Cytopathology of chick renal epithelial cells experimentally infected with avian infectious bronchitis virus

The renal ducto-tubular epithelial cells of chicks infected with the MA-87 strain of avian infectious bronchitis virus (IBV) were examined ultrastructurally. Infected epithelial cells containing IBV particles were more numerous in the collecting ducts, collecting tubules, distal convoluted tubules and Henle's loops than in the proximal convoluted tubules. Virus particles invaded host cells through endocytotic vesicles. Cytopathologic changes in the infected epithelial cells were manifested by a variety of organlle alterations including swelling of mitochondria, dilation of Golgi vesicles and an increase in the amount of rough endoplasmic reticulum (RER). Virus particles were produced by budding into RER and, rarely, toward the perinuclear space. As virus replication progressed, virus particles were enclosed mainly in the dilated RER, cytoplasmic vesicles or virus-containing electron-dense bodies. Virus particles were also found in vesicles of Golgi complex, the dilated perinuclear space, in some autophagic vacuoles or free in the cytoplasm. Virus particles were released by exocytosis through cytoplasmic vesicles, or appeared to be discharged through disrupted cell membranes. It was concluded that epithelial cells of lower nephron and ducts are the primary target cells in IBV-infected kidneys.