Identification and characterization of a protective immunodominant B cell epitope of pertactin (P.69) from Bordetella pertussis

Epitopes defined by monoclonal antibodies (mAb) specific for the Bordetella pertussis outer membrane protein P.69 (pertactin) were mapped using a series of amino‐ and carboxy‐terminal deletion mutants expressed in Escherichia coli. mAb were found to bind predominantly to a region of pertactin spanning a (Pro‐Gln‐Pro)₅ repeat motif and one mAb was found to bind to another region spanning a (Gly‐Gly‐X_aa‐X_aa‐Pro)₅ repeat motif. To localize further the mAb‐binding sites, a panel of synthetic peptides, a series of 94 overlapping hexameric peptides, and a P.69 30‐amino acid fusion to a hepatitis B core protein (HBcAg‐69), were synthesized. This combined approach has identified the binding site for the mAb BBO5: Pro‐Gly‐Pro‐Gln‐Pro‐Pro; mAb BBO7, E4A8 and E4D7: Ala‐Pro‐Gln‐Pro‐Pro‐Ala‐Gly‐Arg; and mAb BPE3: Thr‐Leu‐Trp‐Tyr‐Ala‐Glu‐Ser‐Asn‐Ala‐Leu‐Ser‐Lys‐Arg. We have used a non‐lethal murine respiratory model of B. pertussis infection to investigate the ability of a peptide containing the epitope of the mAb BBO5 to elicit protective immunity. Immunization of mice with the HBcAg‐69 protein prevented growth of B. pertussis in the lungs compared to mice receiving HBcAg alone, and protection correlated with high titers of anti‐P.69 antibodies.