Mucosal immunization of BALB/c mice using enterotoxigenic Escherichia coli colonization factors CFA/I and CS6 administered with and without a mutant heat-labile enterotoxin.

Mice (BALB/c) were intranasally (IN) and intragastrically (IG) administered the ETEC colonization factors (CF), CFA/I and CS6, with and without the R192G mutant heat-labile enterotoxin (mLT), and immunogenicity and efficacy measured. The IN administration of CFA/I to mice induced strong serum and fecal IgG and IgA responses. The IG administration of CFA/I to mice induced serum IgG and fecal IgA responses, but only when mLT was co-administered with CFA/I were serum IgA titers detected. The IN administration of CS6 to mice induced serum IgG antibodies, and mLT, when co-administered with CS6, enhanced the serum IgG response. Only when the mLT was co-administered with CS6, were serum and fecal IgA responses detected. The IG administration of CS6 plus mLT induced serum IgG and fecal IgA responses. Partial protection against lethal challenge with ETEC strain H10407 was seen in the mice IN administered the CFA/I plus mLT (P<0.01), and H10407 was cleared from the lungs of CFA/I plus mLT-immunized mice at a significantly greater rate than from the control mice (P<0.05). CFA/I and CS6 administered IN and IG induced mixed Th1/Th2 immune responses with the Th2 type being predominant as evidenced by IgG1>IgG2a. The administration of colonization factors to mice, particularly by the IN route, potentially serves as a useful way to measure the serum and mucosal immune responses to these antigens prior to their use in volunteers.