Neoplastic response of the avian liver to host infection with strain Mc29 leukosis verus.
Studies were made on the oncogenic response of 3086 young chicks to i.v. inoculation of MC29 avian leukosis virus from blood plasma of previous-passage birds or the supernatant fluid of cultures of chick embryo cells infected with strain MC29. Among the large variety of neoplasms of other tissues previously described, there occurred a high incidence of primary growths of the liver. Pathomorphology of the growths frequently differed greatly in both different hosts and the same bird, but some uniformity of the types of neoplasms was evident in many animals. Despite much variation in histopathology, the large proportion of growths could be grouped in several distinctive categories. Examinations by light and electron microscopy provided evidence of derivation of the tumors by alteration of hepatocytes originating principally in the portal regions as indicated by forms transitional from the parenchymal cells to the cells of the different types of growths. Neoplastic aspects of the growths were evident by infiltration and invasion of adjacent tissues, penetration of blood vessels, transplantability to other avian hosts (described in another report), and metastasis to distant organs including the lung, kidney, and spleen. There was no evidence of tumors arising from the biliary system, and growths of cells resembling the biliary type could be traced to altered hepatocytes. None of the findings suggested conversion of biliary-type cells to hepatocytes. Continued growth resulted in anaplastic and metaplastic changes in cell morphology and structural organization and in the formation of cartilage, osteoid, and sarcoma-like spindle-cell tumors of probable epithelial origin. Development of the growths wasnot associated with cirrhosis, and necrosis was limited to infrequent disseminated, essentially unicellular changes or necrobiosis of small groups of cells. The marked variations in the type of virus-induced growths demonstrated the remarkable capacity of cells morphologically inidistinguishable from the hepatocytes for the most diverse alterations in cell structure and tissue organization. This neoplastic response of hepatocytes to the MC29 strain constitutes the only demonstration thus far of the specific hepatocarcinogenic activity of an avian tumor virus.