Interaction of bluetongue virus with bovine lymphocytes

Freshly isolated, and established, cultures of bovine peripheral blood mononuclear leukocytes (PBMLs) were exposed to bluetongue virus (BTV) for the purpose of defining potential lymphotropism. PBML cultures were established in the presence of interleukin 2 (IL-2) and mitogen and maintained either as bulk culture or were cloned prior to infectivity studies. All cultures appeared to be of the T cell phenotype based on the following characteristics: binding of T lymphocyte-specific lectins (i.e. peanut agglutinin and Helix pomatia), rosetting of sheep erythrocytes, binding of a putative pan-T monoclonal antibody, and absence of surface immunoglobulin (Ig). T lymphocyte cultures were further characterized by their ability to elicit lectin-dependent cellular cytotoxicity (LDCC). Exposure of established lymphocyte cultures to BTV resulted in productive cytopathic and non-cytopathic infections. Non-cytopathic productive infections were observed in LDCC-negative cultures whereas cytopathic and non-cytopathic infections were observed in LDCC-positive cultures. Exposure of freshly isolated PBMLs to BTV resulted in minimal virus replication; addition of mitogen and IL-2 to such cultures did not augment virus replication. Addition of mitogen and IL-2 induced negligible blast transformation, whereas PBML viability was minimally affected. These studies establish a tropism of BTV for bovine T lymphocytes with virus replication being limited to those cells undergoing blastogenesis. Establishment of infected lymphocyte cultures, without loss of culture viability, suggest such an interaction may contribute to the long term viraemias associated with BTV infection of cattle.