Fig 4.

The A subunit acts as a mucosal adjuvant for coadministered antigens. Groups of 6 BALB/c mice each were immunized intranasally three times at weekly intervals with TT alone or in combination with one of the test adjuvants. Serum and mucosal anti-TT antibody responses were evaluated by ELISA 1 week after the final dose. The test adjuvants included B, A, A1, dmLT, and A plus B. Both group mean OD values (A) and medians of individual antibody responses (B to F) demonstrate that A and A1 can function as adjuvants and elicit greater responses than the B subunit or no adjuvant but lower responses than dmLT or A plus B for serum IgG (B), IgG1 (C), and IgG2a (D). Mucosal anti-TT IgA responses were detected in BAL fluid (E) and fecal pellets (F) of immunized mice. Strikingly, induction levels of IgA antibodies were similar between A-, A1-, dmLT-, and A-plus-B-adjuvanted groups, suggesting that induction of mucosal IgA against coadministered antigens is A subunit dependent and that very low levels of residual enzymatic activity are both necessary and sufficient for adjuvanticity. Individual animal results are represented as individual points and group medians in the bar graphs. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ns, not significant compared to no-adjuvant (TT only) controls unless otherwise indicated.