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Front Immunol. 2019 Jan 11;9:3139. doi: 10.3389/fimmu.2018.03139. eCollection 2018.

Utilization of Staphylococcal Immune Evasion Protein Sbi as a Novel Vaccine Adjuvant.

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Department of Biology and Biochemistry, University of Bath, Bath, United Kingdom.
Hamburg Unit, European Molecular Biology Laboratory, Deutsches Elektronen-Synchrotron, Hamburg, Germany.
Institute of Cellular Medicine, Newcastle University, Newcastle-upon-Tyne, United Kingdom.
Dynamic Biosensors GmbH, Martinsried, Germany.
Department of Chemistry, University of Bath, Bath, United Kingdom.
Department of Pharmacy and Pharmacology, University of Bath, Bath, United Kingdom.


Co-ligation of the B cell antigen receptor with complement receptor 2 on B-cells via a C3d-opsonised antigen complex significantly lowers the threshold required for B cell activation. Consequently, fusions of antigens with C3d polymers have shown great potential in vaccine design. However, these linear arrays of C3d multimers do not mimic the natural opsonisation of antigens with C3d. Here we investigate the potential of using the unique complement activating characteristics of Staphylococcal immune-evasion protein Sbi to develop a pro-vaccine approach that spontaneously coats antigens with C3 degradation products in a natural way. We show that Sbi rapidly triggers the alternative complement pathway through recruitment of complement regulators, forming tripartite complexes that act as competitive antagonists of factor H, resulting in enhanced complement consumption. These functional results are corroborated by the structure of the complement activating Sbi-III-IV:C3d:FHR-1 complex. Finally, we demonstrate that Sbi, fused with Mycobacterium tuberculosis antigen Ag85b, causes efficient opsonisation with C3 fragments, thereby enhancing the immune response significantly beyond that of Ag85b alone, providing proof of concept for our pro-vaccine approach.


Staphycoccus aureus; adjuvant; complement; immune evasion; vaccine

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