Persistence of serum and salivary antibody responses after oral immunization with a bacterial protein antigen genetically linked to the A2/B subunits of cholera toxin.

Primary oral immunization of mice with a bacterial protein antigen genetically coupled to the A2 and B subunits of cholera toxin induced specific secretory immunoglobulin A and serum immunoglobulin G antibodies that persisted at substantial levels for at least 11 months. A subsequent single booster immunization did not further enhance the antibody responses. Long-term antibody persistence may be especially important in infections caused by common pathogens for which continuous immunity would be advantageous.