Serum antibody response induced in mice after oral administration of B subunit of cholera toxin and formalin-killed enterotoxigenic E. coli in enteric coated microparticles

Usually, gastric digestion of antigens administered orally results in a state of immunological unresponsiveness. Humoral immune response has been generated after oral delivery of encapsulated soluble proteins to the gut-associated lymphoid tissue. In this study, we explored the potential of using microcapsules coated with a pH-sensitive enteric coating (methacrylic acid copolymer) for oral immunization for enterotoxigenic Escherichia coli (ETEC). Two different groups of 10 mice received priming and boosting encapsulated doses of: a)B Subunit of cholera toxin, or, b)Formalin-killed ETEC H10407 expressing colonization factor antigen I (CFA/I). Serum IgG antibody was measured on days 0 and 90 by a direct enzyme-linked immunosorbent assay (ELISA). A control group, that received placebo capsules, did not develop a humoral immune response. Positive serum IgG response against B subunit of cholera toxin was induced in the first group (3 mice with titer of 1:10⁵ and 7 with 1:10⁶). In the second group, 8 mice developed a titer of 1:100, one a titer of 1:200 and 1 showed no immune response. In the same group, an anti-CFA/I response was found in 6 mice and anti-LPS was observed in 4, by Western-Blot technique. Our results demonstrated that oral administration of these 2 antigens encapsulated in this new delivery system induced high titers of serum antibody in mice. This method of enteric coated microparticles should be studied further as a potential method for oral immunization for ETEC.