Abstract
Most healthy adults are protected from meningococcal disease by the presence of naturally acquired anti-meningococcal antibodies; however, the identity of the target antigens of this protective immunity remains unclear, particularly for protection against serogroup B disease. To identify the protein targets of natural protective immunity we developed an immunoprecipitation and proteomics approach to define the immunoproteome of the meningococcus. Sera from 10 healthy individuals showing serum bactericidal activity against both a meningococcal C strain (L91543) and the B strain MC58, together with commercially available pooled human sera were used as probe anti-sera. Immunoprecipitation was performed with each serum sample and live cells from both meningococcal strains. Immunoprecipitated proteins were identified by mass spectrometry. Analysis of the immunoproteome from each serum demonstrated both pan-reactive antigens that were recognised by most sera as well as subject-specific antigens. Most antigens were found in both meningococcal strains but a few were strain-specific. Many of the immunoprecipitated proteins have previously been characterised as surface antigens including adhesins and proteases, several of which have been recognised as vaccine candidate antigens e.g. fHBP, NadA and NHBA. The data clearly demonstrates the presence of meningococcal antibodies in healthy individuals with no history of meningococcal infection and a wide diversity of immune responses. The identification of the immuno-reactive proteins of the meningococcus provides a basis for understanding the role of each antigen in the natural immunity associated with carriage and may help to design vaccination strategies.