Modulation of the specific allergic response by mite allergens encapsulated into liposomes.

Liposomes are non toxic and biodegradable lipid vesicles, which are safe and effective adjuvants to induce Th1-skewed immune response. Therefore, the encapsulation of allergens into liposomes could be an attractive alternative for specific allergy immunotherapy. Previously, we obtained DPPC iposomes encapsulating purified allergens from Dermatophagoides siboney, with suitable stability and extremely reduced allergenicity. In this study, Balb/c mice were immunized with allergens ncapsulated into liposomes (LP) and the induced immune response was evaluated in comparison with allergens dissolved in PBS (PBSA) or adsorbed in Alum (AL). The use of Alum or Liposomes induced a strong allergen specific IgG response. However, total IgE serum levels in the AL group were very high, while levels found in LP group were not significantly different from the control group receiving only PBS. The IgG2a/IgG1 subclass ratio was raised in the LP group. Allergen specific IgE, as measured by PCA assay, was similar for LP and PBSA groups, and approximately the half of the reaction size found in AL group. After allergen challenge by inhalation route, peripheral blood and airway eosinophil counts increased significantly in AL, but not in LP group. Additionally, histopathological analysis of lung tissue sections obtained from challenged mice indicated a reduced cellular infiltration in mice immunized with liposomes. These results support the potential use of liposomal formulations for allergen vaccines.

Model peptides mimic the structure and function of the N-terminus of the pore-forming toxin sticholysin II.

To investigate the role of the N-terminal region in the lytic mechanism of the pore-forming toxin sticholysin II (St II), we studied the conformational and functional properties of peptides encompassing the first 30 residues of the protein. Peptides containing residues 1-30 (P1-30) and 11-30 (P11-30) were synthesized and their conformational properties were examined in aqueous solution as a function of peptide concentration, pH, ionic strength, and addition of the secondary structure-inducing solvent trifluoroethanol (TFE). CD spectra showed that increasing concentration, pH, and ionic strength led to aggregation of P1-30; as a consequence, the peptide acquired beta-sheet conformation. In contrast, P11-30 exhibited practically no conformational changes under the same conditions, remaining essentially structureless. Moreover, this peptide did not undergo aggregation. These differences clearly point to the modulating effect of the first 10 hydrophobic residues on the peptides aggregation and conformational properties. In TFE both the first ten hydrophobic peptides acquired alpha-helical conformation, albeit to a different extent, P11-30 displayed lower alpha-helical content. P1-30 presented a larger fraction of residues in alpha-helical conformation in TFE than that found in St II's crystal structure for that portion of the protein. Since TFE mimics the membrane environment, such increase in helical content could also occur upon toxin binding to membranes and represent a step in the mechanism of pore formation. The peptides conformational properties correlated well with their functional behavior. Thus, P1-30 exhibited much higher hemolytic activity than P11-30. In addition, P11-30 was able to block the toxin's hemolytic activity. The size of pores formed in red blood cells by P1-30 was estimated by measuring the permeability to PEGs of different molecular mass. The pore radius (0.95 +/- 0.01 nm) was very similar to that of the pore formed by the toxin. The results demonstrate that the synthetic peptide P1-30 is a good model of St II conformation and function and emphasize the contribution of the toxin's N-terminal region, and, in particular, the hydrophobic residues 1-10 to pore formation.