Investigation of the cellular tropism of bovine immunodeficiency-like virus

The specific viral cell receptor(s) by which many lentiviruses target cells for infection are still largely unresolved. In lentiviral infections of ungulate animals the viruses show a tropism for cells of the monocyte/macrophage lineage, while in species where lentiviral infection causes immunodeficiency disease, there is also a tropism for T-lymphocytes. The real pathogenic mechanisms of BIV in cattle still remain ill-defined since its original isolation from an animal showing transient leucocytosis, lymphadenopathy, lesions in the central nervous system and progressive weakness and emaciation. These symptoms are similar to the early events observed in several of the immunosuppressive lentiviral infections although little is known about the long-term effects of BIV infections and an AIDS-like disease has not yet been associated with BIV infections. BIV, like other lentiviruses, replicates in cells of the immune system and has been isolated from peripheral blood mononuclear cells, lymph nodes, liver and spleen of infected animals. Examples of BIV being associated with immune defects include a diminution in lymphocyte blastogenesis of mitogens and infection and dysfunction of monocytes, but not T-cells. Our own studies have shown that although BIV seems to have no effect on leucocyte populations, there is a significant depletion in CD4 super(+) cell staining within various lymph nodes at the time of peak viraemia. Whether this is a direct result of BIV infection of these cells or an indirection interaction of CD4 super(+) cells with an infected cell-type has not been resolved. We have undertaken a study of the susceptibility of isolated cell populations to infection with BIV using PCR, Southern blot and reverse transcriptase assays.