2. Materials and methods
2.1. Peptide synthesis
The peptide antigens for immunoassays and the peptide
immunogens for vaccines were produced by synthesis on
a solid-phase support using an Applied Biosystems Peptide
Synthesiser Model 430A, and Fmoc protection for
the -NH2 terminus and side chain protecting groups of
trifunctional amino acids. Peptides having combinatorial
library Th epitopes were prepared by providing a mixture
of the desired amino acids at the specified positions.
Completed peptides were cleaved from the solid support
and side chain protecting groups removed by 90% trifluoroacetic
acid. Synthetic peptide preparations, except for the
library immunogens, were characterised for correct composition
by matrix-assisted laser desorption time-of-flight
mass spectrometry using a PerSeptive Biosystems/Vestec
LaserTec Benchtop 11 mass spectrometer, and by reverse
phase HPLC. The library immunogen for the vaccine was
characterised by size exclusion chromatography to a speci-
fication that requires 90% of the integrated area to exceed
a mass threshold limit value, and by Edman degradation
for N-terminal amino acid analysis. Liquid phase cyclisation
of the peptide immunogens was accomplished by
dissolving the peptides in water at 0.8 mg/ml, pH 3, adding
DMSO to 1% (v/v) and adjusting to pH 7.5 with NH4OH.
The solution was incubated at ambient temperature in air
and checked daily for 3 days by colorimetric assay using
Ellman’s reagent until disulphide bond formation was at
least 90% complete.