Specificity of Respiratory Secretion Antibody against Influenza Virus

Serum, sputum and nasal secretion neutralizing antibody rises were measured against A2/Taiwan/64, A2/Hong Kong/68 and A/PR8 influenza viruses and parainfluenza type 1 virus in volunteers who had been immunized with A2/Taiwan/64 virus. There was approximately an eightfold rise in sputum, nasal wash and serum antibody to the homologous virus, and no rise to parainfluenza type 1 virus. There was no serum antibody rise to A/PR8 or A2/Hong Kong viruses, but in sputum and nasal washing there was approximately a three- to fourfold rise. Absorption studies with homologous and heterologous virus indicate that the heterologous response is due mainly to cross-reacting antibody. This could mean that secretory IgA is less specific than serum IgG. If these findings are substantiated for other viruses, it is possible that protection against a broad range of viruses may be inducible with fewer vaccines than would be expected on the basis of serologic studies.