Fine structure of epithelial cells of Lieberkühn's crypts in feline panleukopenia.

Electron microscopic observation was carried out on epithelial cells of Lieberkühn's crypts of cats naturally affected with feline panleukopenia. The most important change was the replication of feline panleukopenia. The most important change was the replication of feline panleukopenia virus in the nucleus with associated alterations in the lining epithelial cells of the crypts. In these cells in the early stage of infection, virus particles 20 nm in average diameter were found either singly or in small regularly arrayed clusters everywhere in the markedly swollen nucleus. In the course of infection, the nucleus of infected cells became rather atrophic with a marked margination of chromatin granules. Its major portion was occupied with masses of fine fibrillar substance. It was a "viral matrix area" in which appeared a large compact aggregate of virus particles showing a crystalline array. At the same time, the outer membrane of the nuclear envelope partially extended and disrupted. Membranous elements related to it in the cytoplasm were regularly distributed almost always with particles indistinguishable from the virus particles in the nucleus. From these results it was suggested that the major portion of the infected nucleus, or the site of viral replication, might correspond to the amphophilic intranuclear inclusion body revealed by light microscopy.