Induction of mucosal and systemic immune responses by intranasal immunization using recombinant cholera toxin B subunit as an adjuvant

Intranasal (i.n.) immunization with Streptococcus mutans surface protein AgI/II mixed with cholera toxin B subunit (CTB) containing a trace amount of cholera toxin (CT) induces strong immune responses in mucosal and systemic sites, but whether pure CTB alone has an adjuvant effect has been questioned To determine the adjuvant effect of recombinant (r) CTB, mice were immunized with 10 mu g of AgI/II either mixed with ol conjugated to 5 mu g of rCTB, and antibody responses in saliva, nasal wash, gut wash, vaginal wash, and serum were assayed by ELISA. The results showed that AgI/II either mixed with or conjugated to rCTB could induce both mucosal IgA and systemic IgG antibodies to higher levels than in mice similarly immunized with AgI/II alone. Some responses, especially serum IgG antibodies, were enhanced by adding 5 mu g of CT to the immunogen, whereas overall mice immunized with AgI/II mixed with CTB contaminated with CT tended to generate the strongest mucosal IgA and serum Ige responses to AgI/II. However, rCTB used as an adjuvant induced lower antibody responses against itself than CTB intentionally or inadvertently mixed with CT. These results show that rCTB can serve as an adjuvant for protein immunogens administered by the i.n. route. (C) 1997 Elsevier Science Ltd. All rights reserved.