Passive IgA Monoclonal Antibody Is No More Effective Than IgG at Protecting Mice from Mucosal Challenge with Respiratory Syncytial Virus

2,3 Respiratory syncytial virus (RSV) is a mucosally restricted pathogen that can cause severe respiratory disease. Although parenteral administration of sufficient RSV-specific IgG can reduce severity of lower respiratory tract infection in high-risk infants, delivery of antibody by direct airway administration is an attractive alternative. Topical and parenteral adminis- tration of an IgA monoclonal antibody (MAb) specific for the RSV F glycoprotein was compared with an IgG MAb, specific for the same antigenic site, for ability to protect mice against RSV infection. Administration of RSV-specific IgG was more effective in reducing RSV titers in lung (4.6 log10 pfu/g) than IgA MAb (3.6 log10 pfu/g) when given intranasally immediately prior to infection ( ). RSV titers in the nose were reduced only by pro- P= .005 phylactic administration of IgG parenterally. Therefore, topical administration of IgA is no more effective than topically administered IgG and is less effective than systemically admin- istered IgG for protecting against RSV infection.