Paracrystal Formation in Cell Cultures Infected with Adenovirus Type 2

Abstract

Large rod-shaped structures corresponding to paracrystals were seen in the nucleus, cytoplasm, or both of adenovirus type 2 (Ad2)-infected cells by immunofluorescence staining with antibody prepared against purified Ad2. In exception to this, Ad2-induced crystals did not stain with either hexon or fiber antibody. The crystalline structures were first observed in Ad2-infected Vero cells at 28 hr with a maximum number at 70 hr postinoculation. The kinetics of paracrystalline formation closely paralleled the experimental synthesis of infectious progeny virus. Acridine-orange staining revealed the lack of nucleic acids associated with the crystal. Also, the paracrystals stained intensely with phenanthrenequinone, suggesting that they are composed of basic proteins. Interferon induced by Newcastle disease virus from African green monkey kidney cell cultures was used to pretreat Vero cells prior to Ad2 infection. This resulted in inhibiting the formation of viral-induced paracrystals in 97% of the cells and reduced virus yields by 95%. The African green monkey kidney cell culture interferon did not reduce Ad2 yields in HeLa cell cultures or display any virus inhibitory activity in rabbit kidney cell cultures. Staining procedures, fluorescent-antibody tests with whole virus, hexon or fiber antibody, and interferon studies suggested that the paracrystals were viral-directed and composed of basic proteins (possibly core proteins).

Inhibitory Effect of Abitylguanide on Adenovirus Replication

“…At first, there was no uniform opinion on what component of the viral proteins formed the paracrystals. Some researchers thought that they represented an accumulation of capsid proteins synthesized in surplus (superfluous capsid subunits) [40][41][42][43]; others specified that they were formed from the filiform (fiber) protein [44]; and a third group of researchers suggested that paracrystalpils of the basic core protein could appear in the nuclei or cytoplasm [45][46][47][48]. It was found that paracrystals appear after 24 h and do not grow larger, and the cell culture type does not influence their presence or size (V. Karabasheva and I. Dobrev, personal communication).…”

Bromodeoxyuridine Labelling to Determine Viral DNA Localization in Fluorescence and Electron Microscopy: The Case of Adenovirus

“…At late times (~24 hpi), virus particles and protein crystals formed by penton base and fiber start to appear [ 28 , 29 ] ( Figure 1 B). At 36 hpi, particle production reaches its maximum [ 30 ] ( Figure 1 G) and the cell morphology is extensively altered.…”