CD154 costimulated ovine primary B cells, a cell culture system that supports productive infection by bovine leukemia virus

Bovine leukemia virus (BLV) is closely associated with the development of B -cell leukemia and lymphoma in cattle. BLV infection has also been studied extensively in an in vivo ovine model that provides a unique system for stu dying B-cell leukemogenesis. There is no evidence that BLV can directly inf ect ovine B cells in vitro, and there are no direct data regarding the onco genic potential of the viral Tax transactivator in B cells. Therefore, we d eveloped ovine B-cell culture systems to study the interaction between BLV and its natural target, the B cell. In this study, we used murine CD154 (CD 40 ligand) and gamma -chain-common cytokines to support the growth of B cel ls isolated from ovine lymphoid tissues. Integrated provirus, extrachromoso mal forms, and viral transcripts were detected in BLV-exposed populations o f immature, rapidly dividing surface immunoglobulin M-positive B cells from sheep ileal Peyer's patches and also in activated mature B cells isolated from blood. Conclusive evidence of direct B-cell infection by BLV was obtai ned through the use of cloned B cells derived from sheep jejunal Peyer's pa tches. Finally, inoculation of sheep with BLV-infected cultures proved that infectious virus was shed from in vitro-infected B cells. Collectively, th ese data confirm that a variety of ovine B-cell populations can support pro ductive infection by BLV. The development of ovine B-cell cultures permissi ve for BLV infection provides a controlled system for investigating B-cell leukemogenic processes and the pathogenesis of BLV infection.