Enhanced protection against respiratory influenza A infection in mice by liposome-encapsulated antibody.

Liposome-mediated passive immunity was evaluated for its efficacy in the prophylaxis and treatment of influenza A/PR/8 virus infection in mice. A mouse LD50 protection model was developed using a polyclonal anti-influenza A antibody which demonstrated strong reactivity against the mouse-adapted virus in a fluorogenic enzyme immunoassay and in an in vitro plaque assay. Using liposomes as an antibody carrier system, the delivery of antibody to the lungs was optimized. For mice given the antiviral antibody intranasally 24 h prior to challenge with 10 LD50 of mouse-adapted influenza A/PR/8 virus, the survival rate at 14 days post-challenge was 60%. However, when mice were given antibody encapsulated within liposomes, the survival rate increased to 100%. In the treatment of mice preinfected with 10 LD50 of the virus, mice were fully protected (100% survival rate) when treated within 8 hr post-infection with free unencapsulated antibody, or within 12 hr with liposome-encapsulated antibody. It is postulated that the improved therapeutic and prophylactic efficacies of the antiviral antibody may be attributed to enhanced delivery as well as retention of antibody molecules in the lungs when liposomes are used as antibody carrier system.