Inducing and Recalling Immune Memory to AgI/II by Mucosal Immunization

Objectives: Previously it has been shown that intragastric (i.g.) immunization with the recombinant chimeric immunogen, SBR-CTA2/B, comprising the saliva-binding region (SBR) of Streptococcus mutans AgI/II coupled to cholera toxin (CT) A2/B subunit, induces AgI/II-specific salivary IgA and serum IgG antibodies in mice. This study compared the ability of SBR-CTA2/B to recall immune memory after i.g. or intranasal (i.n.) priming and boosting. Methods: Female BALB/c mice (n=4-6/group) were immunized with either 100mg or 25mg of SBR-CTA2/B given i.g. or i.n., respectively. Animals were immunized 3 times at 10-day intervals and rested for 6 months. Booster immunizations were administered by the same route and with the same dose of SBR-CTA2/B as given at priming. Groups received 0, 1, 2, or 3 booster immunizations at 10-day intervals. Saliva and serum were collected 7 days after each boost, and animals were sacrificed on day 10. ELISA was used to determine specific antibodies in serum and saliva. Proportions of memory and activated T and B cells were evaluated by two-color immunofluorescent staining and flow cytometry of single-cell suspensions derived from lymph nodes and spleen. Results: We found that AgI/II- and CT-specific antibody levels detected in serum (IgG) and saliva (IgA) rose with the number of booster immunizations. Higher levels were recorded from mice immunized i.n. compared with those immunized by the i.g. route. Furthermore, greater proportions of memory (CD45RB-low) T cells as well as activated (CD25+/CD69+) B and T cells were found in lymph nodes of mice primed and boosted by i.n. immunization in contrast to mice primed and boosted by the i.g. route. Conclusions: An i.n. priming and boosting regime was found preferable for recalling and activating immune memory cells that are involved in generating salivary IgA antibodies for protection against S. mutans. Supported by NIDCR grant DE06746.