A Transmissible Virus-Induced Lymphocytic Leukemia of the Cat<xref ref-type="fn" rid="FN2">2</xref>

Abstract

A spontaneous lymphocytic leukemia in a cat was transmitted to 56 of 68 inoculated kittens through 7 serial cell-free passages. The latent periods ranged from 30–139 days, with a median of 53 days. The induced lesions were, typically, a generalized lymphadenopathy with slight or moderate splenomegaly in some kittens. Histologically, the lesion was a malignant lymphoma of mixed histiocytic-lymphocytic cell type. A few experimental kittens developed a malignant lymphoma of more differentiated lymphocytic type. The experimental kittens had type C virus particles in, and budding into, intercellular spaces and, occasionally, cytoplasmic vesicles. The particles were approximately 110 mμ in diameter and morphologically similar to murine leukemia viruses. They occurred regularly in sections of bone marrow and less frequently in sections of plasma pellets, tissue cultures from neoplastic tissues, thymus, neoplastic lymph nodes, spleen, and liver. Electron microscopic examination of bone marrow biopsies was useful in monitoring experimental cats. The 107 negative biopsies on 50 cats and 34 positive biopsies on 18 cats were well correlated with other biological and pathological data. Tissue cultures derived from neoplastic lymph nodes or thymus or from bone marrow of the experimentally infected kittens produced large amounts of biologically active (leukemogenic) feline leukemia virus. Four experimental leukemic kittens that had received cell-free inocula also had liposarcomas. These solid tumors were multiple in 3 of the 4 cats. Type C virus particles budded from the surface of the liposarcoma cells.