Feline leukaemia viruses (FeLVs) have long been known to be associated with induction of proliferative and anti-proliferative diseases of domestic cats. Strains of FeLV have been recognized which specifically induce
lymphosarcoma,
aplastic anaemia, myelodysplastic anaemia, and, recently,
feline AIDS (
acquired immune deficiency syndrome), a naturally occurring immunosuppressive syndrome strikingly similar to human
AIDS which is lethal in 100% of inoculated and viraemic specific-pathogen-free (SPF) cats. Here, we have analysed FeLV
DNA in tissues of 22 SPF cats that had been inoculated with the
feline AIDS strain (FeLV-
FAIDS) and we find two classes of
viral DNA--a monotypic common form which is detectable in bone marrow regardless of disease state, and variant forms, recognizable by restriction site differences, whose appearance correlates with onset of disease symptoms and persists throughout the course of the disease. FeLV-
FAIDS variant
DNA is detected at high concentration (10-50 copies per cell) and principally as unintegrated
viral DNA (UVD) in bone marrow of cats with
feline AIDS. In marked contrast high levels of UVD were not present in cats in the terminal-stages of T-cell
lymphosarcoma,
aplastic anaemia, or myelodysplastic anaemia induced by other FeLV strains. These results parallel recent observations in humans, where high levels of UVD were sometimes found in cells derived from
AIDS patients infected with human T-lymphotropic virus type III (HTLV-III)/lymph-
adenopathy-associated virus (LAV), and suggest that persistence of unintegrated variant
viral DNA is a crucial
indicator of retrovirus-induced cytopathic disease syndromes such as
AIDS.