogen that causes infections mainly in the upper and lower respiratory tract. The bacterium is associated with bronchitis and exacerbations in patients suffering from chronic obstructive pulmonary disease and frequently causes acute otitis media in preschool children. We have previously demonstrated that the binding of C4b binding protein (C4BP) is important for NTHi complement evasion. In this study, we identified outer membrane protein 5 (P5) of NTHi as a novel ligand of C4BP. Importantly, we observed significantly lower C4BP binding and decreased serum resistance in P5-deficient NTHi mutants. Surface expression of recombinant P5 on Escherichia coli conferred C4BP binding and consequently increased serum resistance. Moreover, P5 expression was positively correlated with C4BP binding in a series of clinical isolates. We revealed higher levels of P5 surface expression and consequently more C4BP binding in isolates from the lower respiratory tract of chronic obstructive pulmonary disease patients and tonsil specimens compared with isolates from the upper respiratory tract and the bloodstream (invasive strains). Our results highlight P5 as an important protein for protecting NTHi against complement-mediated killing.
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Affiliation(s)
- Oskar Thofte
- Clinical Microbiology, Department of Translational Medicine, Faculty of Medicine, Lund University, Malmö, Sweden
| | - Serena Bettoni
- Protein Chemistry, Department of Translational Medicine, Faculty of Medicine, Lund University, Malmö, Sweden
| | - Yu-Ching Su
- Clinical Microbiology, Department of Translational Medicine, Faculty of Medicine, Lund University, Malmö, Sweden
| | - John Thegerström
- Clinical Microbiology, Department of Translational Medicine, Faculty of Medicine, Lund University, Malmö, Sweden
| | - Sandra Jonsson
- Clinical Microbiology, Department of Translational Medicine, Faculty of Medicine, Lund University, Malmö, Sweden
| | - Emma Mattsson
- Clinical Microbiology, Department of Translational Medicine, Faculty of Medicine, Lund University, Malmö, Sweden
| | - Linda Sandblad
- Department of Molecular Biology, Umeå University, Umea, Sweden
| | - Sara Martí
- Microbiology Department, Research Network for Respiratory Diseases, Bellvitge Institute for Biomedical Research, Bellvitge University Hospital, Barcelona, Spain; and
| | - Junkal Garmendia
- Instituto de Agrobiotecnología, Consejo Superior de Investigaciones Científicas-Gobierno de Navarra, Mutilva, Spain
| | - Anna M Blom
- Protein Chemistry, Department of Translational Medicine, Faculty of Medicine, Lund University, Malmö, Sweden
| | - Kristian Riesbeck
- Clinical Microbiology, Department of Translational Medicine, Faculty of Medicine, Lund University, Malmö, Sweden;
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