PASSIVE PROTECTION OF GNOTOBIOTIC CALVES USING MONOCLONAL-ANTIBODIES DIRECTED AT DIFFERENT EPITOPES ON THE FUSION PROTEIN OF BOVINE RESPIRATORY SYNCYTIAL VIRUS

Two neutralizing, fusion-inhibiting bovine monoclonal antibodies (MAbs ; B4 and B13) directed at different epitopes on the fusion protein of respiratory syncytial virus (RSV) protected the lungs of gnotobiotic c alves from RSV infection. The MAbs were administered intratracheally 2 4h before complement-fixing MAb, B1, provided no significant protectio n against infection, and the disease was not exacerbated. Pneumonic co nsolidation and mean virus titer in lung 7 days after challenge were s ignificantly lower in calves given the fusion-inhibiting MAbs than in either control calves or those given MAb B1. The proliferative bronchi olitis with syncytial formation and widespread distribution of RSV ant igen in the lower respiratory tract of the B1-treated and control calv es were indistinguishable and typical of experimental bovine RSV infec tion. Syncytia were markedly absent, and little or no viral antigen wa s detected in either the B4- or B13-treated calves.