Lesions of bone and bone marrow in myeloid leukosis occurring naturally inadult broiler breeders

Lesions of bone and bone marrow in myeloid leukosis (ML) occurring naturall y in adult broiler breeders were investigated pathologically. During gross examination, nodules and protrusions were commonly observed on the surface of the sternum, ribs, vertebrae, and synsacrum. The bone marrow of all the bones of the body was pale in color. Histologically, granulated myelocytes proliferated in the bone marrow of various bones and in the periosteum of t he sternum, ribs, vertebrae, and synsacrum. The first proliferation of tumo r cells occurred in the bone marrow of epiphysis. The myelocytes invaded th rough haversian and Volkmann's canals from the bone marrow to periosteal ar eas. Hematopoiesis was suppressed by marked proliferation of tumor cells in the bone marrow of the whole bone. Atrophy was also seen in the bones, inc luding medullary bones of the chickens suffering from ML. Proliferation of myelocytes was seen in the bone marrow and periosteum of ossified cartilagi nous rings of the trachea and larynx. Marked proliferation of myelocytes wa s seen in the dura mater of spinal cords, and it subsequently depressed the spinal cords. Bone formation with cartilage was seen in the periosteum of the sternum having marked proliferation of myelocytes in the bone marrow an d periosteum. Ultrastructurally, tumor cells showed large nuclei and cytopl asm with large round electron-dense lysosomes. The virus particles were rar ely detected in the cytoplasm of tumor cells. The polymerase chain reaction test of tumor samples showed positive for subgroup J avian leukosis virus. This study indicates that the myelocytes can invade through the compact bo nes to the periosteum in the sternum, ribs, vertebrae, synsarcum, and ossif ied cartilage of trachea and larynx having thinner compact bones. In additi on, the periosteal osteogenesis with cartilage in the sternum may be reacti ve change against the bone atrophy because of the marked proliferation of m yelocytes.