Border disease virus antigens in lymphocyte subpopulations in the peripheral blood of persistently infected sheep

Antigens of bovine respiratory syncytial virus in peripheral blood lymphocytes of experimentally infected lambs

Eight lambs were experimentally infected with bovine respiratory syncytial virus (RSV) and the distribution of viral antigen in lymphocyte subpopulations studied by flow cytometry. Experimental infection with bovine RSV was characterised by significant changes in lymphocyte subpopulations. Infection was followed by a significant (P <0.001) reduction in the number of cells expressing the OvCD5 epitope (T cells), due to a fall in the number of cells expressing the OvCD4 epitope (helper) and those expressing the OvWC1 epitope (gamma/delta) 3-7 days post-inoculation. There was a significant increase in the number of OvCD5+ cells expressing the OvCD8 epitope (cytotoxic/suppressor) later. Flow cytometric analysis with bovine RSV-specific monoclonal antibodies revealed that viral antigens were present in all lymphocyte subpopulations but the main targets were T cells in general and OvCD4+ cells in particular. Challenge of primed lambs with bovine RSV had similar effects over a shorter period, followed by significant rises in the number of OvCD45+ (B) cells and OvCD5+ (T cells). Viral antigens were also present in lymphocytes subsets following challenge.

Replication of bovine respiratory syncytial virus in ovine peripheral blood lymphocytes and monocytes in vitro

Adherent and non-adherent mononuclear cells obtained from the peripheral blood of normal lambs supported the replication of bovine respiratory syncytial virus in vitro. Sequential treatment of monocytes with phorbol ester acetate (PMA) enhanced their ability to support viral replication. After exposure in vitro for 24 h, viral antigens were present in 47 +/- 4.5% of monocytes and 32 +/- 3% of lymphocytes. Treatment of monocytes with PMA resulted in the increase of the proportion of cells expressing viral antigen and in the titre of infectious virus.

An immunohistochemical study of the distribution of border disease virus in persistently infected sheep

Three seronegative sheep persistently infected with Border disease virus and six seropositive, non-viraemic sheep were examined for the cellular distribution of the agent. These animals originated from a closed flock which had been kept in an isolation facility for 5 years. They were killed and immediately necropsied. There were no gross abnormalities other than reduced body weight of the persistently infected sheep. Two samples of each major organ were collected. The first sample was fixed by immersion in formalin and processed for histological examination, which showed no lesions unequivocally attributable to the viral infection. The second sample was snap-frozen for immunohistochemical examination. This revealed viral antigen in all organs of the persistently infected, but in none of the seropositive animals. The infected cells included smooth muscle cells of hollow organs and blood vessels, epithelial cells of the alimentary tract and urogenital organs, lymphocytes in lymphoid organs, endocrine cells, neurons and glial cell.