Comparative immunological properties of enantiomeric peptides

Summary

The immunogenicity of a peptide composed of only d-amino acids is compared with that of the corresponding l-peptide enantiomer. Following three administrations of 100 μg of individual peptide formulated with different adjuvants (Freund's complete adjuvant, QS21, or alum) to BALB/c mice, guinea pigs and rabbits, the l-peptide elicited strong l-peptide-specific IgG antibody responses in all formulations, whereas the d-peptide-induced d-peptide-specific IgG antibodies in the Freund's complete adjuvant and QS21 formulations, but was nonimmunogenic in the alum formulation. Mouse T-cell lines induced by the d-peptide formulated in Freund's complete adjuvant were found to express significant amounts of IL-2 when they were stimulated by the d-peptide. When an equal amount of both enantiomers was mixed and administered in Freund's complete adjuvant, only an l-peptide-specific IgG antibody response was observed. These results suggest that (i) d-peptide is immunogenic when strong adjuvant is provided; (ii) the immune system has preferential recognition of l-amino acid peptide; and (iii) the d-peptide can elicit d-peptide-specific T-cell responses.