Three different approaches of using overlapping peptides have been compared to analyse the fine specificity of the antibody response to a protective epitope from measles virus (MV) fusion protein, spanning residues 397-420. Anti-peptide antibodies raised in BALB/c, CBA and C57BL/6 mice were shown to react with the homologous peptide and the MV by ELISA. Results from indirect ELISA using 15mer peptides (overlapping by one residue) as solid phase antigens have shown that anti-peptide antibodies from CBA and C57BL/6 mice recognised the same B-cell epitope(s) located within the 398-414 region, whereas BALB/c mice predominantly recognised epitopes located within the 400-417 region. When the 15mer peptides were used as fluid phase antigens in an inhibition ELISA, peptide 405-419 was shown to be the most effective inhibitor in all three strains of mice. Analysis of serum samples by SPOTs ELISA has shown that the region 407-417 was predominantly recognised by BALB/c mice, whereas antibodies from C57BL/6 mice recognised the 408-420 region. No reactivity was observed with serum samples from CBA mice. Although the majority of the identified B-cell epitopes were shown to overlap by the three methods, the identified boundaries of these epitopes differed, suggesting that the size and the mode of peptide presentation affects their antigenicity.

The adjuvanticitity of heat-labile enterotoxin (LT) of Escherichia coli and its non-toxic mutant LTK63 was assessed and compared for intranasal immunization of synthetic peptides. Mice immunized intranasally with LT, or its mutant LTK63, generated strong systemic proliferative and cytotoxic T-cell responses to co-administered synthetic peptides. The wild LT toxin promoted higher peptide-specific proliferative and cytotoxic T-cell responses than the LTK63 mutant. Moreover, the wild-type LT toxin was shown to promote peptide-specific memory CTL responses which were detectable 1 year after intranasal priming. Both LT and LTK63 molecules were shown to be immunogenic, with serum antibody subclasses being predominantly IgG1 and to a lesser extent IgG2a. These findings demonstrate that cellular immune responses to small synthetic peptide antigens administered by the intranasal route can be potentiated with the use of mucosal adjuvants. Moreover, the ability of LT and LTK63 to promote both CD4+ and CD8+ T-cell responses will have relevance to the design and production of future mucosal vaccines.