IMMUNOGENICITY OF SYNTHETIC PEPTIDES OF HAEMOPHILUS-INFLUENZAE TYPE-BOUTER-MEMBRANE PROTEIN P1

To identify the B- and T-cell epitopes of P1 of Haemophilus influenzae type b, 13 peptides covering 90% of the protein were chemically synth esized. Mouse, guinea pig, and rabbit antisera raised against purified native P1 were tested for their reactivities against the peptides in peptide-specific enzyme-linked immunosorbent assays (ELISAs). Six immu nodominant linear B-cell epitopes were mapped to residues 103 to 137, 189 to 218, 248 to 283, 307 to 331, 384 to 412, and 400 to 437 of the mature P1 protein. When P1 peptides were screened for their reactiviti es with three human convalescent-phase serum specimens, peptides corre sponding to residues 39 to 64, 226 to 253, and 400 to 437 reacted stro ngly with the antisera. Four regions (residues 39 to 64, 226 to 253, 3 39 to 370, and 400 to 437) contained murine T-cell epitopes. Rabbit an tipeptide antisera were tested for their reactivities with the immuniz ing peptides and P1 protein by ELISA and immunoblots. All anti-P1 pept ide antisera except those raised against peptide HIBP1-8 (residues 279 to 312) or HIBP1-8-keyhole limpet hemocyanin conjugate were shown to he specific for their respective immunizing peptides by ELISA, In addi tion, rabbit antisera raised against the synthetic peptides correspond ing to residues 1 to 29, 39 to 64, 103 to 137, 189 to 218, 226 to 253, 248 to 283, 307 to 331, and 400 to 437 of the mature P1 protein recog nized the P1 protein from both typeable and nontypeable isolates. Thes e results suggest that these peptides contain epitopes highly conserve d among typeable and nontypeable strains of H. influenzae. However, no ne of the antipeptide antisera have bactericidal activity, nor were th ey protective against H. influenzae type b in the infant rat model of bacteremia.