Age-dependent antibody response in mice and humans following oral influenza immunization

In order to compare the antibody response in serum and secretions from healthy young subjects and the elderly (greater than 60 years), volunteers were immunized with the commercial inactivated influenza virus vaccine, by the usual (parenteral) route or orally. Also, young and old mice (mean age, 20 months) were orally immunized with live influenza virus. The older mice responded with a very slight rise in their serum and respiratory tract antibody levels compared with the young mice but showed no diminution in protection against lethal viral challenge. Elderly volunteers showed only slight serum antibody responses after parenteral immunization compared with the young. Neither group demonstrated a rise in serum antibody following oral immunization. With respect to the secretory IgA (SIgA) antibody response, certain differences were noted between the young and the elderly: the preimmunization levels of antibody to influenza virus were significantly greater in nasal secretions and saliva in the elderly as compared to the young volunteers, and the salivary antibody response was diminished in the elderly. This lack of a salivary antibody response in the elderly was explicable by the inverse relationship between the preimmunization SIgA antibody titers and the response to immunization. Oral immunization led to no more side effects than observed in the placebo control group.