A non-toxic lectin for antigen delivery of plant-based mucosal vaccines

RicinB, the non-toxic galactose/N-acetylgalactosamine-binding subunit of ricin, was fused to a model antigen, green fluorescent protein (GFP), and expressed in tobacco plants and hairy root cultures to test for utility in mucosal vaccine delivery/adjuvancy. The fusion protein retained both GFP fluorescence and galactose/galactosamine-binding activity. Intranasal immunization of mice with galactosamine-affinity purified ricinB:GFP recovered from tobacco root cultures triggered significant increases in GFP-specific serum IgGs. This strong humoral response was comparable to that observed following GFP immunization with cholera toxin adjuvant. GFP at the same concentrations but without an adjuvant was non-immunogenic. Induction of higher levels of IgG(1) than IgG(2a) following ricinB:GFP immunization suggested the presence of a Th2 response. Serum and fecal anti-GFP IgA were also induced by immunization with ricinB:GFP. Our data suggest that ricinB can be used as an adjuvant and antigen carrier to the mucosa and is efficient in eliciting systemic and mucosal immune responses.