Abstract
Parenteral immunization of BALB/c mice at 3 months of age with inactivated influenza virus vaccine elicited a haemagglutinin (HA)-specific serum IgG antibody response. The magnitude of this response declined with advancing age at the time of vaccination. By contrast, HA-specific IgA and IgG antibody levels observed in lung lavage fluids of mice immunized at 1 and 2 years of age were comparable to those of 5 month old mice when inactivated influenza virus vaccine was administered intragastrically. The secretory immune response was not fully developed in the first 3 weeks of life. However, the HA-specific IgA and IgG responses to oral vaccination in sera were reduced in 1 or 2 year old mice when compared to 5 month old mice. These data demonstrated the preservation of the virus-specific secretory IgA response in the pulmonary fluids of aged mice after oral vaccination with inactivated influenza virus vaccine. An age-dependent difference of systemic and mucosal immunity was evident in orally immunized mice.