INTRANASAL MONOCLONAL IMMUNOGLOBULIN-A AGAINST RESPIRATORY SYNCYTIAL VIRUS PROTECTS AGAINST UPPER AND LOWER RESPIRATORY-TRACT INFECTIONS INMICE

The role of secretory antibody in protection against respiratory syncy tial virus (RSV) infection was examined by using monoclonal immunoglob ulin A (IgA) antibody for intranasal passive immunization of mice. Eig ht anti-RSV IgA hybridomas were produced by fusing myeloma cells with lung lymphocytes from RSV-immunized mice. Five IgA antibodies recogniz ed RSV strains of both the A and the B subgroups, and two of these neu tralized virus in a plaque reduction assay. Monoclonal IgA antibody HN K20, which bound to F glycoprotein, was most effective, reducing plaqu es by 50% at a concentration of 0.1 mu g/ml for both subgroup A and su bgroup B strains. HNK20 also neutralized all of eight clinical isolate s of RSV tested. When delivered intranasally to mice 24 h prior to RSV challenge, HNK20 reduced virus titers in the lungs by nearly 100-fold . Maximal protection occurred at a dose of 0.5 mg/kg of body weight. S ignificant protection against lung infection was seen when the interva l between antibody treatment and challenge was as long as 72 h. HNK20 also decreased virus titers in the nose approximately 10-fold when giv en 1 h, but not 24 h, before challenge. When mice were treated,vith HN K20 intranasally 3 days after challenge, viral titers were reduced in the lungs but not the nose. The results indicate that topical applicat ion of relatively small amounts of monoclonal IgA can protect against both upper and lower respiratory tract infections caused by RSV.