Specificity of the Local Secretory Antibody to Influenza a Virus Infection

In animals immunization against influenza A virus via the respiratory tract provides protection against homologous virus challenge that is superior to immunization via a parenteral route although equivalent levels of specific serum antibodies are induced by both procedures (1–3). The evidence for superiority of local immunization in man is less definitive but several studies have shown at least comparable, if not superior, effectiveness of immunization with viral antigen via the respiratory route compared with the parenteral route (4–6). With a series of other respiratory tract viruses the local production of neutralizing antibody of the IgA subclass in the respiratory tract appears to be related to resistance to infection and disease in man; however, a definitive demonstration of the biologic role of local IgA antibody in resistance to influenzal disease has not yet been achieved (7–9). Recently, evidence was presented which suggested the respiratory tract possesses a local cell-mediated immune mechanism which is distinct from systemic cell-mediated immunity (10). Still lacking with the cellular system, as with the secretory immunoglobulin system, is clear evidence of a role in protection against influenzal disease.