Antibody responses and protection in mice immunized orally against influenza virus.

Antibody responses and protection were studied in BALB/c mice immunized orally with formalin-inactivated influenza viruses (A/PR/8/34) combined with cholera toxin B subunit as adjuvant. Influenza virus-specific IgA as well as IgG antibody responses were induced in the mice, depending on the oral dosage frequency. The oral immunization by multiple doses resulted in reduction of viral replication in the nose and prevention of development of infection in the lung after intranasal (i.n.) challenge. The protective effect in the nose was thought to be related to the nasal IgA antibody response. The oral immunization was, however, less efficient for induction of the IgA antibody response and protection in the nose, compared with an i.n. immunization. The oral immunization following subcutaneous priming led to the complete protection in the nose, accompanied-by a prompt local IgA antibody response.