Intragastric and intraperitoneal administration of Cry1Ac protoxin from Bacillus thuringiensis induces systemic and mucosal antibody responses in mice

The spore-forming soil bacterium Bacillus thuringiensis produces parasporal inclusion bodies composed by delta-endotoxins also known as Cry proteins, whose resistance to proteolysis, stability in highly alkaline pH and innocuity to vertebrates make them an interesting candidate to carrier of relevant epitopes in vaccines. The purpose of this study was to determine the mucosal and systemic immunogenicity in mice of CrylAc protoxin from B. thuringiensis HD73. Crystalline and soluble forms of the protoxin were administered by intraperitoneal or intragastric route and anti-CrylAc antibodies of the major isotypes were determined in serum and intestinal fluids. The two forms of CrylAc protoxin administered by intraperitoneal route induced a high systemic antibody response, however, only soluble CrylAc induced a mucosal response via intragastric. Serum antibody levels were higher than those induced by cholera toxin. Systemic immune responses were attained with doses of soluble CrylAc ranging from 0.1 to 100 mu g by both routes, and the maximal effect was obtained with the highest doses. High anti-CrylAc IgG antibody levels were detected in the large and small intestine fluids from mice receiving the antigen via IF. These data indicate that CrylAc is a potent systemic and mucosal immunogen.