Canine large granular lymphocyte leukemia and its derived cell line produce infectious retroviral particles

We describe a case of large granular lymphocyte (LGL) leukemia in a dog tha t we followed over a period of 2 years. Analysis of a hematological profile revealed lymphocytosis (19,500 lymphocytes per microliter; reference value s, 1,000-4,800 lymphocytes per microliter), with a majority of LGL on the b lood smear. LGL is defined as a lymphoid subset comprising 10% of periphera l blood mononuclear cells and corresponding to either CD3(-) CD8(-) NK cell s or CD3(+) CD8(+) T cells. The cells are characterized by abundant basophi lic cytoplasm containing distinct granules of variable size and number. The characteristic phenotype of our leukemic LGL is of a cytotoxic T cell, CD3 (+) and CD8(+). A new cell line, DLC 02, was established from the periphera l lymphocytes of the leukemic dog. Particles with type C retroviral morphol ogy were found in ultrathin sections of DLC 02 cell pellets. These particle s were found to have a sucrose gradient density of 1.17 g/liter and a rever se transcriptase activity with an Mn2+ preference, suggesting that they cor respond to a mammalian type C oncovirus.