Development of the nuclear inclusion bodies of infectious laryngotracheitis.

The formation of nuclear or cytoplasmic inclusion bodies is one of the more enigmatic phenomena which may result from virus infection. Some workers conceive the viral inclusion body as a "scar" arising from structural and biochemical alterations in the host cell (8). Others have suggested that some inclusion bodies perhaps result from cellular defense mechanisms (1). The results of diverse studies suggest that the nuclear inclusion body characteristic of herpesvirus infection is a "very active and complex biochemical nidus" (18) which is intrinsic in the production of infective material. Biochemical activity is indicated by changes in the structure and staining affinities of the inclusions during successive stages of their development. Some of the more outstanding changes in the developing inclusions are caused by variations in nucleic acid content. It has been demonstrated that, following infection of cells with herpes simplex virus, DNA is produced only in the central portion of the nucleus at the site of inclusion body formation (14) and that increasing DNA content of the cells results from the accumulation of viral rather than cellular DNA (23). Apparently, most of the DNA formed after infection is incorporated into developing virus particles within the nucleus. This supposition is based partly on the fact that the initial increase in virus titer of cultures coincides with the development of basophilic DNA-positive nuclear inclusion bodies (4,22,29). In late