Submitted to: Immunology Research Workshop
Publication Type: Abstract Only
Publication Acceptance Date: September 16, 2003
Publication Date: N/A
Technical Abstract: While bovine viral diarrhea viruses (BVDV) are highly lymphotrophic in vivo, in vitro they are studied in epithelial cells. BVDV are classified as cytopathic (cp) or noncytopathic (ncp) based on their activity in cultured epithelial cells. This does not correlate with virulence in acute infections, as the most highly virulent BVDV are ncp. The purpose of this study was to determine if virulence in vivo could be correlated with growth characteristics in cultured lymphoid cells. A BL-3 cell line (derived from a B cell lymphosarcoma) free of BVDV and bovine leukemia virus was used. Cultures were infected with the highly virulent (hv) ncp BVDV2 strain 1373, the low virulent (lv) ncp BVDV2 strain 28508-5 or the lv cp BVDV2 strain 296c. Cell growth, proliferative state, ratio of live to dead cells and virus replication were monitored. Cell morphology was observed by light and electron microscopy. No significant differences were seen between noninfected cells and 28508-5 infected cells. Cytopathic effect (cpe), as defined by cell death, was observed in cells infected with 1373 and 296c. However, the cpe observed with the two strains were different. The cpe associated with 296c infection was apparent within the first 48 hours after infection and was associated with the condensation and fragmentation of most nuclei. Cpe associated with 1373 was not apparent until 96 hours after infection. Cells were non-proliferative but nuclei appeared morphologically normal. The cell cytoplasm became less dense and disorganization of mitochondria was observed. Nuclear condensation and fragmentation became common only in cells in the late stages of cpe. These results suggests that different mechanisms are involved in the cell death associated with lv cp strains and hv ncp virulent strains. Based on these findings BVDV may be grouped into three biotypes, cp (based on cpe in epithelial cells and cultured lymphoid cells within the first 48 hours after infection), ncp (based on lack of cpe in both epithelial and lymphoid cells lines and lymphocidal (based on cell death in lymphoid cell lines 96 hrs post infection).