Passive IgA monoclonal antibody is no more effective than IgG at protecting mice from mucosal challenge with respiratory syncytial virus

Respiratory syncytial virus (RSV) is a mucosally restricted pathogen that c an 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 admin istration is an attractive alternative. Topical and parenteral administrati on 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 abi lity to protect mice against RSV infection. Administration of RSV-specific IgG was more effective in reducing RSV titers in lung (4.6 log(10) pfu/g) t han IgA MAb (3.6 log(10) pfu/g) when given intranasally immediately prior t o infection (P = .005), RSV titers in the nose were reduced only by prophyl actic administration of IgG parenterally, Therefore, topical administration of IgA is no more effective than topically administered IgG and is less ef fective than systemically administered IgG for protecting against RSV infec tion.