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Spontaneous nonthymic T cell lymphomas in young Wistar rats
S Hayashi1, T Nonoyama, H Miyajima
1Hikari Branch, Drug Safety Evaluation Laboratories, Takeda Chemical Industries, Ltd., Yamaguchi, Japan.
Abstract:
Spontaneous acute lymphomas and related leukemias, occurring in three of 2,974 male Wistar rats used as controls in toxicity studies during the last 14 years (1974-1987), were examined by light and electron microscopy and by using immunohistochemistry. At autopsy, conspicuous hepatosplenomegaly was noted. Morphologically, tumor cells of all three rats were medium-sized lymphocytes with many mitotic figures proliferating mainly in the spleen, liver, and bone marrow. Virus-like particles were not detected. Immunohistochemically, almost all tumor cells were positive for thy-1 antigen but negative for hematopoietic and differentiation markers such as W3/13, W3/25, OX4, OX8, and OX12. The results suggest that the lymphomas in these three rats were derived from T cells.