Effect of infectious bovine rhinotracheitis virus infection of calves on cell populations recovered by lung lavage.

Calves were challenge exposed with infectious bovine rhinotracheitis (IBR) virus, and experiments were carried out to determine the presence of virus in the lungs, virus or viral antigen in alveolar macrophages, and alterations in immune functions of alveolar macrophages. In experiment 1, calves were challenge exposed intranasally with IBR virus. Although clinical signs of IBR occurred in all challenge-exposed calves, there was minimal evidence of virus or viral antigen in cells lavaged from their lungs, and macrophage Fc- and complement-receptor activities, phagocytic activity, and ability to mediate antibody-dependent cell cytotoxicity were unaltered. In experiment 2, calves were challenge exposed intranasally or by aerosol with IBR virus strains Colorado-1 and 108, and samples were collected 4 and 6 days after challenge exposure. Virus was isolated from the lungs, and pathologic lesions of greater severity occurred in those calves challenge exposed by aerosol. Less than 0.1% of lavaged cells from challenge-exposed calves produced infectious centers on susceptible cell monolayers. In 1 sample of lavaged cells, approximately 5% of the cells, mainly macrophages, had viral antigen in the cytoplasm, as detected by immunofluorescence. Because of the small proportion of macrophages that appeared to become infected after challenge exposure of calves with IBR virus, it is believed that the effect of IBR virus in predisposing calves to pneumonic pasteurellosis is an indirect, rather than a direct, manifestation of viral infection of macrophages.