Replication of Bovine Parainfluenza-3 Virus in Bovine Alveolar Macrophages : Effects on Phagocytosis and Phagosome-Lysosome Fusion

Abstract

Bovine parainfluenza-3 virus was found to replicate in alveolar macrophages in vitro. Cytopathic changes include spindle cell and giant cell formation, cellular detachment, and diffuse cell lysis progressing to total destruction of the monolayer. Direct immunofluorescent microscopy demonstrated viral antigens in greater than 90% of the cells three days after virus inoculation. Virus titers in culture supernatants increased by 6 a factor of 1.6 X 10 TCID50 by six days post inoculation. Phagocytosis assays showed no statistical differences of glass adherent cells in virus infected and control macrophages. When the number of glass adherent cells available for assay are taken into account (normalization) differences in phagocytic values are significant at 5 and 7 days post inoculation. Phagosomelysosome fusion assays demonstrated marked reduction of fusion activity of virus infected macrophages compared to control macrophages. Fusion values of infected cells were 51% and 53% that of control cells at days 4 and 6, respectively Normalization of these values reduced the fusion rate to 37% of control macrophages. Relatively little is known about the interactions of BPI-3 virus and cultured bovine alveolar macrophages (BAJ1). Rossi et al demonstrated that monocytes derived macrophage cultures exhibited cytopathic effect (CPE) after BPI-3 inoculation. However, it is not known if this virus will undergo productive replication in BAM or what effect it will have upon BAM functions. This study examines the interactions of BPI-3 and cultured BAM with regard to CPE, quantitation of progeny virus, and the quantitation of macrophage processes of phagocytosis and phagosome-lysosome fusion