The effects of a flanking sequence on the immune response to a B and a T cell epitope from the fusion protein of measles virus.

A region of the fusion protein of measles virus (residues 240 to 252) was predicted to contain a B and a T epitope. A synthetic peptide representing this sequence was shown to induce both T and B cell reactivity in several inbred strains of mice, but the responses were clearly major histocompatibility complex-restricted. Elongation of this peptide by six residues at the C terminus on the basis of predictions for B cell epitopes resulted not only in increased peptide immunogenicity in some strains of mice but also produced strain-related positive and negative effects on the recognition of the peptide. BALB/c and SWR mice were non-responders to the short version of the peptide but responded well to the elongated form. On the other hand, the injection of the elongated peptide into C57BL/6 mice resulted in a loss of both B and T cell responsiveness seen with the short version. These results indicate the importance of flanking sequences on the immunogenicity and antigenicity of synthetic B and T cell epitopes and highlight the necessity to determine the most appropriate size of peptide to be used as an immunogen.