Bovine respiratory syncytial virus replicates minimally in bovine alveolar macrophages

The interaction between two different bovine respiratory syncytial virus (BRSV) strains and bovine alveolar macrophages (BAMs) was studied in vitro. Bovine respiratory syncytial virus replicated minimally in BAMs and most of the virus produced remained cell-associated. Approximately 1 out of 1,000 BAMs produced infectious virus, a number that further declined during the 7 days of culture. In contrast, BAMs exposed to bovine parainfluenza 3 virus (PI3V) produced high amounts of infectious virus. The number of BAMs that contained BRSV antigen depended on the antigen load of the inoculum and not on the infectivity of the virus. Antibody mediated enhancement of infection was not detected. It is concluded that bovine alveolar macrophages exhibit a high intrinsic resistance to BRSV, but not to PI3V.