Studies on the nature of fibrillar nuclei. Distinction from viral nucleocapsid.

Despite sufficient evidence to the contrary, fibrillar nuclei continue to be claimed by some to represent paramyxovirus. In a review of the electron-microscopic material, fibrillar nuclei were found in a variety of tissues and situations where a viral etiology is unlikely. Fibrillar nuclei were most often found in postmortem and formalin-fixed material. These nuclei were also experimentally produced in postmortem human lung with formalin fixation followed by a deionized water rinse. It is concluded that fibrillar nuclei do not represent virus, but chromatin, and it is believed that this chromatin appearance is related to cell injury and to tissue processing. It is also believed that fibrillar nuclei occur with much greater frequency than realized. These nuclei are usually ignored during examination of specimens by light and electron microscopy because these specimens are usually being selectively screened for other changes and perhaps because a clear understanding of their significance is still lacking.