Mesotheliomas of peritoneum, epicardium, and pericardium induced by strain MC29 avian leukosis virus.

Injection of strain MC29 avian leukosis virus into the peritoneal, pericardia!, and air sac cavities of the chicken resulted in high incidence of tumors of the mesothelium of the respective structures. As determined by light and electron microscopy, the growths arose as papillomas or expanding tumors by alteration of the squamous mesothe lium to spheroidal or cuboidal cells characterized by rounded nuclei with clear nucleoplasm and very large nucleoli and cytoplasm deeply stained with hematoxylin. With continued rapid growth, the nuclear features les sened somewhat, cytoplasmic staining diminished greatly, and the cell limits became indistinct. A second stage of metaplasia was marked by frequent alteration of the epithelioid cells to cartilage which increased both by con tinued alteration of peripheral mesothelioma cells and proliferation of chondrocytes. The tumors, sometimes isolated but usually coalesced in masses, were poorly en capsulated, contained little fibrous stroma, and showed no necrosis. They readily invaded contiguous visceral tis sues but did not metastasize to distant sites. Numerous virus particles were observed in the tumors together with occasional budding of the particles from the cell mem branes. The mesotheliomas were an addition to the al ready broad spectrum of responses to strain MC29 virus consisting of myelocytic growths, high incidence of renal tumors, primary tumors of the liver parenchyma, and singular aspects of morphological alteration of chick em bryo cells in vitro. These virus-induced tumors in the chicken closely resembled mesotheliomas of unknown etiology in man and bovines in both morphology and be havior.