210 EFFECTS OF INTERFERON-τ ON REPLICATION OF BOVINE VIRAL DIARRHEA VIRUS AND BOVINE HERPESVIRUS-1

Abstract

Bovine viral diarrhea virus (BVDV) and bovine herpesvirus-1 (BHV-1) are the most likely viruses to be associated with abattoir-origin materials used in in vitro embryo production. Further, both viruses are known to associate with zona pellucida-intact embryos after exposure and washing, and limited evidence indicates that developing, transferable embryos are able to inhibit viral replication in adjacent cells. Interferon-τ is known to have anti-BVDV and anti-BHV-1 activities, but it is not known whether interferon-τ which is secreted by developing embryos has the same effects. The objectives of this study were to evaluate the cytotoxicity and anti-viral effect of interferon-τ against a non-cytotoxic high affinity strain of BVDV (SD-1) and against a strain of BHV-1 (Colorado) in cell culture. Madin Darby bovine kidney (MDBK) cells were seeded in 96-well plates and then inoculated with serial dilutions (1:10) beginning with an initial concentration of 0.2 µg of interferon-τ. Cells and interferon were incubated at 37.5°C in 5% CO₂ and air for 24 h prior to addition of virus. Five concentrations of BVDV were added to the wells to give 500, 50, 25, 10 or 5 cell culture infective doses (50% endpoint) per well. Three concentrations of BHV-1-50, 10, and 5 plaque-forming units were evaluated in separate cell cultures. Virus isolation (for BVDV) or plaque assays (for BHV-1) were utilized to determine if the addition of interferon-τ decreased the amount of infective virus. The interferon-τ produced no observable cytotoxicity in MDBK cells in any of the assays. At its three highest concentrations, the interferon-τ significantly decreased the amount of BVDV but it had no significant effect on the amount of BHV-1 in cell cultures. Thus, it is possible that interferon-τ produced by developing embryos might limit or prevent transmission of BVDV to recipients if this virus were to be inadvertently associated with the embryos that are transferred. However, a similar effect is not expected for BHV-1.