Immunogenicity of peptides derived from a fibronectin-binding protein of S. aureus expressed on two different plant viruses

The D2 peptide derived from an S. aureus fibronectin-binding protein (FnBP) was expressed on the surface of the icosahedral cowpea mosaic virus (amino acids 1-30 of D2) or on the rod-shaped potato virus X (amino acids 1-38 of D2), termed CPMV-MAST1 and PVX-MAST8, respectively. Mice and rats were immunized subcutaneously with CPMV-MAST1 and mice with PVX-MAST8 in adjuvant and high titres of FnBP-specific antibody were obtained. The mouse IgG was predominantly of the IgG2a and IgG2b isotypes, which strongly bound complement component C1q, suggesting a TH1-bias in the peptide-specific responses. Sera from mice and rats immunized with CPMV-MAST1 and from mice immunized with PVX-MAST8 were shown to completely inhibit the binding of fibronectin to immobilised recombinant FnBP and rat sera against CPMV-MAST1 were able to block adherence of S. aureus to fibronectin. These studies demonstrate that the D2 peptide is highly immunogenic when expressed on 2 different plant viruses and highlight the potential of plant virus-based vaccines to protect against S. aureus infections.