Effects of Ag/adjuvant ratio on the systemic and mucosal antibody responses of BALB/c mice immunized intradermally with CfaEB, a minor-major subunit fusion of the enterotoxigenic E. coli CFA/I fimbriae, and LT(R192G/L211A) (VAC9P.1104)

Abstract

Listen

Translate article

Abstract The ratio of Ag/adjuvant in a vaccine can modulate the immune response as well as side effects. We studied the effects of different doses of CfaEB, a minor-major subunit fusion of the enterotoxigenic E. coli (ETEC) CFA/I fimbriae, given ID with the adjuvant LT(R192G/L211A), or dmLT, an attenuated form of the ETEC heat-labile enterotoxin. BALB/c mice were immunized with 0.1, 1, 10 or 100 mg of CfaEB alone or with 10 or 100 ng of dmLT on days 0 and 21. Sera from days 21 and 28 were tested by ELISA and hemagglutination inhibition assay. Mucosal responses were assessed in day 28 fecal pellets. Serum anti-CfaE IgG Ab titers directly correlated with the dose in groups receiving no adjuvant but the highest titers were seen in the two groups receiving 10 mg of CfaEB plus 10 or 100 ng dmLT. A similar pattern was observed with serum anti-CfaE IgA responses, although 100 mg of CfaEB plus 10 or 100 ng of adjuvant elicited the highest levels. Groups receiving 10 or 100 mg of CfaEB plus 100 ng dmLT manifested the highest functional Ab titers. The adjuvant at either dose was required to elicit a strong fecal anti-CfaE IgA response, and it directly correlated with CfaEB dose in the adjuvanted groups. Our results demonstrate the importance of dmLT in promoting mucosal Ab responses to our vaccine when given by the ID route. Since optimal mucosal vs. systemic functional Ab responses are elicited by different Ag/adjuvant ratios, the ratio should be selected to elicit the desired immune response.