Introducing site-specific glycosylation using protein engineering techniques reduces the immunogenicity of ß-lactoglobulin.

To reduce the immunogenicity of ß-lactoglobulin (BLG), we prepared wild-type bovine BLG variant A (wt) and three site-specifically glycosylated BLGs (D28N, D137N/A139S, and P153A), and expressed them in the methylotrophic yeast Pichia pastoris by fusion of the cDNA to the sequence coding for the α-factor signal peptide from Saccharomyces cerevisiae. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis indicated that the glycosylated BLGs were conjugated with a ~4 kDa high-mannose chain. Each glycosylated BLG retained ∼80% of the retinol-binding activity of BLG. Structural analyses by intrinsic fluorescence, CD spectra, and ELISA with monoclonal antibodies indicated that the surface structure was slightly changed by using protein engineering techniques, but that the site-specifically glycosylated BLGs were covered by high-mannose chains without substantial disruption of wt conformation. Antibody responses to the glycosylated BLGs tended to be weaker in BALB/c, C57BL/6, and C3H/He mice. We conclude that site-specific glycosylation is an effective method to reduce the immunogenicity of BLG, and that masking of epitopes by high-mannose chains is effective to reduce immunogenicity.

Reduced T cell response to beta-lactoglobulin by conjugation with acidic oligosaccharides.

We have previously reported that the conjugation of beta-lactoglobulin (beta-LG) with alginic acid oligosaccharide (ALGO) and phosphoryl oligosaccharides reduced the immunogenicity of beta-LG. In addition, those conjugates showed higher thermal stability and improved emulsifying properties than those of native beta-LG. We examine in this study the effect of conjugation on the T cell response. Our results demonstrate that the T cell response was reduced when mice were immunized with the conjugates. The findings obtained from an experiment using overlapping synthetic peptides show that novel epitopes were not generated by conjugation. One of the mechanisms for the reduced T cell response to the conjugates was found to be the reduced susceptibility of the conjugates to processing enzymes for antigen presentation. We further clarify that the beta-LG-ALGO conjugate modulated the immune response to Th1 dominance. We consider that this property of the beta-LG-ALGO conjugate would be effective for preventing food allergy as well as by its reduced immunogenicity. Our observations indicate that the method used in this study could be applied to various protein allergens to achieve reduced allergenicity with multiple improvements in their properties.