Serum antibody response induced in mice after oral administration of three different antigens of enterotoxigenic Escherichia coli in enteric coated microparticles

Background: Gastric digestion of these antigens plays an important role, decreasing the ability to deliver antigens to the gut-associated lymphoid tissue. To overcome this obstacle, microencapsulated antigens from enterotoxigenic Escherichia coli (ETEC) were evaluated for oral immunization of mice. Methods: Four groups of 10 each received 3 series of 3 doses each of (1) B subunit of cholera toxin (CTB), similar to heat-labile toxin of ETEC, (2) formalin-killed whole cell ETEC H10407 (FK-ETEC), (3) crude preparation of colonization factor antigen I (CFA/I), or (4) placebo. Serum antibody was measured on day 0 and 60 by ELISA. Results: In group 1 a CTB antibody response was induced in all mice, 3 with 1:10⁵ titer and 7 with 1:10⁶. These antibodies neutralized cholera toxin-induced steriodogenesis of Y-1 adrenal cells. In group 2, 8 mice developed a whole H10407 bacteria antibody titer of 1:100, one 1:200 and one showed no immune response. In the same group, an anti-CFA/I response was observed in 6 mice and anti-LPS in 4 mice as determined by Western blot. All mice in group 3 showed > 1:10⁴ anti-CFA/I antibody titer. Group 4 mice did not develop an immune response to any ETEC antigens. Conclusion: Microencapsulation appears to be a suitable approach for oral vaccination against ETEC and Vibrio cholerae.