The B cell epitope of paramyosin recognized by a protective monoclonal IgE antibody to Schistosoma japonicum

Passive immunization of mice with a monoclonal IgE antibody to Schistosoma japonicum (SJ18ε.1) induces significant protection to a challenge infection and the target molecule of SJ18ε.1 is paramyosin. In the present study, we demonstrate the B cell epitope of paramyosin recognized by SJ18ε.1 by using a series of deletion mutants expressed in Escherichia coli. SJ18ε.1 reacted with the recombinant paramyosin containing 113 amino acids (Glu 301-Ala 413) but not with a shorter peptide (Glu 301-Asp 343). Further epitope mapping carried out by a multi-pin system using heptameric peptides synthesized sequentially from 71 amino acids of paramyosin (Asp 343-Ala 413) demonstrated significant binding of SJ18ε.1 to the sequence, 359Ile-Arg-Arg-Ala 362. Replacement set analysis of the pentameric peptide, 358Leu-Ile-Arg-Arg-Ala 362, revealed that replacement of each residue with a hydrophobic or hydrophilic amino acid did not inhibit binding of SJ18ε.1, whereas replacement of positively charged Arg, or hydrophobic Ala with a negatively charged amino acid, Glu, showed reduction in binding of the antibody. Moreover, replacement of each amino acid including Arg with a positively charged amino acid, Lys, resulted in a drastic loss of the binding, indicating that binding of the antibody was markedly affected by the change of charges of the peptide as well as by the conformational alteration. The target epitope of SJ18ε.1 was common among paramyosins of S. mansoni, Taenia solium and Echinococcus granulosus but not among nematode paramyosins, suggesting that the epitope is specific for platyhelminthes.