M cell targeting with Aleuria aurantia lectin as a novel approach for oral allergen immunotherapy.

Background: The extent and quality of the immune response to orally applied allergens may critically depend on the precise site of uptake at the intestinal mucosa.

Objective: The aim of this study was to construct allergen vehicles optimized for oral allergen immunotherapy.

Methods: By using a murine model, we examined the immunomodulatory effect of birch pollen proteins entrapped in poly(D,L-lactide-co-glycolide) microspheres, which were specifically targeted to enterocytes or to M cells, in an ongoing T h 2 response. BALB/c mice express different carbohydrates on these 2 cell types. To target the sialylic residues on murine enterocytes, we functionalized microspheres with wheat germ agglutinin (WGA) and, to target alpha-L-fucose on M cells, with a lectin from Aleuria aurantia (AAL), the orange peel mushroom.

Results: Both WGA and AAL functionalization enhanced binding to human Caco2 cells substantially, which express sialylic and, as carcinoma cells, also alpha-L-fucose residues. Different groups of BALB/c mice were first sensitized to birch pollen and subsequently fed with birch pollen-loaded functionalized (WGA microspheres, AAL microspheres) or nonfunctionalized, birch pollen extract-loaded particles. When mice were fed with AAL microspheres, birch pollen-specific IgG2a, but not IgG1 or IgE, increased significantly. As expected, in a 3 H-thymidin assay, their splenocytes proliferated specifically on birch pollen stimulation. Both targeting strategies, using WGA or AAL, induced IL-10 as well as IL-4 production. However, in AAL microsphere-treated mice, IFN-gamma synthesis was significantly increased, which may be responsible for the significant IgG2a production in this group.

Conclusion: Our data indicate that targeting M cells by using AAL-coated allergen vehicles may be a promising strategy for oral allergen immunotherapy.