Basophilic intracytoplasmic viral matrix inclusions distributed widely in layer hens affected with avian-leukosis-virus-associated tumours.

Layer hens (310 days old) affected with subcutaneous tumours were investigated pathologically. Basopholic intracytoplasmic viral matrix inclusions (MIs) were widely distributed in the chickens affected with subcutaneous myxoma rhabdomyosarcoma, perineuroma, glioma, intra-abdominal adenocarcinoma, and nephroblastoma. MIs were observed in the myocardial cells and the impulse-conducting-system cells. They were also present in the smooth muscle cells of the arteries in the spleen and lungs, in the smooth muscle of the digestive tract muscular layer (crop, oesophagus, proventriculus, gizzard, duodenum, jejunum, ileum, caecum, and large intestine), and in the smooth muscle of the capsule in the ovary and pancreas. They were also observed in the podocytes of glomeruli and renal epithelium in the kidneys, tumour cells of nephroblastoma, chondrocytes of the trachea, squamous-epithelial cells of the pharynx, and nerve cells of the cerebrum and tumour cells of the glioma in the cerebellum. Histochemically, MIs were stained with RNA, but not with DNA. MIs in the various tissues were strongly positive for the avian leukosis virus (ALV) antigen. Ultrastracturally, MIs were found in the cytoplasm of myocardial cells and podocytes of renal glomeruli. They consisted of electron-dense small granules and ring-shaped particles. Viral particles were observed in the vesicles of the cytoplasm of myocardial cells and glomerular podocytes. The gene product specific for subgroup A of ALV was detected in the livers or tumours by reverse transcription-polymerase chain reaction. This result suggests that MIs can be formed in organs rather than muscular systems in the chickens naturally affected with ALV-associated tumours.