Antigen coupled with Lewis-x trisaccharides elicits potent immune responses in mice

Background: Glycoproteins containing Lewis-x (Le^x) trisaccharides are often associated with the host's adaptive T_H2-type immunity, but the mechanisms underlying the T_H2-biased response are at present unclear. Objective: The modulatory effect of Le^x or its glycoconjugates on IgE/T_H2 responses was investigated. Methods: The levels of serum antibodies and cytokines were analyzed by means of ELISA, RT-PCR, or both. Results: In C3H mice Le^x coupled with BSA (Le^x-BSA) elicited higher levels of specific IgE and IgG1, but not IgG2a, which were associated with increased levels of splenic T_H2 cytokines when compared with those seen in BSA-sensitized mice. In BALB/c mice sensitized with Le^x-BSA or Le^x mixed with ovalbumin, significantly increased levels of specific IgE and IgG2a antibodies were found concomitant with reduced levels of serum IL-12p70. These effects were attenuated in IL-12-deficient BALB/c mice. Le^x and an isomer, Le^y, but not other isomers, inhibited the production of LPS-induced IL-12p70, associated with a significant reduction of nuclear NF-κB, in bone marrow-derived dendritic cells from BALB/c mice, suggesting that Le^x-induced suppression of IL-12p70 results in an enhanced T_H2 response. The addition of mannan, a known ligand for dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin, abrogated the suppressive effect of Le^x trisaccharides. Conclusion: These results provide evidence for a potential role of Le^x trisaccharides in shaping the immune responses through, at least in part, its suppressive effect on IL-12p70 production. Considering the relative ubiquity of glycoproteins with Le^x or similar oligosaccharides, including plant-derived (or food-derived) allergens, these findings might have a broad implication. Clinical implications: The adjuvant activity of Le^x trisaccharides might aid in vaccine design and might be important in determining the allergenicity of proteins containing this or other similar structures.