In vitro erythrocytopathic activity of an aplastic anemia-inducing feline retrovirus

Although feline leukemia viruses (FeLV) cause a spectrum of proliferative and anti-proliferative diseases in vivo, in vitro studies demonstrating cell lineage-specific pathogenic properties of feline retroviruses have been rare. We describe here an efficient in vitro system that demonstrates the selective cytopathic effect of a molecularly cloned anemogenic FeLV (FeLV-Sarma-subgroup C; FSC) on erythroid progenitor cells. Forty-eight-hour coculture of normal feline bone marrow mononuclear cells with an underlayer of FSC-infected feline fibroblasts (FeF) resulted in infection of 60% to 90% of marrow mononuclear cells and pronounced depletion of early erythroid progenitor cells (BFUe). The dramatic depletion of BFUe was specific for FSC and did not occur in marrow cells infected with a molecularly cloned nonanemogenic subgroup A FeLV (FeLV 1161E; F6A). The ablation of BFUe by FSC in vitro paralleled both the decrease in BFUe and the induction of aplastic anemia in vivo. This combination of marrow cell infection by coculture and colony-forming unit (CFU) assessment by methylcellulose assay provides a reliable in vitro technique for studies of mechanisms involved in retrovirus-induced marrow aplasias.